Development of sustainable vegetable production systems for south Florida and Virginia based on use of cover crops and precision irrigation

Final Report for LS03-148

Project Type: Research and Education
Funds awarded in 2003: $179,776.00
Projected End Date: 12/31/2007
Matching Non-Federal Funds: $194,400.00
Region: Southern
State: Florida
Principal Investigator:
Waldemar Klassen
Tropical Research and Education Center
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Project Information

Abstract:

A biologically-based system for winter production of fresh-market tomatoes in south Florida was devised. In fields not heavily infested with nutsedges, root knot nematodes or Fusarium spp., this summer cover crop green manure-based system produced similar tomato yields but with higher profits than those in the methyl bromide-based system. The development of a biologically-based pepper production system is in progress. An organic potato production system based on legume and grass cover crops, developed in Virginia, produces more tonnage of tubers than the methyl bromide-based system. An inexpensive automated irrigation/fertigation system was developed with potential to facilitate vegetable production in proximity to fragile natural ecosystems.

Tables, figures or graphs mentioned in this report are on file in the Southern SARE office.
Contact Sue Blum at 770-229-3350 or
sueblum@southernsare.org for a hard copy.

Project Objectives:

1.Develop sustainable production systems for tomato, pepper and potato each based on use of nematode- and pathogen-resistant cover crops (cowpea, oat, sorghum sudangrass, sunn hemp, velvetbean) instead of chemical soil sterilants such as methyl bromide.

2.Assess the effects of a cover crop based system on (a) crop yields and (b) population densities of plant parasitic nematodes, weeds and other serious pests.

3.Conduct research to reliably attain major gains in crop yields (e.g. attempt to double tomato yields) through science-based management of irrigation, fertigation and improvement of soil quality. Study the feasibility of using automated irrigation system and soil moisture sensors to maintain the optimum moisture level in the root zone, and prevent leaching of nutrients.

4.Develop enterprise budgets of the cover crop-based production systems vs. those based on use of methyl bromide. Determine social or economic constraints to adoption of advantageous systems, and identify appropriate measures to facilitate adoption if warranted.

5.Disseminate research findings and facilitate adoption of sustainable vegetable production systems in Florida, Virginia and other southern states.

Introduction:

Currently the continuing production of certain important vegetable crops in the southeastern USA is facing three major challenges. These are (a) the phase-out of methyl bromide use in the U.S.A. (while methyl bromide use in Mexico will continue until 2015), (b) the competitive advantage under NAFTA of the Mexican vegetable industry, and (c) the need to intensively produce crops with minimal use of water, and without polluting ground and surface waters and the air .
From 1990 to1998, the share of the U.S. vegetable market met by U.S. growers fell from 80 to 70 %, and that of Florida growers from 35 to 25 %. For tomato (Lycopersicon esculentum Mill.) the loss of market share has been even greater. In 1992, U.S. producers and Florida producers supplied 90 and 47 % of the U. S. tomato market, respectively, but by 1998 the corresponding figures were 67% and 25%. Upon the total ban of methyl bromide, tomato yields are expected to decline further by 10 % throughout Florida and by 20 % in Miami Dade County, where use of Telone, a substitute for methyl bromide, is not approved because it would leach into drinking water (VanSickle et al., 2000).
Thus, tomato production in Miami Dade and Palm Beach Counties is projected to cease completely. Florida is projected to lose $69 million annually in shipping point revenues for tomatoes, and Mexico to gain $52 million. Florida will also lose 65 % of the pepper market, mostly to Mexico, while production is expected to cease entirely in Miami Dade County and decline by 79 % in Palm Beach County. Clearly vegetable production in southern Florida depends upon the development of new production systems that do not need methyl bromide, and that substantially reduce the unit cost of production.
The search for potential solutions to the imminent void that will be created by the total ban of methyl bromide has taken several directions including chemical, biological, and cultural as well as combinations of two or more alternatives. Just to mention a few, the chemical alternatives include the use of soil fumigants such as Telone C-17 (Eger, 2000; Gilreath et al., 1995), metam sodium (McMillan et al. 1998a; Pinkerton et al., 1996), and methyl iodide (McMillan et al. 1998b). Cultural alternatives include heat treatments such as soil solarization (Chellemi et al., 1997; 1999; Stapleton and Devay, 1995), hot water treatment (Noling, 2000), and a combination of soil solarization and fumigation (Gilreath et al., 2000). Biocontrol of root-knot nematode by single-spore isolates of Pasteuria penetrans has been proposed (Kaplan et al., 1995). Likewise, Acremonium butyric, Chaetomium globosum, Gliocladium roseum, Trichoderma hamatum, and Zygorrhynchus moelleri fungi have been reported to reduce the populations of Fusarium, Penicillium, and Mucor when applied to compost in a soilless culture planted into tomatoes (Sivapalan et al., 1994). Finally, microbial pathogens that have been reported to be effective against nematodes include the bacteria Pasteuria penetrans and Bacillus thuringiensis (DuFour et al., 1998).
The development of vegetable cultivars with resistance to soil-borne pathogens and plant parasitic nematodes has been steadily progressing (Scott 1998), and disease and nematode resistant cultivars are likely to be key technologies in vegetable production systems that do not involve soil fumigation. In 1968 ‘Walter’ a cultivar resistant to Fusarium oxysporum f. sp. lycopersici race 2, and in 1976 ‘Flora-Dade’, a cultivar resistant to both Verticillium wilt and Fusarium wilt races 1 and 2 were released from the Tropical Research and Education Center, Homestead, FL (Scott, 1978). More recent releases include ‘Agri 6153’ resistant to Verticillium wilt race 1 and to Fusarium wilt, races 1 and 2 and to Stemphyllium gray leaf spot (Scott, 2004), ‘Solar Fire’ resistant to Fusarium races 1, 2 and 3 and to Verticillium wilt race 1 (Scott, 2003), and ‘Sebring’ resistant to Fusarium races 1, 2 and 3 and to Verticillium wilt race 1 (www.rogersadvantage.com).
Introducing genetic resistance to root knot nematodes into cultivars of vegetables has been successful in ‘Sanibel’, ‘Sun jay’, ‘Clemente’, ‘Cisco’, ‘Shady Lady’, and other tomato cultivars and in ‘Charleston Bell’, ‘Carolina Wonder’ and other pepper cultivars (DuFour et al., 1998). Likewise, several cultivars of leguminous and grassy cover crops have been identified as non-hosts or resistant to root knot nematodes (McSorley, 2000; McSorley et al., 1994; Peet, 1996; Yepsen, 1984). Some of these nematode-resistant host plants thrive well in tropical climates and include sunn hemp (Crotalaria juncea) and Dolichus lablab (Araya and Caswell-Chen, 1997), velvetbean (Mucuna deeringiana) (Kloepper et al., 1991; Rodriguez-Kabana et al., 1992a, 1992b; Vargas-Ayala and Rodriguez-Kabana, 2001; Vincente and Acosta, 1987; Weaver et al., 1998), castor bean (Ricinus communis), cowpea (Vigna unguiculata), cv. Iron Clay and American jointvetch (Aeschynomene americana) (McSorley, 1999). Nematode resistant grasses include oat (Avena sativa), sorghum (Sorghum bicolor) and bahia grass (Paspalum notatum) (Rodriguez-Kabana et al., 1989)
On the alkaline limestone-derived soils in Miami-Dade County, yellow nutsedge, Cyperus esculentus, is a potentially devastating weed pest in plastic mulch covered tomato and pepper beds, but purple nutsedge, C. rotundus, is of lesser importance. These two species readily penetrate the plastic mulch. However our experience has shown that moderate densities of these shade-intolerant nutsedge species can be sufficiently weakened by dense plantings of a cover crop so that subsequently applied plastic mulch is quite effective in suppressing such nutsedge populations. Also spiny pigweed, purslane, parthenium, ragweed, nightshade and various grasses, which are annually recurring problems, can be controlled by a dense cover crop stand followed by application of plastic mulch on the raised bed. On the other hand all of these weed species must be controlled in the aisles between beds by application of S-metolachlor and metrabuzin or other herbicides.
There are significant differences in species of plant-parasitic nematodes typically found in Florida’s sandy soils and those found in the calcareous soils in the southeastern Florida (McSorley et al 1985). Sandy soils are often inhabited by the sting nematode, Belonolaimus longicaudatus Rau, the awl nematode, Dolichodorus heterocephalus Cobb, and stubby-root nematodes Paratrichodorus spp., which can affect tomato and pepper, but these species are not prevalent in southeastern Florida soils. However the root-knot nematode is among the most common and the species Meloidogyne incognita (Kofoid & White) Chitwood) is an important pest of all major vegetable crops and causes economic losses on both soil types.
It has been proposed that a combination of crop rotation and genetic resistance is currently the only major management tool available that is effective and economical in fields where mixed populations of Meloidogyne spp. and H. glycines occur (Rodriguez-Kabana et al., 1990, 1998; Weaver et al., 1993). In view of this proposal, we hypothesized that in soils that are lightly to moderately infested with root knot nematodes, the use of nematode-resistant cultivars of tomatoes and cover crops will allow production of an economic crop without soil fumigation provided that the fields are kept free of weeds that serve as hosts to nematodes. We set forth to test this hypothesis by growing field tomatoes in south Florida during the falls/winters of 2001, 2002, and 2003.
Currently in Virginia, approximately 6,000 acres of Irish potato are planted annually with a cash value of over $8 million. Potato acreage has declined by 65% from 17,000 acres produced in 1984. Reduced production has occurred in part because of low marketable tuber yields, resulting from incidence of pests including weeds, Colorado potato beetle and nematodes. Normally, edaphic and above-ground temperatures are more severe for potato growth and development in the southern states than northern states. To be both competitive and sustainable, Virginia and other southern states need organic-based production systems that moderate the growing environment and improve soil productivity.
Cereal grains such as rye (Secale cereale L.), either grown alone or mixed with legume crop in rotation with vegetable crops, are known to greatly reduce losses caused by weeds (Bellinder and Wallace, 1991; Morse, 1999), Colorado potato beetle (Wyman et al., 1994), and nematodes (Belair and Parent, 1996; McSorley, 1998). During the past eight years at Virginia Tech, high ¬residue no-tillage (NT) systems have been developed for production of potato. Tuber yield with NT has been equal or higher than with conventional tillage. In these NT systems, high-residue (6-12 metric tons dry mater/ha) cover crops were grown on preformed (established in the fall before seeding cover crops) raised beds to provide controlled traffic lanes and thick in-situ organic mulch layer that favor weed suppression and reduced applications of growth inputs
(water, nutrients and pesticides) (Morse, 1997).
Automation of irrigation systems and the use of soil water sensing devices such as tensiometers have been investigated by many researchers. Automation in this context generally consists of a sensor (soil water content, soil tension, water level, etc.), a control system, and irrigation system components. The use of soil water based feedback to control irrigation has been documented as saving water while maintaining crop yields. Phene and Howell (1984) used a custom-made soil matric potential sensor to control subsurface drip irrigated processing tomatoes. Their results indicated that yields of the automated system were similar to those from tomatoes irrigated with a system based on pan evaporation with the potential to use less irrigation water.
Coarse (sandy, gravelly) soils like those of Florida and many other regions of the world present special challenges when using soil water sensors. Switching tensiometers have been used on commodities such as fresh market tomatoes (Smajstrla and Locascio, 1996) and citrus (Smajstrla and Koo, 1986) to automatically control irrigation events based on preset soil matric potential limits. Smajstrla and Locascio (1996) reported that using switching tensiometers placed at 0.15 m depths and set at 10 and 15 kPa tensions in a North Florida sandy soil reduced irrigation requirements of tomatoes by 40-50% without reducing yields compared to common irrigation scheduling practices in the area where water is applied on a fixed schedule (3-5 times per/week). Munoz-Carpena et al. (2005a) found that a switching tensiometer-controlled drip irrigation system set at 15 kPa on tomatoes reduced irrigation 70% compared to typical farmer practices in a south Florida sandy soil while maintaining similar yields. In spite of these results, tensiometers have not been widely adopted for vegetable production in coarse soils due to the very frequent maintenance required (Munoz-Carpena et al., 2003). This frequent maintenance is due to discharge caused by limited contact with the coarse sandy soil, organic growth on the ceramic cups, and the need for re-calibration that makes Tensiometers impractical for automated irrigation control when used in these soils (Smajstrla and Koo, 1986; Munoz-Carpena, 2005a).

Granular Matrix Sensors (GMS) and dielectric sensors like Time Domain Reflectometry (TOR), capacitance, etc., require less field maintenance than tensiometers (Munoz-Carpena et al., 2005b) and thus have a greater potential for commercial adoption. However, Munoz-Carpena et al. (2005a) observed that a GMS controlled drip irrigation system in sandy soils of South Florida failed to bypass most irrigation events that were intended to be overridden due to slow response time. Irmak and Haman (2001) found similar results for GMS in sandy soils of North Florida and concluded that these sensors are not sufficiently responsive to changes in soil tension to control irrigation. Recent low cost dielectric probes are now available that could be a reliable and low maintenance alternative to automatically control irrigation.

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Wyman, J. A., J. Feldman and S. K. King. 1994. Cultural control of Colorado potato beetle: Off-crop management. p. 376-385. In: G. N. Zehnder, M. L. Powelson, R. K. Jansson, and K.V. Raman (Eds.). Advances in Potato Pest Biology and Management. APS Press, St. Paul, Minnesota.
Yepsen, R. B., Jr. (ed.). 1984. The Encyclopedia of Natural Insect and Disease Control. Rev. ed. Rodale Press, Emmaus, PA. p. 267-271.

Cooperators

Click linked name(s) to expand
  • Yuncong Li
  • Ron Morse
  • Rafael Munoz-Carpena
  • Teresa Olczyk
  • Qingren Wang

Research

Materials and methods:

Florida Component:
No.1. Biologically-based tomato production system*.
*Note: This experiment was initiated in 2001 without the benefit of support from SARE Project# LS03-148. When the latter grant was approved, this project was continued and expanded.

Field experiments were conducted for three years at Homestead, Florida. In the first two years, the experiments were conducted at the Tropical Research and Education Center (TREC), University of Florida, Homestead, and in the third year at Pine Island Farms (PIF), a commercial vegetable production farm about 22 miles northeast of TREC. The soil at TREC is Krome, very gravelly loam (loamy-skeletal, carbonatic hyperthermic lithic Udorthents) and consists of about 33% soil and 67% pebbles (>2mm). The soil at PIF is Opalocka (sandy, siliceous, hyperthermic lithic Udorthents). The experiment in year 1 consisted of three treatments: two cover crop treatments, ‘Iron Clay’ cowpea and velvetbean (cultivar not specified), and one methyl bromide/ chloropicrin (MC-33) treatment at 392 kg ha-1 which contained 330g kg-1 chloropicrin (Helena Chemical Co., Florida City, F La.). In year 2, ‘Tropic Sun’ sunn hemp was added to the year 1 treatments as a third cover crop treatment. Each year the fields were disked three times and raised beds 15-cm high were formed. The experiments were laid out in a randomized complete block design. Each treatment was applied to three raised beds each 13.5-m long by 1.8-m wide (center-to-center). A distance of 5m separated the various treatments. Plots 6-m long were randomly designated from the middle row for yield determination. There were four replications per treatment in each year. In order to suppress weeds in the aisles between the raised beds S-metolachlor and metrabuzin were incorporated into the soil after the beds had been formed. If needed one or more additional in-season applications of metrabuzin were made. Fallow plots were maintained weed-free by rototilling.
In year 3, the experiment at PIF consisted of four treatments—sunn hemp, velvetbean, an MC-33 soil fumigation treatment following a summer sorghum sudangrass cover crop, and a fallow treatment which was kept weed free. The field was disked as in the previous two years and the raised beds were formed as described earlier. The experiment was laid out in a randomized complete block design with four replications for each treatment. Each treatment consisted of a double-bed 26-m long with plants spaced 0.6 m within the row. Because of some differences in management practices and dates of various operations from year to year, some imposed by the grower, each year will be described separately to point out these differences.

Year1. Rhizobium-treated seeds of the leguminous cover crops and sorghum sudangrass were seeded in mid-June using a Tye no-till drill (AGCO Corp., Lawrenceville, GA). Seeding rates for cowpea and velvetbean were 112 kg ha-1 and 34 kg ha-1, respectively. The cover crops received no fertilizer during the growing season. They were flail-mowed on 16 Aug. Above-ground samples of biomass were taken and biomass yield was determined. The beds were reseeded and biomass samples were taken again for biomass determination before the crops were flail-mowed on 12 Oct. The cover crop residues were incorporated into the soil using a spader (Imants Heavy Duty, Imants USA/ Autrusa Co., Perkeomenville, PA) during the second week of Oct. During the first week of Dec., dry fertilizer (6N-2.6P-10K) was applied at the rate of 1123 kg ha-1 for the MC-33 treatment and 392 kg ha-1 for the two cover crop treatments. The fertilizer was banded 25cm each side of the bed center and roto-tilled into the soil for all treatments. The beds were then reformed. Immediately thereafter, MC-33 was injected into the appropriate beds at 392 kg ha-1 of MeBr, and two drip lines and white-on-black plastic mulch were laid on all beds. Nematode-tolerant ‘Sanibel’ tomato seedlings were transplanted into the beds on 19 Dec. Beginning 15 Jan., an additional 180 kg ha-1 of N was applied as liquid 4N-0P-6.6K to all treatments through the drip lines twice a week starting at a rate of 1 kg N ha-1 day-1, and beginning 8 Feb., it was increased to 3.6 kg N ha-1 day-1 up to the first harvest. The rate was thereafter reduced to 1 kg N ha-1 day-1 up to one week before the final harvest. This made a total of 247 and 214 kg N ha-1 for the MC-33 and the cover crop treatments, respectively. Due to low price during that season, only two tomato harvests were made, one harvest on 30 March and the other on 13 April.

Year 2. As in year 1, the experiment was laid out in a randomized complete block design with four replications. Rhizobium-treated seeds of cowpea, velvetbean and sunn hemp were seeded on 9 May. Seeding rates for cowpea and velvetbean were as in the previous year and for sunn hemp, it was 56 kg ha-1. On 13 July, the cowpea was flail-mowed at ground level and the sunn hemp was flail-mowed at 75 cm above ground level to induce profuse branching (Abdul-Baki et al., 2001). Residues from the first mowing were left to decompose in the field. The cowpea plots were reseeded on 18 July. Subsequently, on 1 Oct., all three cover crops were flail-mowed and incorporated into the soil. As in the previous year, biomass samples were taken from each treatment before mowing, dried, and total biomass determined. In mid-October the raised beds were reformed and 1235 kg ha-1 of 6 N-2.6 P-10 K fertilizer was applied and roto-tilled into the soil of all treatments. Two drip lines were installed into each bed, MC-33 was applied to the appropriate treatment as before and the beds were immediately covered with polyethylene mulch. Five-week-old seedlings of ‘Leila’, a nematode-susceptible cv. were transplanted into the beds on 9 Nov. As in year 1, an additional 180 kg ha-1 was applied as liquid 4N-0 P-6.6 K to all treatments through the drip line thus resulting in a total application of 247 kg N ha-1 for all treatments following the application regime of year 1. Three harvests were made: 6 Feb., 5 March, and 25 March.

Year 3: The experiment in the third year was conducted at Pine Island Farms (PIF), a commercial production farm described by the grower to have moderate-to-high nematode population densities. Two cover crop treatments were velvetbean and sunn hemp. Two additional treatments were fallow (no cover crop or soil fumigation), and summer sorghum sudangrass followed by MC-33. This last treatment is commonly used by large-scale conventional growers in south Florida. The cover crops (including sorghum sudangrass, which was part of the MC-33 treatment) were seeded on 9 June and an irrigation system was installed to deliver water as needed. Seeding rate for sorghum sudangrass was 45 kg ha-1 and for the other cover crops, as in previous years.
The fallow plots were kept weed free. On 22 Aug. the cover crops were prematurely plowed under before the biomass samples could be taken. Fertilizer was applied to all treatments as N6-P6-K12 at an N rate of 247 kg ha-1 and incorporated into the soil. The beds were reformed and MC-33 was injected into the appropriate beds as in previous years. Two drip lines and white-on-black plastic mulch were laid on all beds. On 11 Nov., five-week-old seedlings of nematode-resistant ‘6153 Rogers’ (Rogers Seed Co., Greensboro, NC) were transplanted. Additional liquid fertilizer (N13-P0-K46) was applied twice-a-week for five weeks starting at fruit set at a rate of 8 kg per application thus bringing the N application to a total of 300 kg ha-1. All other cultural practices were the same as in the previous two years.
Eight on-vine-ripe fruit harvests were made at the breaker to pink stages between 17 Feb. and 31 March. The last harvest included unripe marketable fruits. The fruits were graded in accordance with Florida Tomato Committee standards (Brown, 2000) and separated into extra-large, large, and medium. Market prices during that year were favorable even for medium-size fruits. All cultural operations were done by the grower in the same manner he managed the rest of his large-scale tomato field. Pesticides were applied according to standard growers’ practices (Maynard and Olson, 2000).

Nematode and root health evaluation. Root-knot nematode gall ratings were evaluated on 250 cm3 soil samples taken at three time intervals during the production season: before seeding the cover crops; before transplanting the tomatoes; and at the end of tomato harvest. Likewise, tomato root health was determined at the end of harvest by examining necrosis caused by root rot (primarily Rhizoctonia solani), and gall formation by the root knot nematode. In each case a 0 to 5 scale was used as proposed by Taylor and Sasser (1978) for nematode density and by Coyler (1988) for root rot.

Statistical Analysis. Data were analyzed statistically using analysis of variance (ANOVA) and Duncan’s multiple range test using SAS (Version 8.1, SAS Inst. Inc., Cary, NC, USA).

No. 2. Use of summer cover crops and organic mulch to improve tomato yields and soil fertility.
Site description
The experiment was conducted at the Tropical Research and Education Center, University of Florida, Homestead, Florida. At this site the average annual rainfall is 1,499 mm of which an average 76% falls between June and October, the annual temperature averages 23.9 oC and usually ranges from a maximum of 35 oC in June to a minimum of 5 oC in January (Wang et al., 2002a). The soil is a Krome very gravelly loam (loamy-skeletal, carbonatic, hyperthermic Lithic Udorthents), which consist of 58.8% gravel (> 2 mm), and a gravel-free fraction. The latter consists of 48.4% sand, 30.3% silt, and 21.3% clay. CaCO3 comprises about 60% of the soil, organic C is 11.3 to 18.0 g kg-1, total N is 0.9 to 1.3 g kg-1, the soil pH is 7.6 to 7.8 (water), ABDTPA (ammonium bicarbonate-diethylene triaminepentaacetic acid) extractable phosphorus (P) and potassium (K) are 16.5 to 26.8 mg kg-1 and 123.5 to 132.6 mg kg-1, respectively.

Experimental design and management
The field experiment was conducted in three consecutive years from 2002 through 2005 using a randomized split-plot design. The main plots consisted of four cover crops, sunn hemp, velvetbean, cowpea and sorghum sudangrass, grown from June to September, and fallow as a control, and all plots were on raised beds. In the first year compost was applied as an organic mulch (OM) to some plots at the single rate of 50 t ha-1 dry weight, while white on black plastic mulch (PM) was installed on others. In the second and third years, the 50 t ha-1 treatment was applied to the very same plots as in the first year of the experiment, and three additional compost treatments were made, i.e., 25 t ha-1, 50 t ha-1, and 75 t ha-1. Thus the four organic mulch treatments are denoted as OM1-25, OM1-50, OM1-75, and OM2-50 in the second year and as OM2-25, OM2-50, OM2-75, and OM3-50 in the third year, respectively.
The seeding rates of cover crops were 56 kg ha-1 for sunn hemp, 112 kg ha-1 for cowpea, 45 kg ha-1 for both velvetbean and sorghum sudangrass. In order to promote branching and increase the production of high quality biomass, the apical dominance of the sunn hemp was overcome by cutting the stems at 30 cm above the ground in the middle of August (Abdul-Baki et al. 2001.). The cover crops were terminated by flail-mowing, incorporated into the soil in mid September each year. Early in October, 1120 kg ha-1 of dry fertilizer (6 N-6 P2O5-12 K2O) was rototilled into the soil together with the cover crop residues. Then the raised beds 15-cm high, 91-cm wide and 182-cm between centers of two adjacent beds were re-formed. Compost was supplied to the appropriate plots by means of tractor-powered calibrated spreader. Each plot consisted of a 15-m long section of a raised bed, which was 27 m2. Two parallel T-tapes, each 18 cm from the center of the bed were installed and connected to a layflat hose, which provided the water for drip irrigation. Tomato (Lycopersicon esculentum (Mill.)) ‘Sanibel’ in 2002, and ‘Florida 47’ in 2003 and 2004, respectively. Seedlings were transplanted into in a single row on each bed with 50-cm between plants. Practices to control foliar insects and diseases were applied according to Maynard and Olson (2000). Each year starting from the sixth week after tomato transplanting, 328 l ha -1 of liquid fertilizer consisting of 4 N-0 P2O5-8 K2O was delivered through the drip lines once per week until the second harvest.

Harvests and grading
Tomato fruits were harvested three times each year. The first harvest was conducted when about 10% of fruits had turned red, and only red or pink, and extra large green and large green fruits (“mature green” fruits) were harvested during this time. Two or three weeks later, the second harvest was similarly performed. Finally 3 or 4 weeks after the second harvest, the third harvest was conducted, which included all fruits equal or larger than the small size. Harvested fruits were separated by machine (Kerian speed sizer, Kerian Machine, Inc., Grafton, ND) according to the Florida Tomato Committee Standards (Brown, 2000) into extra-large, large, and medium and small sizes. Defective fruits were culled manually. The fruits in each size category as well as the culls were weighed. Extra-large, large, and medium fruits constituted the marketable yield, and the small and culled fruits constituted the non-marketable yield.

Sampling and analysis
Soil samples (0-10 cm in depth) were collected before the cover crops were seeded, after the cover crops had been soil-incorporated but before tomato seedlings were transplanted and at tomato flowering. Above ground biomass samples of the cover crops were collected each year before they were terminated by flail-mowing. At the flowering, the height and canopy diameter of each of 5 randomly selected tomato plants from each plot were measured and the canopy area was calculated. The chlorophyll content of the third fully expanded leaf from the top of each of these same tomato plants was determined with a SPAD-502 meter, and then this leaf was collected for further analysis.
Soil samples were air dried and ground to pass through a < 2 mm mesh sieve. Plant biomass samples were oven dried at 70 oC for >72 hr before being ground to pass through a <1 mm mesh sieve for chemical analysis. Total N of soil and plant samples was determined with a CNS auto-analyzer (Vario Max Elementar, Hanau, Germany). Soil organic carbon was determined by the weight loss-on-ignition (WLOI) method (Schulte and Hopkins, 1996; Jolivet et al., 1998). In order to determine the total nutrient elements other than N, the samples were digested with concentrated nitric acid-hydrogen peroxide-hydrochloric acid (HNO3-H2O2-HCl) according to the USEPA method, 3050A (USEPA, 1990), then analyzed via inductively coupled plasma optical emission spectroscopy [ICP-OES (Ultima 2C) Horiba Jobin Yvon Inc., Edision, N.J.]. Soil sub-samples were extracted with AB-DTPA for colorimetric determination of extractable P, and for ICP-OES determination of extractable K. The composition and properties of compost used in the experiment were determined with the methods used for the soil samples, and the data were summarized in Table 1. At the end of the third year, soil physical properties, e.g., soil bulk density (Blake and Hartge, 1986), field capacity and hydraulic conductivity (Jury and Horton, 2004), etc. were determined. Statistics
By means of the SAS program (SAS Institute, version 8.1, Cary, N.C.), the data were subjected to ANOVA and the means were separated using Duncan’s multiple range test.

No. 3. Automated irrigation/fertigation system.
Development of the soil water controller
A quantified irrigation control (QIC) system was developed around a custom-built integrated circuit (IC) board and a commercially available capacitance based soil water probe (0.20 m ECH20 probe, Decagon Devices, Inc., Pullman, WA). Most materials are readily available electronic components except for the custom-built IC board. The soil water probe used in this research could be replaced with any type of sensor that has a predictable voltage response to variation in soil water or tension. The total cost of the controller components without the sensor, not including shipping of components or labor for assembly was US$64 (US$124 with the sensor). This compares favorably with existing commercial alternatives including switching tensiometers and other dielectric probe based controllers.
The programmable microcontroller used in this system (MSP430-FETI49, Texas Instruments Inc., Dallas, Texas) contained a 16 bit timer with a 12 bit analog to digital (A/D) converter and was developed for ultra low power applications (0.1-250 A). The 12 bit A/D converter allows the 250 (dry) – 1000 (wet) mY signal sent from the probe to be resolved to 0.18 mY, which translates into <0.01 % volumetric soil water in South Florida soils.
The QIC microcontroller queries the probe at user set intervals by sending a 25 millisecond 2.5 YDC excitation signal to the capacitance probe. Normally, this comparison occurs every minute (adjustable via a software interface with the microcontroller). If the voltage returned from the probe is below a user set threshold (potentiometer), then the controller allows the time clock 24 YAC signal to power the irrigation solenoid valve via the on board latching relay. When the signal is higher than the set point the relay opens to stop irrigation. Since several 1 minute sampling cycles are possible within an irrigation event, it is possible for the system to irrigate for periods shorter that the duration of the scheduled event, i.e. there is no minimum irrigation time per se, other than the querying and sensor response lag time.
The QIC can be powered by either a 9V DC battery or by the power from the controller (24 V AC when the time clock sends a signal), both of which are transformed to 5V DC. The advantage of using a battery is that the voltage of the soil water probe can be checked while in the field without need for the controller to power the irrigation zone containing the QIC in question. The QIC can also be used in the place of a time based irrigation controller for a single irrigation valve and a 24V AC power supply. Although this configuration was not used in the experiment, it would allow for complete irrigation control based on soil water conditions. By connecting the on-board jumper the QIC will query the probe every four seconds to determine the probe output directly from the IC board.
The potentiometer can be adjusted until the LED activates, which establishes the QIC set point. This provides the alternative to select the set point in the field when the soil water level is at optimal conditions such as field capacity without the need for a specific soil calibration.

Site selection and probe calibration
The first experiment was conducted at the Tropical Research and Education Center in Homestead, FL on a Krome gravelly-loam “rock-plowed” soil (loamy-skeletal, carbonatic, hyperthermic Lithic Udorthents) of 0.30 m average depth (with a range of 0.10-0.40 m) overlaying porous limestone bed rock, (USDA, 1996). The physical properties at the site are summarized in Munoz-Carpena et al., (2002).
Although the manufacturer of the soil water probe used here provides a general linear calibration equation (Decagon Devices, 2002), a specific calibration was developed for soil from our test field. The soil was sampled at three different field locations from a depth of 0 to 0.21 m with care to obtain the gravel and fine portions as present in the field. After collection, each sample was homogenized independently by tumbling in a bucket with a lid for 15 seconds, and then hand-packed in 3 PYC cylinders (0.10 x LO.21 m) bounded at the bottom with a stainless steel fine wire mesh held by a metal bracket around the tube. To achieve the original field bulk density the packing was done in four layers of equal thickness. A capacitance probe was inserted vertically in the center of each core and the samples saturated from the bottom up during 24 hr using a solution of 0.005 M CaS04 saturated with thymol (Klute and Dirksen, 1986). Once saturated the probe outputs (mY) were read with a handheld reader (ECH2O Check, Decagon Devices, Inc., Pullman, WA) and the cores weighted on a laboratory scale of 0.000 I kg of resolution over the 0-8.0 kg range. The cores were then placed on a wire screen to allow free drainage and air-drying while frequent probe readings (mY) and weights (kg) were recorded. When the volumetric soil water reached 17%, value below those typical of irrigated field conditions, the probe was removed and the soil dried in a laboratory oven to obtain the dry weight needed to calculate the volumetric water content for each reading. A total of 25 paired probe readings and volumetric water content data collected from the three cores were fitted to a straight line. Thus, an average calibration over the entire field was applied to all probes use for irrigation control rather than a specific calibration of each probe location.

Field testing of the controller
A field at the University of Florida’s Tropical Research and Education Center in Homestead, FL in which sorghum sudangrass had been grown as a summer cover crop was utilized for this experiment. Tomatoes were cultured according to local horticultural practices. A fumigant (66:33 volumetric mix of methyl-bromide:chloropicrin, MC-33) was injected into the soil at 392 kg/ha during the formation of the raised beds, and immediately thereafter the drip lines and plastic mulch were installed. Pre-plant dry fertilizer (6-6-12) at 1867 kg/ ha was roto-tilled into the bed. The tomato seedlings (cultivar ‘FL 47’) were transplanted on November 20, 2003 into plastic mulched raised beds spaced 1.8 m apart in one row per bed with plants spaced 0.46 m apart. Each plot was 16.7 m long. Irrigation was supplied with dual drip irrigation lines (T-TAPE TSX 508-12-450, T-Systems International, Inc., San Diego, CA with 0.015 m internal diameter, 0.30 m emitter spacing, 1.0 Uh emitter discharge at 69 kPa, and 0.002 m thickness) under the plastic mulch and approximately 0.30 m apart on either side of the tomato row. Dissolved fertilizer (4-0-8) at 19.6 kg N/ha was applied manually to each individual plant only during each of the final five weeks prior to harvest. Tomatoes were harvested four times during the period March 1-18, 2004 from a 6.1 m section within each plot. Harvested fruits were graded following Florida Tomato Committee standards (Brown, 2000). Irrigation treatments were implemented at 20 days after planting to allow the transplants time to become established. Prior to that date, all experimental treatments were irrigated at least once each day on the same schedule. Thereafter irrigation treatments were established in a completely randomized design with four replications. Irrigation scheduling mechanisms consisted of switching-tensiometer, historical weather, and practices used by local growers.. The tensiometer, QIC, and weather-based methods were set to irrigate a maximum of five times each day for one hour total. The grower-based treatment was irrigated once each day for one hour similar to practices in the region. Tensiometer and QIC methods allowed irrigation only if soil tension exceeded set points for tensiometer treatments, or if soil water was below set points for QIC treatments, respectively. The tensiometer treatments consisted of switching tensiometers (low tension model TGA-LT, Irrometer Co., Riverside, CA) set at 10 kPa and 25 kPa for the two treatments, respectively. The QIC treatments were set at two thresholds of 425 mY (95% confidence interval of 420-430 mY) and 450 mY (95% confidence interval of 445-455 mY), corresponding to the soil water status at 25 kPa and 10 kPa obtained using the soil water release curve given by Al-Yahyai et al., (2006) for the gravelly-loam soil of this site. This voltage threshold was used previously for the gravelly-loam soil (Munoz-Carpena et al., 2005a) and verified at the beginning of the experiment. Weather-based treatments were irrigated according to calculated crop evapotranspiration (ETc) that was calculated by the local historical daily average reference ET (ETo) multiplied by the published crop coefficient (Ke). For our crop and area the Kc values used were: 0.3 (from 11/20-12/3), 0.6 (12/4-12/23), 1.15 (12/24-2/12) and 1.00 (2/13-3/18) (Simonne et al., 2004). Historical average seasonal ETc in this area is 291 mm (Simonne et al., 2004). The historical weather-based treatment was irrigated according to the average long-term maximum daily ETo throughout the season. The grower practice irrigation treatment consisted of one hour of irrigation per day throughout the season (3.7 mm/d).
Water use in each plot was continuously and independently recorded by a positive displacement
water meter equipped with a magnetically actuated reed switch (PSM- T 0.016 X 0.013 m (5/8″ X
1/2″), ABB Water Meters, Inc., Ocala, FL) connected to an event data logger (H7-002-04, Onset
Computer Corporation, Bourne, MA). Weekly readings were also manually taken from the counters in each water meter. The water meters were installed at the inlet of each plot upstream of the pressure regulator and a solenoid valve.
For each treatment irrigation water use efficiency (IWUE, kg/m2) was calculated by dividing the sum of the marketable yield by the total amount of water applied during the season. One-way analysis of variance and comparison of means using Tukey Kramer HSD were performed on irrigation water, yield and IWUE (JMP 6, SAS Institute, Cary, NC, 2005). This test controls the type 1 errors of all comparisons simultaneously, rather than a pair of means at a time.
Weather parameters such as temperature, relative humidity, incoming solar radiation, wind speed, and precipitation were measured on-site by the Florida Automated Weather Network (FAWN) system. Daily ET was calculated by the modified Penman method as described in Jones et al., (1984).

Field installation and operation of the controller
Switching tensiometers and ECH2O probes were installed vertically 3 m away from the solenoid valves in the center of the bed, between the paired irrigation lines and two consecutive tomato plants of each experimental plot. The ECH2O dielectric probes were inserted in the top 0.20 m, roughly equivalent to the total bed depth, whereas the porous cup of the switching
tensiometers was placed at the midpoint of the bed depth, i.e. 0.10111. Thus an average soil water status was obtained for entire bedded soil profile of the tomato plants with both types of probes. The QIC was placed nearby on top of the vegetable bed. Although the QIC was designed within a waterproof metal housing, the entire apparatus was placed within a plastic food storage container. Both the QIC and plastic container contained a desiccant to prevent
condensation on the inside of the containers. For the first week of QIC operation, readings were
collected from manual tensiometers buried 0.10 m deep near the QICs. Using these readings the set point of the QIC potentiometer was verified to match the target set points of 10 and 25 kPa. It is important to note that QICs were checked weekly for proper operation but the set-points were not adjusted for the remainder of the season.
An independent set of dielectric probes (0.20 m ECH20 probe, Decagon Devices, Inc., Pullman, WA) connected to individual dataloggers (HOBO H08-006-04, Onset Computer Corporation, Pocasset, MA) was installed vertically in the top 0.20 m next to the switching tensiometers and QIC probes. Soil water content was recorded hourly from these 16 probes and average seasonal values for each treatment were calculated.

No. 4. Influence of various crops in rotation on population of soil nematodes.
Experimental conditions
The pot experiment was conducted in a screen house from June 2002 to February 2003 at Tropical Research and Education Center, University of Florida, Homestead, Florida, which is in a subtropical region. The average annual rainfall is 1,499 mm of which 76% falls between June and October; the annual temperature averages 23.9 oC and usually ranges from a maximum of 35 oC in June to a minimum of 5 oC in January (Wang et al., 2002). Between June 2002 and February 2003, the air temperature ranged from a minimum of 2.2 oC to an average monthly maximum of 34.6 oC; the monthly average maximum temperature was 35.3 oC in August 2002 but only 28.5 oC in January 2003; and the relative humidity ranged between 75% in January to 84% in June (Wang et al., 2006).
The soil (loamy-skeletal, carbonatic, hyperthermic Lithic Udorthents) contained 58.8% gravel (> 2mm), and the non-gravel fraction had a distribution of soil particles of 48.4% sand, 30.3% silt and 21.3% clay. The soil also consisted of 60% calcium carbonate (CaCO3), pH 7.8, soil organic C 28 g kg-1, total N 1.1 g kg-1, and ammonium bicarbonate-diethylene triaminepentaacetic acid (AB-DTPA) extractable phosphorus (P) 22.7 mg kg-1 and potassium (K) 129 mg kg-1, respectively.

Experimental design and management
A complete randomized block design with 8 different rotation schemes of the given crops was adopted. The 8 crops were marigold I (MI), marigold II (MII), radish, Raphanus sativus L. var. sativus (RD), Indian mustard, Brassica juncea (L.) (IM), sunn hemp (SH), cowpea [Vigna unguiculata (L.)] (CP), velvetbean (VB) and okra (OK). There were three rotations in each scheme, i.e. MI-RD-MI, MII-CP-MII, IM-VB-IM, RD-MI-RD, SH-OK-SH, VB-IM-VB, CP-MII-CP, and OK-SH-OK, respectively. Each treatment was replicated 3 times. Before the experiment started and after each rotation, a 250 ml soil sample was collected from each pot to identify and count the nematodes.
Prior to the experiment, tomato roots replete with root galls caused by the root-knot nematode were collected from a commercial farm, cut into small pieces (< 1 cm) and this inoculum was blended into the potting soil. A very nematode-susceptible plant, okra was seeded then and grown for 4 weeks to increase the root-knot nematode population since the initial population of root-knot nematodes in this soil were fairly low (Wang et al., 2003). After 4 weeks the okra plants were harvested and their roots replete with root galls produced by the female root-knot nematode, Meloidogyne incognita, were cut into pieces 1-cm long and evenly distributed into the soil. The soil was mixed well and 3 kg of it was placed into each pot, which was 6 cm in diameter and 15 cm high with a capacity of 1.5 liter. The soil was sieved to remove large gravel (> 1 cm). The crops were first seeded on June 6, 2002 to produce 3 plants per pot for velvetbean, 5 for cowpea, radish, Indian mustard, and 10 for the others. Drip irrigation was installed and adjusted to deliver 2 L water per hr. and a clock timer was used to control automatically the irrigation duration and frequency based on the plant growth stages. Each succeeding rotation was started immediately after the roots had been rated and the roots, stems and leaves cut into 2-cm long pieces and incorporated into the soil in same pot used for the previous rotation. Each rotation lasted about 3 months.

Sampling and analysis
Roots were washed free of soil and examined for galling and root knot infection. Some roots showing lesions were cut into small pieces and left in water for 36 to 48 hr to reveal the presence of any lesion and other nematodes. Root galling was rated after each rotation on a 0-5 scale (Taylor et al., 1978). Each 250-ml soil sample was collected from 3 to 12 cm below the surface in each pot. Nematodes from each sample were extracted by means of Cobb’s sieving and decanting technique (Cobb, 1918), followed by a modified Baermann funnel method (Hopper, 1986). Sieves used in nematode extraction were U.S. Standard Sieve Series of 100, 200, and 325 mesh with openings of 149, 74, and 44 m, respectively. Nematodes were fixed in hot 30 ml/L formaldehyde solution, identified to genus level, and counted using a stereoscope. Some fixed specimens were processed with anhydrous glycerin (Seinhorst, 1959), and examined under a compound microscope for species identification. Nematode identifications were based on the morphology of adult and larval forms and their identities were confirmed with recent taxonomic keys (Handoo et al., 1992; Mai et al., 1996; Maqbool, 1982; Robinson et al., 1997; Sher, 1996). Nematode density (number in 250 ml of soil) was determined for each species and recorded.

Data analysis
The data were subject to the analysis of variance (ANOVA) and Duncan’s multiple range test with a general linear model (GLM) for significant differences using SAS (version 8.1, SAS Inst. Inc., Cary, NC, USA).

No. 5. Influence of cover crops in rotation on improving okra (Abelmoschus esculentus L.) yield and suppressing parasitic nematodes.
Site description
The experiment was conducted at the Tropical Research and Education Center, University of Florida, Homestead, Florida. At this site the average annual rainfall is 1,499 mm of which an average 76% falls between June and October, the annual temperature averages 23.9 oC and usually ranges from a maximum of 35 oC in June to a minimum of 5 oC in January (Wang et al., 2002a). The soil is a Krome very gravelly loam (loamy-skeletal, carbonatic, hyperthermic Lithic Udorthents), which consist of 58.8% gravel (> 2 mm), and a gravel-free fraction. The latter consists of 48.4% sand, 30.3% silt, and 21.3% clay. CaCO3 comprises about 60% of the soil, organic C is 11.3 to 18.0 g kg-1, total N is 0.9 to 1.3 g kg-1, the soil pH is 7.6 to 7.8 (water), ABDTPA (ammonium bicarbonate-diethylene triaminepentaacetic acid) extractable phosphorus (P) and potassium (K) are 16.5 to 26.8 mg kg-1 and 123.5 to 132.6 mg kg-1, respectively.

Experimental design and management
The field experiment was conducted in three consecutive years from 2002 through 2005 using a randomized split-plot design. The main plots consisted of four cover crops, sunn hemp, velvetbean, cowpea and sorghum sudangrass, grown from June to September, and fallow as a control, and all plots were on raised beds. In the first year compost was applied as an organic mulch (OM) to some plots at the single rate of 50 t ha-1 dry weight, while white on black plastic mulch (PM) was installed on others. In the second and third years, the 50 t ha-1 treatment was applied to the very same plots as in the first year of the experiment, and three additional compost treatments were made, i.e., 25 t ha-1, 50 t ha-1, and 75 t ha-1. Thus the four organic mulch treatments are denoted as OM1-25, OM1-50, OM1-75, and OM2-50 in the second year and as OM2-25, OM2-50, OM2-75, and OM3-50 in the third year, respectively.
The seeding rates of cover crops were 56 kg ha-1 for sunn hemp, 112 kg ha-1 for cowpea, 45 kg ha-1 for both velvetbean and sorghum sudangrass. In order to promote branching and increase the production of high quality biomass, the apical dominance of the sunn hemp was overcome by cutting the stems at 30 cm above the ground in the middle of August (Abdul-Baki et al. 2001.). The cover crops were terminated by flail-mowing, incorporated into the soil in mid September each year. Early in October, 1120 kg ha-1 of dry fertilizer (6 N-6 P2O5-12 K2O) was rototilled into the soil together with the cover crop residues. Then the raised beds 15-cm high, 91-cm wide and 182-cm between centers of two adjacent beds were re-formed. Compost was supplied to the appropriate plots by means of tractor-powered calibrated spreader. Each plot consisted of a 15-m long section of a raised bed, which was 27 m2. Two parallel T-tapes, each 18 cm from the center of the bed were installed and connected to a layflat hose, which provided the water for drip irrigation. Tomato (Lycopersicon esculentum (Mill.)) ‘Sanibel’ in 2002, and ‘Florida 47’ in 2003 and 2004, respectively. Seedlings were transplanted into in a single row on each bed with 50-cm between plants. Practices to control foliar insects and diseases were applied according to Maynard and Olson (2000). Each year starting from the sixth week after tomato transplanting, 328 l ha -1 of liquid fertilizer consisting of 4 N-0 P2O5-8 K2O was delivered through the drip lines once per week until the second harvest.

Harvests and grading
Tomato fruits were harvested three times each year. The first harvest was conducted when about 10% of fruits had turned red, and only red or pink, and extra large green and large green fruits (“mature green” fruits) were harvested during this time. Two or three weeks later, the second harvest was similarly performed. Finally 3 or 4 weeks after the second harvest, the third harvest was conducted, which included all fruits equal or larger than the small size. Harvested fruits were separated by machine (Kerian speed sizer, Kerian Machine, Inc., Grafton, ND) according to the Florida Tomato Committee Standards (Brown, 2000) into extra-large, large, and medium and small sizes. Defective fruits were culled manually. The fruits in each size category as well as the culls were weighed. Extra-large, large, and medium fruits constituted the marketable yield, and the small and culled fruits constituted the non-marketable yield.

Sampling and analysis
Soil samples (0-10 cm in depth) were collected before the cover crops were seeded, after the cover crops had been soil-incorporated but before tomato seedlings were transplanted and at tomato flowering. Above ground biomass samples of the cover crops were collected each year before they were terminated by flail-mowing. At the flowering, the height and canopy diameter of each of 5 randomly selected tomato plants from each plot were measured and the canopy area was calculated. The chlorophyll content of the third fully expanded leaf from the top of each of these same tomato plants was determined with a SPAD-502 meter, and then this leaf was collected for further analysis.
Soil samples were air dried and ground to pass through a < 2 mm mesh sieve. Plant biomass samples were oven dried at 70 oC for >72 hr before being ground to pass through a <1 mm mesh sieve for chemical analysis. Total N of soil and plant samples was determined with a CNS auto-analyzer (Vario Max Elementar, Hanau, Germany). Soil organic carbon was determined by the weight loss-on-ignition (WLOI) method (Schulte and Hopkins, 1996; Jolivet et al., 1998). In order to determine the total nutrient elements other than N, the samples were digested with concentrated nitric acid-hydrogen peroxide-hydrochloric acid (HNO3-H2O2-HCl) according to the USEPA method, 3050A (USEPA, 1990), then analyzed via inductively coupled plasma optical emission spectroscopy [ICP-OES (Ultima 2C) Horiba Jobin Yvon Inc., Edision, N.J.]. Soil sub-samples were extracted with AB-DTPA for colorimetric determination of extractable P, and for ICP-OES determination of extractable K. The composition and properties of compost used in the experiment were determined with the methods used for the soil samples, and the data were summarized in Table 1. At the end of the third year, soil physical properties, e.g., soil bulk density (Blake and Hartge, 1986), field capacity and hydraulic conductivity (Jury and Horton, 2004), etc. were determined. Statistics
By means of the SAS program (SAS Institute, version 8.1, Cary, N.C.), the data were subjected to ANOVA and the means were separated using Duncan’s multiple range test.

No. 6. Influence of cover crops and soil amendments on okra production and soil nematodes.
Pot size and soil properties
The growth media were placed in 8.3-L plastic pots each 23 cm in diameter and 20 cm high with a capacity of 8 kg of soil per pot. The soil was Krome very gravelly loam (loamy-skeletal, carbonatic, hyperthermic Lithic Udorthents) collected from a field in the Tropical Research and Education Center. The soil contained 58.8% gravel (>2mm), had a distribution of soil particles of 48.4% sand, 30.3% silt and 21.3% clay. Also the soil contained 60% CaCO3, pH 7.8 (water), soil organic C 28 g kg-1, total N 1.1 g kg-1, and AB-DTPA extractable P 22.7 and K 129 mg kg-1, respectively. Since the densities of Meloidogyne incognita root-knot nematode population in fields of the Tropical Research and Education Center were known to be quite low (Mannion et al. 1994), roots of tomatoes with galls were collected from several farms in Miami-Dade County, and pieces of these roots were added to the soil in the pots.

Cover crops and organic soil amendments
Summer cover crops, sunn hemp (Crotalaria juncea L.), and sorghum sudangrass [Sorghum bicolor × S. bicolor var. sudanense (Piper) Stapf.] were grown to compare their effects on okra yield and nematode population densities with those of fallow as a control. Organic amendments incorporated into the soil were biosolids, N-viro soil (1:1 mixture of coal ash and biosolids), coal ash, co-compost (3:7 mixture of biosolids and yard wastes), yard waste compost (YW-compost), control (cover crop grown and incorporated into the soil, but without any other organic amendment), cover crop removal (the cover crop was grown until the flowering stage when the aerial parts and most of the roots were removed and discarded), and cover crop + MC-33 (the cover crop was grown and incorporated into the soil, and subsequently fumigated with a mixture of 33% of methyl bromide and 67% of chloropicrin). The amount of each organic amendment added to the soil in each pot was 205 g of dry weight equivalent; which was equivalent to 50 Mg ha-1. After the cover crops residues and/or organic amendments had been incorporated into the soil, the amended soil was allowed to equilibrate for 10 days before the okra was seeded. The composition and properties of the various organic amendments were determined and are summarized in Table 1. More detailed information can be found in Wang et al. (2003b). The experiment was carried out from June 2002 to February 2003 as the first year (Year-1), and June 2003 to February 2004 as the second year (Year-2).

Experimental design and management
In order to determine the effectiveness of sorghum sudangrass, and sunn hemp relative to fallow in suppressing various taxa of nematodes an experiment was conducted using a randomized complete block design with three replicates. Subsequently to determine the relative efficacy of combinations of cover crops and various inanimate organic amendments a split plot design with 3 replicates was employed in which the two cover crops were the main plots, and the organic amendment were subplots. In order to keep the size of the experiment manageable, fallow was not included as a main plot. When the cover crop had developed to the onset of flowering, the aerial parts were cut into pieces (< 2 cm) and then thoroughly mixed into the soil from the pot together with the appropriate organic amendment if any. This mixture was returned into the same pot. In the MC-33 treatment, the pots in which the cover crop had been soil incorporated were fumigated by placing them into a chamber and using liquid N to introduce the appropriate amount of the 33% methyl bromide-67% chloropicrin mixture. The chamber was kept hermetically sealed for 72 hours. Thereafter the pots were exposed to the atmosphere for an entire week, and then okra (Abelmoschus esculentus L.) was seeded in each pot. The okra planting was thinned at the 3-leaf stage to 6 plants per pot. Drip irrigation was installed and adjusted to deliver 2-L hr--1 of water. A clock timer was used to control the irrigation automatically. The period and frequency of irrigation were adjusted according to needs of the successive plant growth stages. Okra fruits were harvested when they attained full development. Sampling and analysis
Each cover crop was sampled for biomass determination at the time of termination. Okra fruits were harvested to obtain the fruit yield. The okra yields and cover crop biomass weights were converted to metric tons per hectare (Mg ha-1) equivalent according to the surface area of the pot. For determining the identities and densities of the various nematode taxa, soil samples were collected before the cover crops were seeded and after their termination, and also after the okra harvest. A soil sample of 250 ml was taken from each pot. Nematodes from each sample were extracted by means of Cobb’s sieving and decanting technique (Cobb, 1918), and the modified Baermann funnel method (Hooper, 1986). Sieves used in nematode extraction were U.S. Standard Sieve Series of 100-, 200-, and 325-mesh with openings of 149, 74, and 44 m, respectively. Nematodes were fixed in hot 30ml•L-1 formaldehyde solution, identified to genus level, and counted using a stereoscope. Some fixed specimens were processed with anhydrous glycerin (Seinhorst, 1959), and examined under a compound microscope for species identification. Nematode identifications were based on the morphology of adult and larval forms and their identities were confirmed with recent taxonomic keys (Handoo and Golden, 1992; Mai et al., 1996; Sher, 1966; Handoo, 2000). Roots were washed free of soil and examined for galling and root knot infection. Some roots showing lesions were cut into small pieces and left in water for 36 to 48 h to reveal the presence of any lesion and other nematodes. Nematode density (number in 250 ml of soil) was determined for each species and recorded. The okra plants were individually rated for root galls and egg masses on a 0-5 scale: 0 = 0 galls, 1 = 1-2, 2 = 3-10, 3 = 11-33, 4 = 31-100, 5> 100 galls or egg masses (Taylor and Sasser, 1978). The data were subjected to the analysis of variance (ANOVA) and Duncan’s multiple range tests for a significant difference by means of SAS (version 8.1, SAS Inst. Inc., Cary, NC, USA).

No. 7. Summer Cover Crops and Soil Amendments to Improve Growth and Nutrient Uptake of Okra.
Soil properties and experimental design.
The experiment was conducted in pots of 8.3-L each, 23 cm in diameter and 20 cm high with a soil capacity of 8 kg/pot. The soil was a Krome very gravelly loam (loamy-skeletal, carbonatic, hyperthermic Lithic Udorthents) collected from a field in the Tropical Research and Education Center, University of Florida, Homestead, FL. The soil contained 58.8% gravel (>2 mm sieve), had a distribution of soil particles of 48.4% sand, 30.3% silt and 21.3% clay. Also the soil contained 60% calcium carbonate (CaCO3), pH 7.8 (water), soil organic C 28 g•kg-1, total N 1.1 g•kg-1, and ammonium bicarbonate-diethylene triaminepentaacetic acid (AB-DTPA) extractable phosphorus (P) 22.7 and potassium (K) 129 mg•kg-1, respectively.
A split plot design was used in which the main plots were four summer cover crops and fallow, and the subplots were five organic soil amendments along with a no amendment control. When the cover crop, sunn hemp, reached the optimum stage for termination (flowering), the stems of all the cover crops were cut off at ground level and cut into pieces about 2 cm long and thoroughly mixed into the soil together with the appropriate organic amendment if any. After these soil amendments were applied, the materials in the pots were allowed to equilibrate for 10 d before the okra was seeded. The experiment was carried out in a screen house from Jun. 2002 to Feb. 2003 of the first year (2002-03), and Jun. 2003 to Feb. 2004 of the second year (2003-04).
The main treatments were summer cover crops, sunn hemp, cowpea, velvetbean, and sorghum sudangrass and a weedy natural fallow as the control. The subplot treatments were soil amendments: biosolids, N-Viro Soil (N-Viro International Corporation, Toledo, Ohio), coal ash (a byproduct from power plants in Fla.), co-compost (3:7 of biosolids to yard wastes, West Palm Beach, Fla.), yard waste compost (mainly from leaves and branches of trees and shrubs, and grass clippings), and a control (soil-incorporated cover crop residues but without any organic amendment). Each soil amendment was applied at 205 g/pot of dry weight equivalent, which was equivalent to 50 Mg•ha-1. The composition and properties of the various organic amendments were determined and are summarized in Table 1.
Okra seeds were sown on Aug. 20 and 25 of years 2002 and 2003, respectively, and thinned at the three-leaf stage to six plants per pot. Drip irrigation was installed and adjusted to deliver 2 L•h-1 of water. A clock timer was used to control the irrigation automatically. The period and frequency of irrigation were adjusted according to needs of the successive plant growth stages. Okra fruits were harvested twice each week for seven weeks started on Jan. 5, 2003, and Jan. 10, 2004, respectively. At the end of the experiment, to obtain the total biomass, the remaining fruits, shoots and roots washing free of soil were harvested. Plants were separated into fruits, stems and roots, and random samples of these plant parts were taken for chemical analysis to determine concentrations of B, C, Cd, Cu, Fe, K, Mg, manganese (Mn), Mo, N, P and Pb. Carbon and N were analyzed with a carbon-nitrogen-sulfur (CNS) Auto-analyzer (vario Max Elementar, Hanau, Germany), and all the other elements were analyzed via inductively coupled plasma optical emission spectroscopy (ICP-OES, Ultima 2C, Horiba Jobin Yvon Inc., Edison, N.J.) after the samples had been digested with concentrated nitric acid-hydrogen peroxide-hydrochloric acid (HNO3 – H2O2 – HCl) according to the U.S. EPA Method 3050A (1990).
After the okra plants were harvested and removed, sorghum sudangrass was grown in the same pots to study the residual effects of the cover crops and soil amendments. Twenty five sorghum sudangrass seedlings were grown in each pot and irrigated as above. The sorghum sudangrass was grown from Nov., 2002 to Jan., 2003, then removed from the pots, dried at 70 oC for 72 h and weighed to obtain the aboveground dry biomass.

Sampling and analysis.
The cover crops were sampled for biomass determination at the time of their termination. Also a representative okra plant from each pot was sampled at the visible bud (pre-flowering) stage to determine the dry weight of its biomass. Okra fruits, shoots and roots (washed free of soil) were sampled. Soil samples were collected before and after growing the cover crops and also after the okra harvest.
The plant samples were dried at 70 oC for 72 h and ground to pass through a 1-mm sieve. Soil samples were air-dried, plant materials were removed, and the samples were gently ground by hand to pass through a 2-mm sieve. Soil samples were extracted with AB-DTPA for P, K, Ca, Mg, and micro-nutrient element analysis via ICP-OES. Total N and C in both soil and plant samples were determined via a CNS Auto-analyzer. Soil organic carbon was determined by the weight loss-on-ignition (WLOI) method (Schulte and Hopkins 1996).
The data were subjected to the analysis of variance (ANOVA) and Duncan’s multiple range tests for significant differences using SAS (version 8.1, SAS Inst. Inc., Cary, NC, USA).

No. 8. Conservation of soil and nutrients by cover crops under high and low rates of simulated rainfall.
Cover crops chosen and soil properties
Three legume summer cover crops, sunn hemp (Crotalaria juncea), cowpea (Vigna unguiculata), velvetbean (Mucuna deeringiana) and a non-legume, sorghum sudangrass (Sorghum bicolor × S. bicolor var. ‘sudanense’) were cultivated in pots with Krome very gravelly loam soil (loamy-skeletal, carbonatic, hyperthermic Lithic Udorthents) in a screenhouse from Jul. through Oct., 2002. The soil contained 29.2g kg-1 of organic C, 982.3 mg kg-1 of total N, 46.8 mg kg-1 of AB-DTPA extractable P and had a pH (KCl) of 8.2 and a CaCO3 content of 682 g kg-1. The soil contained 58.8% of gravel (>2 mm) and particle distributions in the gravel free soil were 40.8% sand, 39.7% silt, and 19.5% clay. Each pot was 18 cm in diameter, 30 cm deep and had a capacity of 8 kg soil. The soil was thoroughly mixed and then placed into each pot. Plant density per pot was as follows: 30 sunn hemp plants, 5 sorghum sudangrass plants, 5 velvetbean plants or 5 cowpea plants. Each treatment was replicated four times.

Water supply and leachate collection
Sprinkler heads with a tubing system to deliver water at 4 L hr-1 (high rate) and 2 L hr-1 (low rate), equivalent to average rainfall amounts of 5.8 mm week-1 and 11.6 mm week-1, respectively, were installed. Graduated beakers were kept among the pots for monitoring the amount of water actually delivered, and hence, facilitate efforts to ensure uniform delivery to each pot. From the third week after cover crops had been sown, a plastic saucer was placed under each pot to receive the leachate (gravitational water) and, a PVC cylinder, 10 cm in diameter and 5 cm high, was placed between the pot and the saucer to prevent the percolation from soaking the soil at the bottom of the pot. The amount of water and frequency of application were adjusted according to plant growth periods, and the system was automatically controlled with a clock timer (Hose Faucet, model 62001/62401) installed on a water tap. The amounts of water supplied and leachate collected were recorded daily. Leachate samples were collected weekly for chemical analysis. To enable the sorghum sudangrass to establish but to keep each cover crop uniform in all treatments, fertilizer (10 N-10 P2O5-10 K2O) at a rate equivalent to 771 kg ha-1 was applied to each pot at the end of the first week of leachate collection. The fertilizer contained 2.0% NO3-N, 6.0% NH4-N, 1.8% other /water soluble N or urea N and 0.2% water insoluble N, 10% available phosphate (P2P5), 10% soluble potash (K2O) and some microelements.

Sampling and analysis
Soil samples were taken before the experiment, ground to pass < 2 mm sieve for chemical analysis. The stems of all the cover crop plants were cut off at soil surface when the sunn hemp reached its blossom stage. The roots were washed free of soil, and the stems were separated from the leaves. The plant parts were dried at 70 oC for 72 hours to obtain the dry weight of the biomass. The leachates were filtered before the chemical analyses were carried out using a colorimetric method via an Auto-Analyzer-3 (BRAN-LUEBBE, Germany). The detection limits for the equipment were 0.02 mg l-1 for NO3-N, 0.01 mg l-1 for NH4-N, and 0.002 mg l-1 for inorganic P, respectively. Soil and plant N were analyzed by means of CNS Auto-analyzer (vario Max Elementar, Hanau, Germany).
To investigate the movement of soil particles and their redistribution as influenced by various cover crops under low- and high-rates of simulated rainfall, an intact core column sample was collected from the center of each pot after the harvest of the cover crops. Each core column was sliced into 0-10 cm, 11-20 cm, and 21-30 cm segments, respectively. The soil samples were air dried and the particle distribution analysis was conducted using the micro-pipette approach (Miller and Miller, 1987). The same procedures were conducted on the soil mixture initially used to fill the pots.

Statistics
The data were subjected to the analysis of variance (ANOVA) and Duncan’s multiple range tests via SAS program version 8.11, SAS Inst. Inc., Cary, NC, USA.

No. 9. Joint use of organic and plastic mulch to improve bell pepper production in a subtropical region (manuscript not prepared).
Experimental site and primary conditions
Experiments were conducted at commercial farm, Pine Island Farms (PIF), located 22 miles northeast of Homestead, FL and at the Tropical Research and Education Center (TREC), University of Florida, Homestead, FL, The soil at PIF is a very sandy and calcareous soil and that TREC is Krome very gravelly loam soil with low soil fertility and is pH 7.8 (Table 1).

Experimental design and treatments
At Pine Island Farms, the land was used for commercial winter fresh market vegetable production. The previous crop was tomato grown from October through March, and the TREC site had been fallow. On both sites a conventional cover crop, sorghum sudangrass was seeded in a rate of 45 kg/ha and grown from June through August. After the cover crop had been flail-mowed and incorporated into the soil, raised beds each 3 ft wide, 8 in high with 3 ft-wide aisles between adjacent beds were made.
The following five treatments at both sites were 1) organic mulch plus plastic mulch, 2) herbicides, Devrinol and Dual Magnum, applied to organic mulch on the bed, which was then covered with plastic mulch, 3) herbicides, Devrinol and Dual Magnum, applied to the organic mulch on the bed, 4) fumigation of the bed with a mixture of methyl bromide (33%) and chloropicrin (67%) (MC33); the bed was then covered with plastic mulch, and 5) plastic mulch alone as a control. Dual Magnum at 1.78 l/ha and Devrinol powder at 4.5 kg/ha were sprayed on the surface of corresponding beds. Soil fumigation was accomplished by injecting 312 kg/ha of MC-33 into the appropriate beds. Compost at 50 t/ha dry weight equivalent was delivered and evenly spread on the surface of the appropriate beds. Two drip irrigation lines were installed just before covered the plastic mulch.
Bell pepper (Capsicum annuum, cv. ‘Cascade’) was transplanted in two rows on each bed with 30 cm between two adjacent and 45 cm between the two rows. Liquid fertilizer with a formula of 4-0-8 (N-P2O5-K2O) was injected through the drip lines twice per week at 1.1 kg/ha/day prior to fruiting and at 2.2 kg/ha/day after the onset of fruiting.
Peppers were harvested five times from each plot and graded according to the USDA standard.

Virginia Component
No. 10. Using high-residue cover crop mulch for weed management in organic no-till potato production systems.

Research. In order to develop the potato production systems, a split plot, randomized block experiment with four replications will be conducted on 16 raised beds, 40-m long at the Kentland Agricultural Research Farm (KARF), located near Blacksburg, VA. Main plots will be 10-m sections across four beds consisting of ground covers: A = no cover (control); B = sorghum sudangrass; C = a mixture of sorghum sudangrass and sunn hemp; and D = a mixture of spring oats and cowpeas. Subplots within each main plot will be weed management methods: 1 = no herbicides applied; and 2 = pre-emergence herbicides (S-metolachlor and Linuron) applied.
Main plot ground covers will be drilled on preformed raised beds (2 m wide and 20 cm high) in August 2003 and 2004. Appropriate organic fertilizers and irrigation water (if needed) will be applied to achieve production of high levels of weed-free ground covers. The winter-killed cover crops (treatments B, C, and D) will be left undisturbed until potato seed pieces are planted in early April 2004 and 2005. Healthy 40-60 g seed pieces will be placed 10-12-cm deep in the raised beds using the Subsurface Tiller-Transplanter (SST-T) (Morse et al., 1993). Drip tubing will be laid and organic fertilizer applied in row at planting with the SST-T. Additional soluble organic fertilizer (foliar or applied through the drip tubing) will be applied as needed based on leaf-sap nitrate testing during the growing season.
Data collected will include the following: tuber yield, graded according to USDA standards; weed biomass taken at 5 and 8 weeks after planting; and nematode and Colorado potato beetle populations taken at 6, 9 and 12 weeks after planting.

Dissemination (outreach) plan. Four methods will be used to disseminate the knowledge and results gained from this study and previous research at KARF. First, two on-farm grower demonstration plots will be established each year of this study. Second, field days will be hosted at the on-farm demonstration sites. Third, presentations will be given at county and multi-county extension meetings and at the annual meeting of the Virginia Association for Biological Farming (VABF). Fourth, various materials including an extension leaflet will be prepared and distributed electronically as well as in printed form.
Demonstration plots will be established on the farms of two organic growers (Warren LaForce and James Fannon). In August of 2003 and 2004, raised beds will be erected and seeded with an appropriate cover crop mixture, as determined in consultation with the grower and from previous research conducted at KARF during the past eight years. In April of 2004 and 2005, ‘Kennebec’ potato seed pieces will be planted with the SST – T; production practices and data collection will be followed similar to that used in the research at KARF.

Relevant Literature
Belair, G. and L.E. Parent. 1996. Using crop rotation to control Meloidogyne hapla Chitwoud and improve marketable carrot yield. HortScience 31(1): 106-108.
Bellinder. R.R. and R.W. Wallace. 1991. An integrated production management approach to weed control in potatoes, p. 677-687. In: D. Pimental (ed.). CRC Handbook of pest management in agriculture, 2nd Edition, Vol. III.
McSorley, R. 1998. Alternative practices for managing plant parasitic nematodes. American Journal of Alternative Agriculture 13 :98-1 04.
Morse, R.D. 1999. Mechanical methods of killing cover crops for high-residue/no-till production of transplanted broccoli (Brassica oleracea L. gp. 1talica). Acta Horticulturae, 504: 121-128.
Morse, R.D. 1997. No-till production of Irish potato on raised bed, p. 117-121. In: R.N. Gallaher and R.M. McSorley (eds.). Proc. Southern Conservation Tillage Conference for Sustainable Agriculture, Gainesville, FL.
Morse, R.D., D.H. Vaughan and L.W. Belcher. 1993. Evolution of conservation tillage systems for transplanted crops; potential role of the Subsurface Tiller Transplanter (SST – T), p. 145-151. In: Billich P.K. (ed). Proc. Southern Conservation Tillage Conference for Sustainable Agriculture, Monroe, LA.
Wyman, J .A., J. Feldman and S.K. King. 1994. Cultural control of Colorado potato beetle: Off-crop management. p. 376-385. In: G.N. Zehnder, M.L. Powelson, R.K. Jansson, and K.V. Raman (Eds.). Advances in Potato Pest Biology and Management. APS Press, St. Paul, Minnesota.

Research results and discussion:

No. 1. Biologically-based tomato production system*.
A three year-experiment was conducted near Homestead, Florida to evaluate the feasibility of using a biologically-based system for winter production of fresh-market tomatoes (Lycopersicon esculentum Mill.) in south Florida fields with light to moderate infestations of the root knot nematode, Meloidogyne incognita, and yellow nutsedge, Cyperus esculentus. The experiments were conducted at two locations: the Tropical Research and Education Center (TREC) at Homestead in 2001/02 and 2002/03 and at Pine Island Farms (PIF), 20 miles northeast of Homestead, in 2004. The system consisted of a cropping rotation in which nematode-resistant cover crops [cowpea (Vigna unguiculata cv. Iron Clay), velvetbean (Mucuna deeringiana), and sunn hemp (Crotalaria juncea cv. Tropic Sun)] were followed by ‘Sanibel’, a nematode-resistant tomato cultivar in 2001/02, ‘Leila’, a nematode-susceptible cultivar in 2002/03, and ‘Agri 6153’, a Fusarium and Verticillium-resistant, nematode-susceptible indeterminate cultivar developed for vine-ripe production in 2003/04. There were two cover crop treatments (cowpea and velvetbean) and a standard methyl bromide/chloropicrin (MC-33) treatment in 2001/02. A third cover crop treatment using sunn hemp was added in 2002. In 2003/04, two cover crop treatments (velvetbean and sunn hemp), a fallow (no cover crop), and a MC-33 treatment preceded by a summer sorghum sudangrass cover crop, were used. Each treatment was replicated four times in all years. Biomass production by the velvetbean, cowpea, and sunn hemp averaged 14.8, 8.5, and 11.6 Mg ha -1, respectively.
Suppression of root-knot (Meloidogyne incognita) nematode by the cover crops could not be rigorously determined because of a very low density nematode population at TREC and a low –to-moderate populations at Pine Island Farms.

Table 1. Effects of cover crops and soil fumigant on root-knot (Meloidogyne incognita) nematode densities prior to treatment, before tomato transplanting, and after tomato harvest, and on root health after harvest at Pine Island Farms in 2003/04 winter production season.

Treatment
No. root-knot nematodes / 150cm3 soil
Root-knot nematode gall rating after tomato harvest Root-rot rating after tomato harvest
Before
treatment Before tomato transplanting
After tomato harvest
Velvetbean 13.8 a z 10.4 a 59.9 a 2.7 a y 0.27 ax
Sunn hemp 12.8 a 12.2 a 72.1 a 3.2 a 0.38 a
Fallow 19.2 a 10.6 a 68.1 a 3.2 a 0.20 a
MC-33 11.7 a 9.8 a 61.8 a 3.6 a 0.13 a

z Values in the same column followed by the same letter are not significantly different (P  0.05) according to Duncan’s multiple range test.
yRoot-knot nematode gall rating on a 0-5 scale: 0=0 galls;
1 = 1-2; 2 = 3-10; 3 = 11-30; 4 = 31-100; 5 => 100 galls or egg masses (Taylor and Sasser, 1978).
x Root rot rating on a 0-5 scale: 0 = no necrosis; 1 =< 33%; 2 => 33 to < 66%;
3 => 66% <= 100%; 4 = dead major root; and 5 = dead plant (Coyler, 1988). Tomato marketable yields in all treatments and in all years were above average annual yields in Miami-Dade County. Yields were highest in 2003/04 because the crop was healthy and the prices favored eight harvests. In contrast, yields were low in 2002 due to a heavy infection by foliar pathogens. In 2001/02, there was no significant difference in extra-large fruit yield among the treatments but the MC-33 treatment yielded higher large fruits than the cowpea and velvetbean treatments thus resulting in a higher total marketable yield than both cover crop treatments. The total marketable yield in the velvetbean treatment was next highest. In 2002/03, the cowpea treatment yielded significantly higher extra-large fruits than the MC-33 and the velvetbean treatments and significantly higher total marketable yield than all other treatments. In 2003/04, sorghum sudangrass / MC-33, velvetbean, and sunn hemp treatments had equal marketable yields in all fruit-size grades and were significantly higher than the fallow treatment. Table 2. Yields of extra large, large, medium, and total marketable tomatoes cv. ‘RTF 6153 grown under conventional and cover cropping systems at the Pine Island Farms during 2003/04 winter production season. Treatment Year
Grade
Sorghum sudan/MC-33
Velvetbean Sunn hemp Fallow

2004

—————————-Yield (Mgha-1)——————-

Extra-large 56.58 abz 55.59 ab 66.15 a 45.06 b
Large 25.32 a 24.42 a 23.09 a 15.98 b
Medium 5.40 a 5.11 a 4.02 a 4.64 a
Total 87.30 a 85.42 a 93.26 a 65.68 b

zValues within the same row followed by the same letter are not significantly different (P  0.05) according to Duncan’s multiple range test.

Economic analysis shows that all treatments resulted in positive net returns in all years. Returns in 2003/04 were the highest of all study years due to high yields and high market prices. Among the cover crops, sunn hemp produced the highest yields and net returns of all treatments over the two years it was used.

Table 3. Economic summary of tomato production under alternative cover crop systems, in years 2001/02, 2002/03, 2003/04 (in $/ha, rounded to the nearest $10).
Net Returns
Treatment Year 1 Year 2 Year 3
Fumigation with MC-33 $16,930 $3,150 $41,020
Cowpea $12,030 $7,110 ______
Velvetbean $15,310 $5,190 $41,740
Sunn hemp _______ $7,930 $47,560
Fallow _______ ________ $28,860
Note: this is an extract from Table 6 in Publication No. 1, Abdul-Baki, et al., 2005.

*Note: This experiment was initiated in 2001 without the benefit of support from SARE Project# LS03-148. When the latter grant was approved, this project was continued and expanded.

No. 2. Use of summer cover crops and organic mulch to improve tomato yields and soil fertility.

Summer cover crops were grown and incorporated as green manures into the soil, which was formed into raised beds covered either with plastic or with an organic mulch of compost applied at different rates of composts. The purpose was to investigate the effects of these treatments on tomato (Lycopersicon esculentum Mill.) yield and soil fertility. The treatments in this experiment were repeated for three consecutive years at Homestead, Florida, which lies in a subtropical region. The summer cover crops were sunn hemp (Crotalaria juncea L. cv. Tropic Sun), velvetbean, Mucuna pruriens var. utilis (Wall. ex Wright) Baker ex Burck, cowpea (Vigna unguiculata L., cv. Iron Clay) and sorghum sudangrass (Sorghum bicolor × S. bicolor var. sudanense (Piper) Stapf.) versus a natural fallow as a control.
The cover crops were flail-moved and incorporated into the soil. In the 1st year, 50 t/ha of compost was applied as an organic mulch versus plastic mulch (PM). In the second year, this same application rate of compost was used on the same plots as in the first year, and three more rates were applied on other plots, i.e., 25 t/ha, 50 t/ha and 75 t/ha. In the 3rd year, compost at the same rates as in the second year was again applied on the same plots as in the 2nd year. Again for comparison, plastic mulch, the conventional treatment, was applied to the same beds as in the previous two years. Each year in the fall after the cover crop residues had been incorporated into the soil and after the organic and plastic mulches had been applied, a fresh market cultivar of tomato were transplanted into the beds, and harvested in the winter.
Among the cover crop treatments, the sunn hemp treatment produced the highest tomato yields. The effect of organic mulch on marketable tomato yields in the first year was similar to that of sunn hemp. The repeated application of organic mulch at 50 t ha-1 in each of two or three consecutive years significantly increased tomato yields over the application of organic mulch at the low rate of 25 t/ha, in one or two consecutive years. Yields of extra large tomato fruits, especially at the first harvest during the early winter, when prices tend to be high, were improved by growing sunn hemp as a cover crop and applying composts in consecutive years.
Soil fertility, i.e., nutrient concentrations and physical and chemical properties, was improved by repeatedly growing sunn hemp, or by applying high rates of composts as organic mulch in consecutive years. However an interaction effect either on tomato yield or on soil fertility between cover crops and organic mulch was not observed.

No. 3. Automated irrigation/fertigation system.
An automated drip irrigation/fertigation system was developed that interfaces an inexpensive solid state dielectric capacitance probe with a new irrigation controller. The electronic controller was designed to be readily adapted to existing commercial irrigation systems that use time clocks with a pressurized water supply. The cost of the components in this controller (not including shipping and labor costs) was $124.00, which includes the $60 sensor.
If the soil moisture is below a user-set threshold the scheduled irrigation event is initiated, but if the soil moisture is above this threshold, the event is bypassed and water is conserved. Multiple small irrigation events are scheduled each day.
The new device was field tested against other common automatic scheduling methods (fixed timer and variable timer based on historical evapotranspiration) on a drip irrigated plastic mulched tomato field at the Tropical Research and Education Center, Homestead, FL, and at the Plant Research and Education Unit, Citra, Marion County, FL. The soil water feedback irrigation control with this new device saved up to 74% water, while maintaining tomato yields with respect to the typical fixed irrigation schedule rates applied by commercial tomato growers during the winter season in the area.
Overall soil moisture based scheduling applied 55 to 80% less irrigation water and yielded Irrigation Water Use Efficiencies of 200% to 415% higher than time-based scheduling. Leachate volumes were 68-74% lower, a 90% reduction of leached NH4-N, a 75-89% reduction in NO3-N, and an 85% reduction in dissolved and total phosphorus loads. Comparisons with evapotranspiration based application rates for the Miami-Dade County area showed water savings up to 61%. Although similar savings (up to 79%) were obtained with switching tensiometers, these devices are difficult to maintain, requiring refilling twice per week in the coarse soils of south Florida, whereas the new soil water controller required no maintenance throughout the season. The new controller proved reliable and simple to use, although field validation at the beginning of the season of the water set point from laboratory calibration was necessary. This study showed that the combined variability of the soil and the water probes can result in relatively high variability of water application, although the resulting variability of tomato yield was less.
To further improve the system’s nutrient management, an automated fertigation system to be integrated within a soil moisture-based irrigation system was developed and tested. The system used a venture injector and provided sufficiently accurate fertilizer applications to meet crop nutrient requirements throughout the season. The system was relatively inexpensive and easy to manage.
An experiment on a plastic mulched zucchini crop was conducted to better understand the spatial soil moisture dynamics, which are critically important, since the information from the soil moisture probe drives the irrigation. Soil moisture in a narrow zone of up to 15 cm from the drip line was influenced by irrigation events in the rapidly draining sandy soil. Soil moisture tensions were found to increase rapidly beyond the 8% soil moisture by volume. Temperature and rainfall showed very little effect on output readings of the dielectric capacitance probe, but salinity effects could be significant and need to be calculated. The system proved to be successful at improving water and nutrient use efficiencies, and shows potential for facilitating improved coexistence of vegetable production adjacent to fragile natural ecosystems.
Additional information is at http://vfd.ifas.ufl.edu/gainesville/irrigation/index.html

No. 4. Influence of various crops in rotation on population of soil nematodes.
The results showed that some crops, e.g., marigolds, sunn hemp and velvetbean, effectively suppressed root-knot nematodes, but other crops, e.g., okra, Indian mustard and radish, were very susceptible to the root-knot nematode, Meloidogyne incognita (Kofoid and White) Chitwood. Furthermore, the antagonistic effects of these nematode resistant crops carried over to reduce the infestation of parasitic nematodes in the subsequent crops. The results indicate that rotating marigold with ornamental plants or cover crops with field or cash crops can substantially suppress soil parasitic nematode populations and benefit the following crops.

No. 5. Influence of cover crops in rotation on improving okra (Abelmoschus esculentus L.) yield and suppressing parasitic nematodes.
The cover crops utilized in the field and pot experiments were sunn hemp (Crotalaria juncea), cowpea (Vigna unguiculata), velvetbean (Mucuna deeringiana) and sorghum sudangrass (Sorghum bicolor × S. bicolor var. sudanense). A nematode susceptible vegetable crop, okra (Abelmoschus esculentus) was grown in rotation with these given cover crops.
The results indicated that all four cover crops improved the subsequent okra yields, and especially sunn hemp and velvetbean, which produced large amounts of biomass with high contents of nitrogen (N). The okra fruit yields in the field were increased by 33% and 11% in velvetbean and sunn hemp treatments compared that in the sorghum sudangrass treatment, which is the conventional cover crop treatment in this area.
In crop rotation studies conducted in pots, okra fruit yields were increased by 3.6, 3.1 and 1.5 times by rotation with sunn hemp, velvetbean and cowpea, respectively, compared to yields of okra following okra. Populations of root-knot nematodes were substantially suppressed by sunn hemp, cowpea and velvetbean, and this suppression was especially strong by sunn hemp. Moreover, the root knot nematode suppressive effect of sunn hemp persisted to protect a subsequent okra crop.
The results indicate that rotating the summer cover crops, sunn hemp or velvetbean, with okra can significantly improve okra yields in addition to suppressing root knot nematodes.

No. 6. Influence of cover crops and soil amendments on okra production and soil nematodes.
Among organic amendments, the application of biosolids produced the highest okra yield and biomass, and suppressed plant-parasitic nematodes in the soil the most. Sunn hemp was superior to sorghum sudangrass in improving okra production and in suppressing plant-parasitic nematodes.
There was a significant interaction between cover crops and certain organic amendments on the suppression of plant-parasitic nematodes. In particular growing sunn hemp as a green manure and applying certain organic amendments can improve okra production, and has the potential for significant application in organic farming and more broadly in sustainable agriculture.

No. 7. Summer Cover Crops and Soil Amendments to Improve Growth and Nutrient Uptake of Okra
All of the cover crops, except sorghum sudangrass in 1st year, significantly improved okra fruit yields and the total biomass production, i.e., fruit yields were enhanced by 53 – 62% in the 1st year and by 28 – 70% in the 2nd year. Soil amendments enhanced okra fruit yields from 38.3 g/pot to 81.0 g/pot vs. 27.4 g/pot in the control in 2002-03, and from 59.9 g/pot to 124.3 g/pot vs. 52.3 g/pot in the control in 2003-04.
Both cover crops and soil amendments can substantially improve nutrient uptake and distribution. Among cover crop treatments, sunn hemp showed promising improvement in concentrations of calcium (Ca), zinc (Zn), copper (Cu), iron (Fe), boron (B), and molybdenum (Mo) in fruit, magnesium (Mg), Zn, Cu, and Mo in the shoot, and Mo in the root of okra. Among soil amendments, biosolids had a significant influence on most nutrients by increasing the concentrations of Zn, Cu, Fe, and Mo in the fruit, Mg, Zn, Cu, and Mo in the shoot, and Mg, Zn, and Mo in the root.
Concentrations of the trace metal, cadmium (Cd), were not increased significantly in either okra fruit, shoot or root by application of these cover crops or soil amendments, but the lead (Pb) concentration was increased in the fruit by application of a high rate (205 g/pot) of biosolids.
These results suggest that cover crops and appropriate amounts of soil amendments can be used to improve soil fertility and okra yield without adverse environmental effects or risk of contamination of the fruit. Further field studies will be required to confirm these findings.

No. 8. Conservation of soil and nutrients by cover crops under high and low rates of simulated rainfall
To investigate the influence of summer cover crops on the retention of clay soil particles in the rhizosphere and the leaching of nutrients from the soil, a pot experiment was carried out by measuring the effects of treating legume and non-legume cover crops and somewhat weedy fallow (control) to two rates of simulated rainfall. The cover crops were sunn hemp (Crotalaria juncea L), cowpea (Vigna unguiculata L.), velvetbean (Mucuna deeringiana (Bort.) Merr.) and sorghum sudangrass (Sorghum bicolor × S. bicolor var. ‘sudanense’ (Piper) Stapf) and the two rates of water supply used to simulate leaching by rainfall were 11.6 mm week-1 (high) and 5.8 mm week-1 (low) on average, respectively.
The amounts of leachate were recorded and collected daily and the quantities of NO3-N, NH4-N and inorganic P were determined once per week. At the end of the experiment intact soil cores were collected and separated in 0-10 cm, 10-20 cm and 20-30 cm of the profile, respectively, to determine the sizes of soil particles and their redistribution in the soil profile.
The results showed that the influence of cover crops on retention in the soil of N and P depends on the crop species and on the rate of simulated rainfall applied. At the low simulated rainfall rate ( 5.8 mm week-1 on average), the concentrations of NO3-N in the leachate ranged from 0.21 to 1.89 mg l-1 with cover crops in contrast to 2.86 mg l-1 in the leachate under fallow. The corresponding average amount of NO3-N in the leachate under the low simulated rainfall rate ranged from 0.4 and 1.6 kg ha-1 equivalent under cover crops in contrast to 8.3 kg ha-1 under fallow during the three month period (Jun. to Sept.).
At the high simulated rainfall rate (11.6 mm week-1 on average), 0.39 to 2.48 mg l-1 of NO3-N was found in the leachate under the cover crops compared to 1.17 mg l-1 in the leachate under fallow. The equivalent amount of NO3-N in the leachate under the high simulated rainfall rate ranged from 2.4 to 13.7 kg ha-1 under the cover crops compared to 7.0 kg ha-1 under fallow.
The results showed that simulated rainfall at high intensity can increase the amount of N and P leached out from the soil profile, and also cause clay soil particles to leach downward in the soil profile. However, among the cover crops investigated, sunn hemp could conserve 61.4% N, and 74.4% P at the high simulated rainfall rate and 95.0% N and 87.3% P at the low simulated rainfall rate compared to the control (fallow with weeds).
Also under the simulated high rainfall rate the retention of clay contents in various layers of the soil profile was greater under sunn hemp compared to the control by 26% in the 0-10 cm layer, 20% in the 10-20 cm layer and 33% in the 20-30 cm layer of the soil profile. Therefore, sunn hemp can be considered as a promising summer cover crop for use in a tropical or subtropical region because it conserves soil and nutrients, sequesters nutrients from the previous cash crop, and produces a large quantity of biomass.

No. 9. Joint use of organic and plastic mulch to improve bell pepper production in a subtropical region (manuscript not yet been prepared).
The following comments are preliminary, since the study is still underway.
Marketable pepper yields from 5 harvests in the various treatments are shown in the following table.

Table 4. Bell pepper marketable yields (t/ha) influenced by different treatments.
All of the treatments included sorghum sudangrass (SS), which was grown on all of plots, flail-mowed and soil-incorporated. Compost was placed on some of the plots to serve as an organic mulch (OM). Some plots were covered with plastic mulch (PM).

Harvest-1 Harvest-2 Harvest-3 Harvest-4 Harvest-5 Total
————————————— t/ha ————————————-
SS + OM + PM 6.70 a* 6.26 a 6.07 a 5.57 a 6.35 a 30.95 a
SS + MC33† + PM 6.36 a 4.78 ab 4.26 ab 4.65 ab 5.01 ab 25.05 b
DM+DEV‡ + OM + PM 4.98 ab 3.52 bc 2.75 bc 4.61 ab 3.24 bc 19.10 c
DM+DEV + OM 2.22 b 2.36 c 2.72 bc 3.33 bc 2.97 bc 13.60 d
SS +PM 1.90 b 2.13 c 0.97 c 2.34 c 2.06 c 9.40 e
* Means in each column followed by same letters represent no significance at P ≤ 0.05.
† MC33: Mixture of methyl bromide (33%) and chloropicrin (67%).
‡ DM/DEV: Tank mix of Devrinol and Dual Magnum.

The yield in the organic mulch plus plastic mulch treatment was higher than in the fumigation with MC-33 plus plastic mulch treatment. A possible explanation for this result is that the organic mulch not only provides nutrients but also a sterile haven for some of the pepper roots. At the same time the plastic mulch maintains near optimal moisture and temperature.
The yield in the herbicides plus organic mulch plus plastic mulch treatment was substantially greater than in the herbicides plus organic mulch treatment; and this suggests that the plastic mulch serves to maintain more favorable moisture and temperature conditions than provided by organic mulch alone. Also it is quite remarkable that the organic mulch plus plastic mulch treatment yielded far more than the herbicides plus organic mulch plus plastic mulch treatment. The pepper plants in the latter treatment did not show overt signs of phytotoxicity, and this may suggest that the herbicides may inhibit the release of nutrients from the decaying compost. Perhaps the as yet unknown mechanism also is responsible for the huge difference in yield between the compost + plastic mulch treatment (31 t/ha) and DM+DEV + compost + plastic mulch treatment (19.1 t/ha).
From a purely technical perspective, this study suggests that soil fumigation with MC-33 is not always essential for obtaining high pepper yields, and that in many fields in south Florida this can be accomplished by growing a dense cover crop followed by the joint use of an organic mulch and a plastic mulch. Probably the key question is whether this system would be sufficient in fields heavily infested with nutsedges.

Figure 1. Influence of treatments on root gall scale (0-5) of bell pepper. 0: without a root gall, 1: < 20%, 2: 20-40%, 3: 40-60%, 4: 60-80%, and 5: 80-100% of roots with galls. DM/DEV: Devrinol + Dual Magnum, CO: compost applied as an organic mulch, PM: plastic mulch, MC33: methyl bromide (33%) plus chloropicrin (67%). Vertical bars in the chart each represent standard deviation of the mean of 4 replicates.
Figure 2. Status of pepper plantings at the Tropical Research & Education Center, Hometead, FL at blooming: 1. Sorghum sudangrass (SS) + plastic mulch (PM), 2. Sorghum sudangrass (SS) + Dual Magnum (DM) & Devrinol (DEV) + organic mulch (OM) of compost + plastic mulch (PM), 3. Sorghum sudangrass (SS) + organic mulch (OM) of compost + plastic mulch (PM), 4. Sorghum sudangrass (SS) + Dual Magnum (DM) & Devrinol (DEV) + organic mulch (OM) of compost, and 5. Sorghum sudangrass (SS) + MC-33 fumigant + plastic mulch (PM).
Note: The sizes of the pepper plants varied in the following increasing order:
[SS+PM]< [SS+MC-33] < [SS+DM+DEV+OM] < [SS+DM+DEV+OM+PM] < [SS+OM+PM]. No. 10. Using high-residue cover crop mulch for weed management in organic no-till potato production systems. Virginia Component. A unique organic raised-bed (185-cm wide) zone production system was studied at Virginia Tech. For example, on 20 July 2004, bed tops (75-cm wide) were drill-seeded with three different summer cover crops: sunn hemp (SH), lablab (LL) and bell bean (BB), compared to a control, no cover crop (NC). Alleyways (bed shoulders and bottoms, 110-cm wide) were seeded with sorghum sudangrass (SSG) in all plots except the control. On 26 April 05, potato seed pieces were no-till planted in twin rows (50-cm apart) and grown without using chemical fertilizers or pesticides.
Weed suppression was best in plot areas covered with SSG, SH and LL residues; weed suppression was particularly poor in no-cover plots. Tuber yields were excellent in all treatments, averaging 25.4 t/ha; however, yield was 14% higher in SH and LL plots than in BB and NC.
Weed management is considered the most challenging production problem facing organic farmers. Without effective herbicides, organic growers normally rely on hand weeding and multiple cultivations, which can be expensive, time consuming and degrade soil quality. Applying thick layers of organic mulch can control weeds; however, this practice is normally cost-prohibitive. Although equally challenging, organic no-tillage (NT) systems offer cost-effective improvements in both weed management and soil quality.
This study demonstrates that high-residue raised-bed NT systems are a viable option for producing organic potatoes, particularly in warm long-season climates. Success is most likely achieved in climates and situations where high-residue mulch favorably impacts the growing environment of the potato crop—e.g. suppression of weeds and pests (e.g. Colorado potato beetle), moderation of soil temperature, increased plant-available water and nutrients, and improved soil quality. Recommended best-management practices arising from these studies include (1) erecting and nutrient loading (soil building) raised beds before seeding cover crops; (2) drilling high-residue grass-legume mixtures on raised beds–e.g. rye/hairy vetch and barley/hairy vetch; (3) achieving high soil tilth in in-row areas (grow zones) by using potato planters equipped with a wide-wing subsoil shank; and (4) post-plant killing cover crops (2-3 wk after planting potato seed pieces). Suggestions are also given for using strip-till methods in field and climatic situations not suitable for high-residue NT systems.

Table 5. Effects of tillage/cover treatments on biomass of cover crops and weeds and marketable potato tuber yield, 2002-2004.

Biomass (lb dry wt/acre) Marketable tuber yieldz
Tillage/cover crop Cover Crops Weeds Cwt/acre Rel. yield (%)
2002____________________
Conventional-till (CT) —– 81 124ab 100
No-till (NT)–rye 6,050 57 116b 94
NT–rye/hairy vetch 5,630 158 138a 113
NT—rye/crimson clover 6,240 205 111b 90
Significance —– —– * —–
2003____________________
Conventional-till (CT) —– 903 146 100
NT—rye 6,880 1,420 121 83
NT—rye/hairy vetch 6,550 1,060 141 97
Significance —– —– NS —–
2004___________________
Conventional-till (CT) —– 960 167b 100
NT—oats/rye/hairy vetch 6,550 71 208a 125
NT—barley/hairy vetch 8,580 107 216a 129
NT—oats/hairy vetch/Aust. pea 4,410 178 192ab 115
Significance —– —– * —–
zRelative yield, compared to the control, CT plots (100); cwt = hundred weight (100 lb).
NS, *Nonsignificant and significant at P = 0.05. Mean separation by Fisher’s LSD test.

Figure 3. Uniform high-density rye-legume cover crop in early April, suppressing winter weeds and resulting in uniform high-residue mulch in May.

Figure 4. Twin-row arrangement on NT rye raised-bed system (4-5 wk after planting); note uniform dense mulch still remaining over the entire bed.
Tuber yield. Yield of marketable creamer (2002) and table-stock (2003-2004) potatoes was equal or higher in NT rye/hairy vetch and NT barley/hairy vetch plots than in NT rye or CT plots (Table 5). In 2002, similar yield responses in NT rye and NT rye/crimson clover plots probably occurred because the proportion of crimson clover was very low (<5%) in the rye/crimson clover plots. Final potato germination was high every year, averaging 89%. Although first-emerged plants were mainly in CT plots (at 3 wk after planting, WAP), final counts at 5 WAP were not affected by treatment (data not shown).
In 2004, organic tuber yields in NT plots were similar to the state average for non-organic commercially grown CT potatoes (Anonymous, 2004). Potato yields in 2003 were approximately 35% lower than in 2004 (Table 5). Near record rainfall occurred in 2003, accompanied by abnormal cloudy weather, compared to more normal conditions in 2004. These weather differences probably contributed heavily to yield differences between years. The soil was unusually compacted in 2003, possibly caused by pounding heavy rainfall and reduced microbial activity arising from excessive soil moisture throughout much of the growing season.
Since hilling is not used in raised-bed systems, achieving proper soil tilth and aeration in the potato grow zones is a major determinant for success in organic NT systems (Morse, 1997; Mundy et al., 1999). To ensure proper tilth and aeration in grow zones at planting, the SST-T was equipped with an aggressive 6-inch wide winged subsoil shank that loosened in-row bed areas (grow zones). In 2003, however, the SST-T was equipped with a less aggressive soil loosening system, which possibly contributed to the compacted beds and reduced marketable tuber yields.

Weed suppression. Overall, weed growth in this 3-year study was held below yield-limiting levels without applying herbicides, indicating that the cover crop production and management system employed in these experiments can be used to produce organic potatoes. Cover crop biomass was thick and evenly distributed over the entire bed surface in all NT plots in these experiments. Generally, mature high C:N cereal grain residues persist longer and suppress weeds better than low C:N legumes (Morse, 1999). Although the proportion of cereal grains (rye and barley) was considerably higher in 2002 and 2003 than 2004 (data not shown), weed suppression did not correlate strongly with cover crop types. Weed biomass, however, was correlated with seasonal rainfall. Highest weed biomass levels occurred in 2003, which had near record seasonal rainfall. Much of the weed biomass in NT plots in 2003 was cover crop regrowth. Enhanced weed growth in wet years is a predictable response, especially in organic systems, where herbicides are prohibited (Barker and Bhowmik, 2001). Infante and Morse (1996) showed that weed biomass levels exceeding 1,000 lb/acre at canopy closure were needed to reduce broccoli yield. Weed biomass was at or above this critical level in 2003 and the CT plots in 2004 and possibly explain the reduced potato yields associated with these plots.
When attempting to adopt NT systems, a major challenge is to accurately predict the weed suppression potential of any given situation. Six criteria for assessing the probability of achieving weed suppression in organic NT systems are presented in Table 6 (Morse and Creamer, 2005). Weed suppression is likely when most or all the six factors are in the medium to high probability categories (Table 6). Using the six factors listed in Table 6 as a guide helps explain why weed suppression was high in these experiments. Mulch quantity and quality were in the medium-high categories. Delayed killing cover crops until near potato sprout emergence and planting high-density twin rows favored rapid canopy closure (4-5 wk from emergence). All applied organic fertilizer and irrigation water were precision placed in the potato grow zones, favoring growth of potatoes over weed growth.
In 2002, subplots were sprayed with recommended herbicides (S-metolachlor and linuron) to assess effectiveness of the high-residue mulches to suppress weed growth. Both weed biomass and potato tuber yield were unaffected by herbicide applications, indicating that the high-residue mulch system used held weeds below yield-limiting levels (data not shown).

Insect management. High-residue cereal grain straw mulch is known to greatly reduce potato yield losses caused by Colorado potato beetle (CPB) (Wyman et al., 1994). Although CPBs were present at KARF all three years in non-organic vegetable and potato fields, incidence of CPB in organic plots was very low (data not shown). Low incidence of CPBs in these studies is attributed to persistent high-residue mulch in the NT plots and associated farmscape plantings (Wyman et al., 1994).

Table 6. Criteria for assessing probability of weed suppression in organic no-till systems (Morse
and Creamer, 2005).

Site factor Probability of achieving weed suppression
(criterion)z Low Moderate High
Mulch quantityy—dry wt (ton/acre) <2 2-4 >4
—soil coverage (%) <75 75-95 >95
—depth (inch) <2 2-4 >4
Mulch quality—C/N ratio <15 15-25 >25
Perennial weeds (% of total weeds) >20 2-20 <2
MWFP (canopy closure, wk) >6 4-6 <4
Monthly in-season rainfall (inch) >4 2-4 <2
Fertigation method overhead furrow drip

zC/N ratio = carbon to nitrogen ratio (wt to wt basis); MWFP = minimum weed-free period, defined as the length of time a crop must remain free of weeds after planting in order to prevent yield loss—normally, the MWFP coincides with the time of canopy closure; fertigation = when water and soluble organic fertilizer are applied in the irrigation system.

yJohn Teasdale, personal communication.

This research has assessed the capacity of high-residue NT systems to suppress weeds and achieve profitable marketable yield of organic potatoes. Success with organic NT potato systems is most likely to occur in fields where high-residue surface mulch favorably impacts the growing environment of the potato crop—e.g. suppresses weeds and pests, enhances availability of water and nutrients, moderates soil temperature, and improves soil quality. Based on these research data, related experiments and grower experiences, several recommendations are presented.
Recommendation No. 1. Grow potatoes on raised beds. Erecting preformed raised beds in late summer before drilling cover crops can be of critical importance, especially in fine-textured soils and cooler short-season climates. Erecting and maintaining wide beds (5-7 ft center-to-center, 3-5 ft on bed tops, and 7-9 inches high) and using high-density plantings (2-3 rows per bed) constitute a permanent controlled-traffic system that can achieve rapid canopy closure and improve weed suppression on bed tops (Magdoff and van Es, 2000).
Judicious use of crop rotations on permanent wide raised beds can enhance both short- and long-term soil tilth and plant-available nutrients and water, especially if organic-approved soil amendments (compost, manure, lime, gypsum) are thoroughly mixed deep in the soil profile during bed establishment. After harvesting, the location and integrity of beds can be maintained by using zone tillage implements (rototillers, spading machines, powered harrows) and ridging (bed-making) equipment to rebuild the beds and incorporate crop and weed refuse and applied soil amendments. Bed rebuilding and drilling cover crops immediately after harvest can prevent or minimize weed seed production, soil erosion and leaching of nutrients, and enhance long-term weed suppression and soil quality (Morse and Creamer, 2005)
.
Recommendation No. 2. Produce in-situ high-residue cover crops. High-residue mulch—either produced in-situ and/or applied—can increase potato tuber yields, especially in warm climates and under moisture-deficit conditions (Midmore, 1991). Weeds can be held below yield-limiting levels in organic NT systems, provided that requisite (1) production and management of high-residue cover crops and (2) stand establishment and vigorous crop growth are achieved. Diverse crop rotations involving different cover crops and cash crops are highly recommended for all productions systems—chemical-based, organic, and integrated.
Use of high-residue cover crop mulch is considered essential for weed suppression in organic NT systems, particularly for inter-bed areas (alleyways). Uniform high-density cover crop stands are achieved more readily by seeding with precision drills than broadcasting and mechanical seed incorporation. Properly adjusted precision drills are particularly effective for achieving uniform dense stands on raised beds. Generally, grass cover crops or grass-legume mixtures suppress weeds better and persist as dead mulch longer after being killed than legume monocultures.
Strip intercropping high-residue weed-suppressing cover crops such as cereal rye in alleyways and growth-promoting cover crops on bed tops offer great potential for future research (Chen et al., 2004; Morse and Schonbeck, unpublished data, 2004; Tanaka et al., 2005). Examples of growth-promoting cover crops are (1) legume monocultures or legume-grass mixtures (e.g. rye/hairy vetch or barley/hairy vetch) for enhancing plant-available nitrogen, and (2) tropical winter-killed species (e.g. sunn hemp and/or sorghum sudangrass), brassica monocultures (e.g. oilseed radish), or brassica-legume mixtures (e.g. oilseed radish and crimson clover) for improved nitrogen fertility, pest suppression, and vertical zone building.

Recommendation No. 3. Manage cover crops to maximize weed suppression. To be an effective weed management tool, cover crops must (1) produce high biomass levels (3 or more tons/acre) (2) be easily killed by mechanical methods, (3) suppress weed-seed germination and/or weed growth for a sufficient duration to minimize weed-crop competition, and (4) not interfere directly with crop growth—i.e. must not be allelopathic to crop growth. Many factors interact to determine the capacity of cover crops to suppress weeds below crop yield-limiting levels (Table 6).
For potatoes, proper coordination (timing) of crop establishment (planting date) and killing date of cover crops can play a major role in achieving weed management and tuber yield. High-residue living cover crops suppress weeds better than dead mulch; thus, delayed killing cover crops until just before potato sprout emergence (2-3 wk after planting) will improve weed suppression on bed tops, especially in twin-row high-density potato plantings. To effectively suppress weeds, dead cover crop mulch must be spread uniformly over the soil surface. Thus, use roller-crimpers or flail mowers to kill mature cover crops and avoid using implements such as rotary mowers that windrow residues (Creamer and Dabney, 2002). In Times of excessive early-season rainfall, remedial weed management measures (hand weeding, cultivation, acetic acid sprays) may be required to minimize weed-crop competition and crop yield losses (Al-Khatib, 1994; Barker and Bhowmik, 2001; Morse and Creamer, 2005). In all cases, roguing to prevent production of weed seeds is an important cultural practice for organic growers, and is considered essential for organic farmers who are exploring NT systems for production of potatoes or any other crop. Roguing out escape weeds by hand or using high-residue cultivators can prevent weed seed production.

Recommendation No. 4. Use properly equipped planters to establish potato seed pieces in untilled mulched beds. For best results, NT planters should be equipped to slice surface residues, till in-row strips (grow zones), precision place potato seed pieces 5-6 inches deep in the grow zones, and precision place organic fertilizer and drip tubing, if needed. Planting must be accomplished with minimum disturbance of surface residues and surface soil. To improve weed management, plant twin rows (18-24 inches apart and 9-12 inches in-row), mix fertilizer in the grow zones, delay killing cover crops until just before sprouts emerge, irrigate as needed, and apply extra mulch 1-2 wk after sprout emergence, if needed.

Literature cited
Al-Khatib, K. 1994. Weed control with green manure and cover crops. Final Report—Organic Farming Research Foundation, Santa Cruz, CA.
Anonymous. 2004. Virginia Agriculture Statistics Bulletin and Resource Directory, Virginia Agricultural Statistics Service, Richmond, VA.
Barker, A.V. and P.C. Bhowmik. 2001. Weed control with residues in vegetable cropping systems. J. Crop Production 4:163-183.
Chen, C. M. Westcott, K. Neill, D. Wichman, and M. Knox. 2004. Row configuration and nitrogen application for barley-pea intercropping in Montana. Agron. Journal 96:1730-1738.
Creamer, N.G. and S.M. Dabney. 2002. Killing cover crops mechanically: Review of recent literature and assessment of results. Alternative Agriculture 17:32-40.
Infante, M.L. and R.D. Morse. 1996. Integration of no-tillage and overseeding legume living mulches for transplanted broccoli production. HortScience 31:376-379.
Magdoff, F. and H. van Es. 2000. Building soils for better crops, p. 125133. Sustainable Agriculture Network, Burlington, VT.
Midmore, D.J. 1991. Potato production in the tropics, p. 728-793. In The Potato Crop, Second Edition. Chapman and Hall, London.
Morse, R.D. 1997. No-till production of Irish potato on raised beds, p. 117-121. In R.N. Gallaher and R. McSorley (eds.) Proc. Southern Conservation Tillage Conference for Sustainable Agriculture, Gainesville, FL.
Morse, R.D. 1999. No-till vegetable production—its time is now. HortTechnology 9:373-379.
Morse, R.D. and N.G. Creamer. 2005. Developing no-tillage without chemicals: The best of both worlds? In A. Taji and P. Kristiansen (eds.) Organic Agriculture: A Global Perspective. CSIRO Publishing, Collingwood, Australia (in press).
Mundy, C. N.G. Creamer, C.R. Crozier, L.G. Wilson, and R.D. Morse. 1999. Soil physical properties and potato yield in no-till, subsurface-till, and conventional-till systems. HortTechnology 9(2):240-247.
Tanaka, D.L., R.L. Anderson and S.C. Rao. 2005. Crop sequencing to improve use of precipitation and synergize crop growth. Agron. Journal 97:238-240.
Wyman, J.A., J. Feldman and S. K. King. 1994. Cultural control of Colorado potato beetle: Off-crop management, p. 376-385. In G. N. Zehnder, M.L. Powelson, R.K. Jansson, and K.V. Raman (eds) Advances in potato pest biology and management. APS Press. St. Paul, MN.

Participation Summary

Educational & Outreach Activities

Participation Summary

Education/outreach description:

1. Abdul-Baki, A. A.,W. Klassen, H. H. Bryan, M. Codallo, B. Hima, Q. R. Wang, Y. Li, Y.-C. Lu, and Z. Handoo. 2005. A Biologically-Based System for Winter Production of Fresh-Market Tomatoes in South Florida. Proc. Fla. State Hort. Soc. 118: 153-159.
2. Dukes, M. D., R. Muñoz-Carpena, and L.W. Miller. Quantified Soil Moisture-Based Irrigation Control System. UF#11415. US Patent Applied in 2004.
3. Morse. R. 2007. Using high-residue cover crop mulch for weed management in organic no-till potato production systems. Organic Farming Research Foundation. 16 pages.
4. Munoz-Carpena, R.. 2004. Field devices for monitoring soil water content. ABE 343. Http://edis.ifas.ufl.edu
5. Munoz-Carpena, R., J. Schroder, M. Dukes, Y. Li and W. Klassen. 2007. Fertigation methods for soil-moisture-based irrigation of field-grown tomatoes on coarse soils in Florida. EDIS. (In preparation.)
6. Munoz-Carpena, R., J. Schroder, M. Dukes, Y. Li and W. Klassen. 2007. Low cost injection system combined with soil moisture-based irrigation for precision fertigation of vegetable crops. EDIS. (In preparation)
7. Munoz-Carpena, R., J. Schroder, M. Dukes, Y. Li and W. Klassen. 2007. Selecting and calibrating Venturi injectors for fertigation of vegetable crops. EDIS. (In preparation.)
8. Munoz-Carpena, R., M. D. Dukes, Y. Li and W. Klassen. 2005. Field Comparison of Tensiometer and Granular Matrix Sensor Automatic Drip Irrigation on Tomato. HortTechnology 15 (3): 584 – 590.
9. Munoz-Carpena, R., J. Schroder, M. Dukes, Y. Li and W. Klassen. 2006a. Low cost injection system combined with soil-moisture-based irrigation for precision fertigation of vegetable crops. EDIS
10. Munoz-Carpena, R., J. Schroder, M. Dukes, Y. Li and W. Klassen. 2006b. Selecting and calibrating Venturi injectors for fertigation of vegetable crops. EDIS
11. Munoz-Carpena, R., J. Schroder, M. Dukes, Y. Li and W. Klassen. 2006c. Fertigation methods for soil moisture-based irrigation of field-grown tomatoes on coarse soils in Florida. EDIS
12. Munoz-Carpena, R. and M.D. Dukes. 2005. Design and field evaluation of a new controller for soil moisture-based irrigation. Submitted to Applied Engineering in Agriculture (Manuscript no. SW-06008-2005, August 2005).
13. Munoz-Carpena, R. and M. D. Dukes. 2005. Automatic irrigation based on soil moisture for vegetable crops. ABE 356. Http://edis.ifas.ufl.edu
14. Schroder, J. H. 2006. Soil moisture-based drip irrigation for efficient use of water and nutrients and sustainability of vegetables cropped on coarse soils. A thesis presented to the Graduate School of the University of Florida in partial fulfillment of the requirements for the degree of Master of Engineering. 117 pages.
15. Wang, Q., Li, Y., and Klassen, W. 2006. Summer Cover Crops and Soil Amendments to Improve Growth and Nutrient Uptake of Okra (Abelmoschus esculentus L.). HortTechnology. 16 (2): 328-338.
16. Wang, Q., W. Klassen, Y. Li, Z. Handoo, T. Olczyk and M. Codallo. 2005. Influence of Cover Crops in Rotation on Improving Okra (Abelmoschus esculentus L.) Yield and Suppression of Parasitic Nematodes. Proc. Fla. State Hort. Soc. 118: 177-183.
17. Wang, Q., Li, Y., Klassen, W., and Handoo, Z. 2007. Influence of cover crops and soil organic amendments on okra (Abelmoschus esculentus L.) production and soil nematodes. Renewable Agriculture and Food Systems. 22(1): 41-53.
18. Wang, Q. R., W. Klassen, Y. Li, and M. Codallo. 2007. Summer cover crops and organic mulch to improve tomato yields and soil fertility in a subtropical region. Agronomy Journal (submitted).
19. Wang, Q., Li, Y., Handoo, Z., and Klassen, W. Influence of cover crops in rotation on populations of soil nematodes. Nematropica. 2006 (submitted).
20. Wang, Q., Y. Li and W. Klassen. 2007. Conservation of soil and nutrients by cover crops under high and low rates of simulated rainfall. Journal of Soil and Water Conservation. (Submitted.)
21. Wang, Q., W. Klassen, Z. Handoo, A. Palmateer, and M. Codallo. 2007. Joint use of organic and plastic mulch to improve bell pepper production in a subtropical region. (Manuscript is partially prepared; data are still being collected.)
OUTREACH –DEMONSTRATIONS/EXPERIMENTS

Demonstration/Experiment in Collaboration with Strano Farms 2003-2004.
Objective: Determine relative effects of different cover crops on crop yields.
Cash crop: Zucchini squash. Note: we had planned to conduct this study with a large round tomato cultivar, but the grower decided to plant zucchini squash.
Cover crop treatments: Sun hemp, velvetbean, sorghum sudangrass and fallow.
Plot size 60 feet long and 36 feet wide, i.e., segment of 6 beds with bed centers 6-feet apart; 4 replicates; 4X4X = 16 plots. Area = 34,560 sq. ft. = 0.7934 acre.
We did not develop a report on this demonstration/study.

Demonstration/Experiment in Collaboration with La Rocca Farms 2003-2004
Objectives: (1) Determine relative effects of different cover crops on grape tomato yields.
(2) Determine effects of two different irrigation rates on grape tomato yields.
(3) Determine the effects of various fumigants on grape tomato yields.
Cash crop: grape tomato.
Cover crop treatments: Sun hemp, velvetbean, sorghum sudangrass and fallow.
Fumigant treatments: MC-33, methyl iodide-chloropicrin and KPAM.
Irrigation rates: (1) Grower rate; (2) low rate.
Plot size: 6 ft. X 73 ft.; 80 plots; 0.8044 acre.
1. All produce harvested was returned to La Rocca Farms.
2. TREC seeded the cover crops and terminated them as agreed with La Rocca Farms.
3. TREC made the beds, fumigated certain plots; La Rocca Farms planted the grape tomatoes, handled all fertilizer and pesticide applications.
4. TREC monitored soil moisture, and took responsibility for the low irrigation rate.
5. TREC attempted to work with La Rocca Farms’ contractor in taking yields, but the contract laborers could not be supervised adequately. Since the yield data are unreliable, we did not develop a report on this demonstration study.

Demonstration/Experiment in Collaboration with F&T Farms 2004-2005.
Objectives: (1) Determine relative effects of different cover crops on crop yields.
(2) Determine effects of two different irrigation rates on pepper and grape tomato yields.
Cash crop: Pepper
Cover crops: Sun hemp, velvetbean, sorghum sudangrass and fallow.
Irrigation rates: (1) Use grower’s rate as high rate, and (2) use a somewhat lower rate.
Plot size 40 feet long. Bed centers are 6-feet apart; 4 replicates; 4X4X2 =32 plots; Area required = 7680 square feet = about 0.2 acre.
Cash crop: Grape tomato
Cover crops: Sunn hemp, sorghum sudangrass and cowpea.
Irrigation rates: (1) Use grower’s rate as high rate, and (2) use a somewhat lower rate.
Plot size 40 feet long. Bed centers are 6-feet apart; 4 replicates; 3X4X2 = 24 plots; Area = 5760 square feet = about 0.2 acre.

1. All produce harvested was returned to F&T Farms.
2. TREC seeded the cover crops and terminated them as agreed with F&T Farms. S&T Farms irrigated the cover crops with a water canon during prolonged dry weather.
3. S&T Farms made the beds, planted the peppers and grape tomatoes, handled all fertilizer and pesticide applications.
4. TREC monitored soil moisture, and took responsibility for the low irrigation rate.
5. TREC attempted to work with S&T Farms’ contractor in taking yields, but the contract laborers could not be supervised adequately. Since the yield data are unreliable, we did not develop a report on this demonstration study.

Group Learning Events on Sustainable Cultural Practices, Nutrient Management and Cover Crops organized and led by Teresa Olczyk.

2006. Water Quality Sampling and Monitoring Technology In-Service Training (18 participants).
Vegetable Gardening Class. 2006. (45 participants).
2005. South Florida Vegetable Irrigation and Nutrient School (55 participants).
2005. Vegetable Field Day at TREC- Automated Irrigation and Fertigation. (28 participants).
2004. South Florida Vegetable Irrigation and Nutrient School. (80 participants)
2004. How to Use Tensiometers for Scheduling Irrigation. Sweet Corn Field Day. (18 participants).
2004. Agriculture, Restoration and Hydrology, Water Quality and Flow in the Frog Pond Area. (16 participants).
2004. New Soil and Water Management Practices Workshop. (15 participants).
2004. Vegetable and Agronomic Crop Best Management Practices Workshop (organized in cooperation with the Florida Department of Agriculture and Consumer Services Office of Agricultural Water Policy to discuss draft of the BMP Manual for Agronomic and Row crops. (35 participants).
2004. Best Management Practices Discussion Workshop. (32 participants).
2003. The Second South Florida Drip Irrigation School. (78 participants).
2002-2004. Co-organized and conducted four seminars related to hydrology and water use research and the C-111 project (in cooperation with extension specialists at UF IFAS TREC) for international visitors. (65 participants).

Research Trials and Extension Field Demonstrations involving Ms. T. Olczyk:

2003. A one acre field demonstration of the performance of drip tapes in calcareous soils was established by the agent at the UF IFAS TREC. Blue dye was injected to demonstrate wetting patterns for different drip tapes. Five tomato growers (representing 80% of tomato acreage in Miami-Dade County) were able to evaluate wetting patterns for different irrigation drip tapes.

2003-2006. T. Olczyk, with the help of R. Regalado, an extension biologist, participated in seven TREC field studies, as a cooperator on research grants, which demonstrated irrigation scheduling for tomato, grape tomato and pepper. She also coordinated testing and installation of tensiometers and collecting and interpreting the soil moisture data.

2003-2004. Cooperated with Dr. R. Munoz-Carpena, Hydrologist, and Dr. Yuncong Li, Soil Specialist from UF IFAS TREC on laboratory and field performance evaluations of several new water status monitoring devices for calcareous soils in Miami-Dade County. Results of this study were presented to the growers during workshops.

As requested by the area growers and the Miami-Dade County Vegetable Advisory Committee, the following field demonstrations were conducted in growers’ fields. Some of these trials were established in cooperation with the state extension specialists and other researchers as components of grants. Seed company representatives also cooperated. Ms. Olczyk secured cooperation from farmers for on-farm projects, planted or participated in establishing of the demonstration sites, participated in collecting and evaluating data and organized educational programs (field days and workshops) for growers. The on-farm trials and extension demonstrations are important tools in teaching producers about sustainable farming practices.

Two demonstrations of cover crop influence on a root knot nematode population for okra and summer squash, (2003-2005).

Four field trials evaluating cover crops as biological and chemical alternatives for Methyl Bromide for tomato and bell pepper production. (2003-2005).

Cover crops/ irrigation and soil amendments as possible alternatives to Methyl Bromide for eggplants, pepper and grape tomato production. (2004-2005).

Tensiometer Service for Growers: 2003-2007. Ms. T. Olczyk and County Extension biologist, R. Regalado, have provided cleaning, repair service, calibration with the vacuum calibration chamber, and installation of tensiometers for vegetable, fruit and ornamental growers. Growers interested in testing tensiometers before purchasing them are trained in the use of this equipment and can borrow instruments from the agent for four weeks to become familiar with the use and interpretation of readings for scheduling irrigation. The agent cooperates with USDA NRCS specialists in this program.

Water Use Conservation Survey: 2003-2005. Ms. T. Olczyk cooperated with Dr. R. Munoz-Carpena, the hydrologist from UF IFAS TREC, and other Agriculture and Horticulture extension agents dealing with agricultural water use on developing and conducting a “Water Conservation Survey” for vegetable farmers, ornamental nurseries and golf courses in Miami-Dade County. A questionnaire was sent to about 600 ornamental nurseries, tropical fruit growers, vegetable growers and the golf course managers. The survey contained questions about water management and conservation practices, knowledge and competencies concerning irrigation practices and environmental attitudes.
The results from 167 respondents were tabulated and presented at grower meetings and scientific conferences. Results of this survey are being used to develop research and extension educational programs that address the needs of commercial agricultural producers and golf course managers.

Project Outcomes

Project outcomes:

1. A biologically based tomato production system was found to result in higher economic returns per acre than the commercial standard system based on soil fumigation with methyl bromide and chloropicrin. This result has not been given much positive attention, and the industry is still intent on seeking annual renewals of a critical use exemption for methyl bromide in the production of tomato, pepper, eggplant and strawberry. However it seems likely that after the methyl bromide era has come to an end that many growers will be inclined to accept biologically-based approaches.
2. In study No. 2 summer cover crops used as green manures and compost used as an organic mulch in several consecutive years were found to improve tomato yields and soil fertility. The main challenge in using such a production system is the control of weeds. However in study No. 9 we found that by (a)growing a dense cover crop, which suppresses weeds, (b) next applying a thick organic mulch, and (c) then applying a plastic mulch, that the yields of pepper were significantly higher than in the fumigation with MC-33 plus plastic mulch treatment. A possible explanation for this result is that the organic mulch not only provides ample nutrients but also a sterile haven for some of the pepper seedling’s roots. At the same time the plastic mulch maintains near optimal moisture and temperature. Since we are seeing this same result in the 3rd consecutive year, we have planned a field day. We feel confident that at least the organic growers will adopt this system.
3. An automated drip irrigation/fertigation system was developed that interfaces an inexpensive solid state dielectric capacitance probe with a new quantified irrigation controller. This system provides multiple small low-volume irrigation events each day, and thereby eliminates leaching of nutrients, while optimally meeting the needs of the crop. It seems likely that most of this system will be adopted widely as pressures mount to implement Best Management Practices and as water becomes more expensive. All users of water in south Florida were required to pay for it for the first time in 2007. Thus an incentive has been created to use water sparingly, and if this is achieved through precision irrigation/fertigation, the impact of agriculture on natural ecosystems will be greatly reduced. However calibration of the probe is still too challenging for the average layperson, and this needs to be resolved. Nevertheless the system can be operated with inputs from tensiometers, which require frequent servicing.
4. Studies No. 4, 5 and 6 demonstrated that the plant parasitic nematode-suppressive effects of certain summer cover crops carry over to reduce infestations of parasitic nematodes in the subsequent crops. Therefore such cover crops should be recommended as essential components of crop production systems. Sunn hemp and velvetbean are among the most effective nematode-antagonistic legumes, while sorghum sudangrass is amongst the most effective nematode-antagonistic grass crops. Even though sunn hemp seed can be purchased cheaply and readily in certain tropical countries, it availability in the US has been problematic, and absolutely none was available in 2005 and most of 2006. If a sunn hemp seed becomes reliably available in future years, it is likely that substantial use will be made of this excellent cover crop. Growers have tended to avoid the use of velvetbean because the long vines often clog machinery. However, new vineless cultivars, such as ‘Georgia Bush”, can be expected to gain acceptance. Sorghum sudangrass has been widely accepted in Florida, but much of the land used for vegetable crop production is available to growers only on the basis of one-year leases, and on such land no cover crops are planted. Possibly this situation will be remedied as pressure mounts to implement Best Management practices.
5. Study No. 7 showed quantitatively that leguminous cover crops can provide a copious supply of an array of nutrients to the following cash crop, and this is also the case with a number of organic soil amendments. These materials can boost crop yields quite substantially, as has also been shown in study No. 9. The data provide a compelling case for the joint use of cover crops, organic mulches together with plastic mulch to provide an optimum environment (nutrients, moisture, temperature) in the root zone of seedlings during the critically important early phase of their growth.
6. Study No. 8 showed that by growing cover crops such as sunn hemp, the amounts of nitrogen and phosphorus leached from the root zone during simulated high rainfall events could be reduced by 61% and 74%, respectively. Thus if cover crops are grown during the fallow period, and the automated high frequency/low volume drip irrigation/fertigation system is used during crop production, the amount of nutrients leached would be very small and largely non-threatening to fragile natural ecosystems.
7. Study No. 10 demonstrated that high-residue raised-bed no-tillage systems are a viable option for producing organic potatoes, particularly in warm long-season climates. Success is most likely achieved in climates and situations where high-residue mulch favorably impacts the growing environment of the potato crop—e.g. suppression of weeds and pests (e.g. Colorado potato beetle), moderation of soil temperature, increased plant-available water and nutrients, and improved soil quality. Recommended best-management practices arising from these studies include (1) erecting and nutrient loading (soil building) raised beds before seeding cover crops; (2) drilling high-residue grass-legume mixtures on raised beds–e.g., rye/hairy vetch and barley/hairy vetch; (3) achieving high soil tilth in in-row areas (grow zones) by using a potato planter equipped with a wide-wing subsoil shank; and (4) post-plant killing of cover crops 2-3 wks after planting potato seed pieces. Suggestions are also given for using strip-till methods in field and climatic situations not suitable for high-residue no-tillage systems. We are confident that this high-residue raised-bed no-tillage system will be adopted to a significant extent by potato producers.

Economic Analysis

Biologically-based tomato production system.
For Florida tomato growers to be sustainable, they must adopt production systems that are profitable. We compared net returns, defined as the difference between gross returns and total cost, between the MC-33 treatments and the alternative cover crop systems. We created a budget for the tomato systems studied here by modifying a recent budget for the MC-33 system published by Smith (2000). Preharvest production costs included fertilizer, chemicals, seed, labor, equipment use (operation, maintenance, fuel, and depreciation), other materials (including plastic mulch and string), and land rental. One notable preharvest cost was the fumigant in the MC-33 system. In 2001/02 and 2002/03, this cost $1195/ha, and in 2003/04 the price had more-than-doubled to $2631/ha. In the cover crop systems there were additional costs for seeds, seeding, and mowing. All other preharvest costs were the same for all treatments. Labor for picking, hauling, and packing in all systems was accounted for with the costs for harvesting and marketing, which also included containers, use of hauling and packing equipment, sales and organizational fees.
Annual input costs were adjusted by the USDA-National Agricultural Statistics Service’s agricultural input price index (http://www.usda.gov/nass/graphics/data/paid.txt). Weekly Miami Terminal market prices for tomatoes were obtained from the USDA’s Agricultural Marketing Service (http://www.ams.usda.gov/fv/mnprice.htm), and averaged over the harvest season. In 2001/02 and 2002/03, prices for 25-lb cartons of extra-large and large “vine ripes” were $9.00 and $8.00, respectively. In 2003/04, prices for extra-large, large, and medium size vine ripes were $11.50, $10.50, and $10.00, respectively.
Annual costs and returns for each system appear in Table 6 of Publication No.1. In all years, every treatment produced positive net returns. In 2001/02, the range of net returns was from $17275/ha down to $12030/ha, while in 2002/03, the range was from $7930/ha down to $3495/ha. In 2003/04, the range was considerably higher, from $47820/ha down to $$28860/ha. In 2002 and 2004, extra-large fruits were responsible for the majority of revenue.
Yield and market price determined the magnitude of returns. Net returns in 2002/03 were much lower than in 2001/02, due in part to greatly reduced yield of large size tomatoes, even though yield of extra-large sized fruit did not change drastically and market prices were the same. In 2003/04, market prices had increased 22% from 2002/03 for extra-large tomatoes and 31% for large fruit. Coupled with a substantially increased yield in both of those size categories and the additional harvest of medium sized fruit, net returns in 2003/04 were by far the greatest of the three study years.

Table 7. Economic summary of tomato production under alternative cover crop systems, in years 2001/02, 2002/03, 2003/04 (in $/ha, rounded to the nearest $10).
2001 2002 2004
MC-33 Cowpea Velvet
bean MC-33 Cowpea Velvet
bean Sunn
hemp SS/MC-33 Fallow Velvet
bean Sunn
hemp
Gross returns*
size XL 25580 22730 24710 22660 27080 21000 24550 57380 45700 56370 67080
size L 31020 22740 26320 9970 9620 12780 14030 23440 14800 22610 21380
size M 4760 4090 4510 3550
Total gross returns 56600 45470 51030 32630 36700 33780 38580 85580 64590 83490 92010

Preharvest cost 16145 14920 14900 16145 15060 15030 15190 18010 15750 15850 16070
Harvest and marketing cost 23180 18520 20820 12990 14530 13560 15460 26560 19980 25900 28370
Total cost 39325 33440 35720 29135 29590 28590 30650 44560 35730 41750 4450

Net returns 17275 12030 15310 3495 7110 5190 7930 41020 28860 41740 47560

*gross returns are based on the following prices received for 25-lb cartons:
2001: size XL – $9.00, size L – $8.00
2002: size XL – $9.00, size L – $8.00
2004: size XL – $11.50, size L – $10.50, size M – $10.00

While all returns were positive, cover crop systems were less profitable than the MC-33 system in 2001/02, but in 2002/03 and 2003/04 cover crop systems were more profitable than the MC-33 system. Among the cover crops, sunn hemp appeared to produce the best results. In years when the sunn hemp treatment was used, it brought in the highest net returns of all treatments.
Use of cowpea, sunn hemp, and velvet bean cover crop systems appears promising. It is encouraging to obtain marketable tomato yields from these cover crop treatments that are equal to or better than those obtained with MC-33. In addition to the favorable economic results obtained here, cover crop systems offer several advantages to growers, and the environment that have not been quantified in the economic calculations presented here, and are not available with the MC-33 system. These benefits include the addition of organic matter to the soil, which enhances soil fertility and biological activities of soil microorganisms, and improves water holding capacity and water use efficiency (Brandi-Dohrn et al., 1997; Karlen and Doran, 1991, Wang et al., 2005). Not using fumigants also contributes to greater biological activity in the soil, and improved soil ecosystem functioning.
In our opinion, the results in Table 6 of Publication No. 1 represent a minimum economic value of cover crop systems, given other economic benefits that remain unaccounted for in this analysis. We recognize that the tests were not performed in soils with high nematode populations that would provide a rigorous challenge to the cover cropping systems. Therefore we suggest that additional experiments in future be carried out in soils more heavily infested with major pathogen, nematode and weed populations than the soils of the present experiments.

Farmer Adoption

In 2005, a partner in one of the largest tomato producers in Miami-Dade County indicated that the firm was implementing the automated soil moisture drip irrigation system in some of its tomato production operations. This system is being evaluated at the Tropical Research and Education Center for use in irrigating avocadoes, papayas, herbs, and palms.

A number of growers have expressed considerable interest in the use of cover crops, especially sunn hemp. Sunn hemp has been adopted for use by several small organic farm firms in Miami-Dade County. However absolutely no sunn hemp seed was available in the US during 2005 and most of 2006. Nevertheless late in 2006 sunn hemp seed was imported by Kauffman Seeds, Haven, KS, so it use may soon surge. Sorghum sudangrass is being grown on about 20% of vegetable land during the rainy summer season. The main factor which militates against the use of cover crops in Miami-Dade County is that most of the land in vegetable production is owned by landlords who issue one-year leases on most parcels. Thus growers are reluctant to make any investments in the land rented for only on year, since they have no assurance that they will reap the benefits. Sweet corn growers do not plant sorghum sudangrass because of the commonality of pests of this cover crop with those on corn.

Most compost is produced in Palm Beach County, so that it must be trucked about 100 miles for application in Miami-Dade County. Large commercial vegetable production firms are not convinced that the benefits of compost are sufficient to justify the cost of transportation. (We think this objection will be overcome after we have conducted an economic analysis of the joint use of an organic and plastic mulch in lieu of MC-33 and plastic mulch.) However the interest in the use of organic amendments and cover crops by owners of small firms engaged organic or sustainable farming has grown sharply. Since 2003 when this project began, the small growers have formed a “Community-Supported Agriculture Association” known as Redland Organics with the following internet site: http://www.redlandorganics.com/ . Four of these small firms produce their own compost in compliance with USDA National Organic Standards. Interest in organic farming and certification has surged in recent years. Since January 1, 2007 two 2 workshops on organic farming have been conducted in Miami-Dade County.

Factors likely to drive adoption of technologies evaluated in this study in the next years are (1) the burgeoning interest in organic production driven by the retail vegetable market, which pays a premium for organic, (2) the loss of methyl bromide, and our demonstration that soil fumigation is not essential on much of the acreage in Miami-Dade County, (3) the pressure to adopt Best Management Practices in vegetable production throughout all of Florida, (4) the recent requirement that all users of water in south Florida must pay for it, and (5) our study which shows that the joint use of organic and plastic mulch can result in far higher yields than the standard commercial practice of soil fumigation and use of plastic mulch.
With respect high-residue cover crop mulch for weed management in organic no-till potato production systems, based on the 2004-2005 data, previous and current research, and interest expressed by many growers, we are confident that organic farmers can use high-biomass cover cropping systems to simultaneously produce profitable potato yields and maintain or even improve soil quality. Although unavailability of appropriate no-till potato seeders is the major factor limiting adoption in the United States, shallow incorporation of cover crops on raised beds and using conventional seeders constitute a viable alternative that is currently being explored by growers in several countries, e.g. Germany, South Africa, etc..

Overall, the data are very encouraging. The work in 2005 and 2006 with strip intercropping (zone seeding) of cover crops and shallow incorporation of winter-killed cover crops (forage radish, sunn hemp, lablab, bell bean, etc.) and over-wintering cover crops (crimson clover, etc.) on raised bed tops (grow zones) has tremendous potential for both organic and conventional potato growers (see page 8, third paragraph, and page 9, last paragraph of Morse, 2007.

Recommendations:

Areas needing additional study

1.The main reason that the biologically based system of tomato production described herein does not qualify as an alternative to methyl bromide is that it is not capable of strongly suppressing high densities of either yellow or purple nutsedge. Thus a practical biological control system is needed, and this might be based on growing the nutsedge pathogen, Dactylaria Higginsi, in situ on cover crop residues.

2.The mechanisms whereby by growing a dense cover crop followed by the joint use of an organic mulch and a plastic mulch result in higher pepper yields than the standard commercial practice of fumigating the bed with methyl bromide and chloropicrin under a plastic mulch need to be elucidated. Also an in-depth economic analysis of this alternative production system should be conducted. Finally this system needs to be evaluated in fields that have very dense nutsedge infestations.

3.The relationship of water tension in raised beds to yields of tomato and pepper should be quantified.

4.Calibration of the solid state soil moisture probes need to be simplified for use by growers.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.