Soil solarization and winter and summer cover crops were evaluated as strategies for reducing synthetic chemical inputs in vegetable production systems. Studies were conducted at Louisiana State University Agricultural Center and Southern University and on two cooperating farms. Results suggest that the utilization of soil solarization can be feasible. Weed control was generally greater with annual broadleaf weeds and some grasses than with nutsedge. Using southern peas as a summer cover offers an added incentive of allowing some economic return if some of the peas are harvested before incorporation. Winter cover crop utilization can be beneficial, but can require careful management.
- Initiate work with participating farmers in selecting sustainable agricultural research and demonstration projects by conducting a start-up workshop.
Establish on-campus and on-farm research experiments in sustainable production practices related to the utilization of cover crops and soil solarization practices that are suitable to the Gulf South region.
Conduct a minimum of six on-farm demonstrations and workshops to enable growers to visit one another’s research plots.
Provide scholarships for limited-resource growers to participate in sustainable agriculture conferences.
Strengthen the information exchange network among farmers and agricultural institutions in Louisiana through farmers’ markets and the newly formed Louisiana Sustainable Agriculture Working Group.
In most areas of the country, there has been a steady decline in the number of family farms, punctuated by losses due to weather-related crop failures and record low commodity prices. As a group, small family farms have fared even worse as has been documented in the USDA National Commission on Small Farms Report. In southern Louisiana, however, there has been a recent resurgence in small-scale, fresh-market production of fruits, vegetables, and culinary herbs for local markets. The recent establishment of several farmers’ markets such as the Red Stick Farmers’ Market has greatly contributed to this trend. However, many of these growers do not come from traditional horticultural (i.e. fruit and vegetable) farm backgrounds, and many are limited resource farmers who receive little or no technical support within the region.
At present, local production of fresh-market fruits and vegetables falls far short of consumer demand. This creates an opportunity for more farmers to enter the local fresh-market farm economy, including those who are transitioning from the production of large-scale agronomic crops (i.e. row crops such as soy beans, corn, wheat, and sugar cane), and those who are interested in farming for the first time.
Consumer preferences lean heavily towards reduced-input (i.e. pesticide free, biologically farmed) and organic production practices. Information about such practices is very limited in the region because the majority of extension personnel at most 1862 land-grant universities traditionally serve high-input, capital- intensive horticulture operations for the wholesale market. Furthermore, the subtropical climate and related disease, insect, and weed pressures of our region complicate the transfer of sustainable practices from elsewhere in the country given our relatively unique conditions. Limited-resource growers need applicable information about such practices to realize greater profit through reduced dependence on off-farm inputs, the production of a more highly-marketable crop, and a healthier environment.
Farmers and agricultural professionals need to be knowledgeable of sustainable production systems that are economically profitable, environmentally viable and socially just. The use of summer and winter cover crops can benefit growers by reducing soil erosion, increasing soil fertility and decreasing pest populations. Soil solarization is another strategy that can reduce weeds, soil-borne insects and plant pathogens by heating soil that is covered with plastic mulch. In spite of the potential benefits that these strategies offer, farmers in Louisiana are often slow to adopt such practices, in part because working models and sources of information are often lacking.
This project sought to evaluate and increase awareness of sustainable practices suitable for small-scale vegetable growers. This initiative was based upon partnerships among area growers, the Baton Rouge Economic and Agricultural Development Alliance (BREADA), Southern University, LSU Agricultural Center, and Louisiana State University.
Materials and Methods
Objective 1: Start-up Workshop
A workshop was held Tuesday, June 13th 2001 for all members of the SSARE project. University participants, farmer participants and the project director from BREADA met with the goal of reviewing the project goals and the role of participants. Specific project activities were delineated, and an invitation was extended to meet at the Farmer Participant Informational and Planning Session to be held later.
Objective 2: Establish On-Campus and On-Farm Research Experiments
Research plots were established at the Louisiana State University Agricultural Center (LSUAC) Burden Research Center and Southern University Horticultural Farm. A graduate student research assistant and student worker were hired to work on the project at LSUAC with the winter cover crops and the solarization project. A research associate, to be housed at Southern University, was to be hired to assist in all aspects of the project including coordination of research and demonstration activities, plot establishment at both SU and LSUAC and on-farm demonstration/research as well as provide technical support for workshops. The research associate was not hired for the project, however a research associate in the Department of Horticulture LSUAC (not funded on this project) assisted with implementation of research activities at the LSUAC Burden Research Station in Baton Rouge. Research associates at Southern University also assisted with the research initiative at Southern University and with two on-farm research sites.
Winter Cover Crops Studies (Louisiana State University Ag Center)
Winter cover crops were established during the last week of October (2000, 2001) at LSUAC for spring production of watermelon and jalapeño pepper. Cover crop treatments consisted of three raised beds 30 ft long on four ft centers. Crimson clover and annual ryegrass “Gulf” were planted using “Stanhay” belt planters at 11.5 and 13 lb per acre, respectively. Seed was drilled in rows in the raised beds and in the row middles. Plots received supplemental overhead irrigation after seeding to enhance stand establishment.
Non-cover crop plots (bareground) were used for comparison purposes. Bare ground plots were treated with a mixture of Gramoxone 2.5L (2 pints per acre) and Goal 2 XL (1 pint per acre) for weed suppression during the winter. All plots were fertilized preplant with 400 lb. per acre of a 8-24-24 banded into the beds in the fall following soil sampling and commercial fertilizer recommendations.
The following were the winter cover crop and spring planting treatments for watermelon and jalapeno pepper crops (Table 1).
Table 1. Winter cover crop treatment followed by spring cover crop management and vegetable production.
Cover crop treatment—–Cover crop management —– Vegetable crop production
Cover crop ——- Herbicide application/rolling — no-till through cover crop residue
Cover crop ——- Incorporated cover crop ——— no-till through bare ground
Bare ground —————- —————bare ground, conventional production
Bare ground ———- —————– plastic mulch, conventional production
Spring cover crops management and vegetable crops mulch.
Winter cover crops were managed in the spring (last week of March) two ways: by incorporation of cover crop residues for bareground planting, or, herbicide application and rolling residues flat prior to no-till planting. Cover crop incorporation was accomplished by cutting with a flail mower and incorporating the cover crops residue using discs followed by rototilling. Breakdown of cover crops residues for both years was slow due to high plant biomass and also low soil moisture. The incorporation of residues took several weeks to achieve.
Preparation of the cover crops for no-till planting was accomplished by spraying the cover crop with an application of glyphosate (Roundup 4L, 1 quart per acre) followed by rolling down the cover with a roller bed-shaper a week after spraying. The incorporated winter cover crop and the bare ground treatment used raised beds and trickle irrigation tubing in the bed. For the black plastic mulch treatment, mulch was installed prior to planting with trickle irrigation tubing installed at a 3-inch depth off center.
Nitrogen Fertility Management
To evaluate the effect of fall cover crop treatments on nitrogen management, cover crop plots were subdivided in three subplots, each of which was fertilized with either 0, 50 or 100 lb/A of ammonium nitrate (33-0-0) plus 100 lb/A of potassium chloride (0-0-60). Plants were watered and fertilized using drip irrigation.
Five week old watermelon seedlings were hand-transplanted into the field plots during the third week of April at 3-ft in-row spacing on 8-ft centers. “Sangria” transplants were used on the center (record) rows and “Sugar Baby” was used on the side (guard) rows of each plot. Weeds were controlled by application of ethalfluralin (Curbit 3 EC, 3 pints per acre) in non-mulch plots and incorporation using overhead irrigation (0.5 inch). Sethoxydim (Poast 1.53 EC, 4 quarts per acre) was applied postemergence broadcast later in the season (twice) to control grasses in all the plots.
Four week old jalapeno pepper transplants were hand-transplanted into field plots the end of April at a 2-ft in-row spacing on 4-ft centers. “Mitla” jalapeno transplants were used on the record row and the guard rows. Weeds were controlled by application of trifluralin (Treflan 4 EC, 1pint per acre) in non-mulch plots and incorporation using overhead irrigation (0.5 inch). Sethoxydim (Poast 1.53 EC, 1 pint per acre) was applied postemergence broadcast later in the season (twice) to control grasses in all the plots.
Solarization Studies (Louisiana State University Ag Center)
Field studies were conducted during the summer/fall seasons of 2001, at the LSU AgCenter Burden Research Center, Baton Rouge, Louisiana, U.S.A. Experiments were conducted to evaluate the effect of strip soil solarization strategies on the production of fall planted lettuce. Solarization strategies (treatments) were designed to test summer solarization combined with fall plastic mulch treatments using low-density polyethylene films. Treatments are listed in the table below.
Soil temperatures under the solarization mulch as well as bare ground were recorded for the solarization period and weed pressure was noted for all treatments. In the fall, clear and black plastic (summer solarization treatments) were left in place (Trt 4, 6). Other treatments were installed: black plastic mulch (Trt 2), and black plastic mulch plus fumigation (Trt 3). In addition, clear plastic from summer solarization was painted black (Trt 5). Bare ground during solarization and the fall crop season served as a control (Trt 1). Lettuce transplants were hand-transplanted into double rows on raised beds. Four lettuce cultivars were used in the study.
Three summer solarization strategies were evaluated for fall-planted lettuce at the Burden Research Station, Baton Rouge, Louisiana.
The following are the treatments:
Treatment Summer solarization Fall crop season
Bare ground Bare ground
Bare ground Black plastic
Bare ground Black plastic + fumigation
Solarization: clear plastic mulch Clear plastic
Solarization: clear plastic mulch Clear plastic + black paint
Solarization: black plastic mulch Black plastic
The last week of June raised beds were made at the LSU Agricultural Center Burden Research Station for the summer strip-solarization treatments. Either clear or black plastic mulch (48 inch wide, Climagro, Quebec, Canada) were installed with trickle irrigation tubing in the center of the bed. A summer bareground, or fallow treatment was used as a control. Experimental plots consisting of three beds 30 ft long were randomly assigned to the treatments above.
Beds were on 4 ft. centers with a 9 inch height and 14 and 21 inch width at the top and bottom of the bed, respectively. Row middles of all treatments and beds on bare ground plots were kept weed-free with a mixture of pronamide (Kerb 50% WP, 3 lb per acre) and paraquat dichloride (Gramoxone Extra 37 %, 2.37 L per ha). Two plantings of four lettuce cultivars: ‘Buttercrunch’ (Harris, Rochester, New York), ‘Two Star’ (Orsetti, Hollister, California), ‘Tania’ and ‘Waldmanns Dark Green’ (Harris Moran, Modesto, California) were evaluated in the field studies. Buttercrunch and Tania are Bibb and Butterhead-type cultivars, respectively, while the others are loose-leaf type cultivars. Treatments and varieties were assigned to experimental units following a split-plot design, with treatments as main plots and varieties as subplots.
Polyethylene films were 4 ft. wide and 0.038 mm thick. Black and clear films (Climagro, St-Laurent, Quebec) were installed over pre-shaped beds using a plastic mulch layer (Kennco, Ruskin, Florida), with a single line of drip irrigation tape (Turbulent Twin-Wall, Chapin Watermatics, Watertown, New York) buried 3 inch. deep in the center of the beds. Clear (Trt 3, Trt 4) and black (Trt 5) solarization films were installed on 26 June and 24 July for the first and second plantings, respectively. These films were kept in place through the fall growing season. Fall mulch treatments (Trt 2, Trt 3) were installed on 19 Sept. and 10 Oct. Before crop planting, mulch on treatment Trt 4 was painted black using a backpack sprayer to cover the films with 43% v/v dilution of oil based paint in mineral spirits so that it was opaque.
Fall crop season:
Three week old lettuce transplants were hand-transplanted into field beds on 21 Sept. and 20 Oct., 2001 in staggered double rows at 10 inch between rows and 12 inch in-row spacing. Based on soil sampling and commercial fertilizer recommendation, pre-plant fertilizer (8N–24P–24K) was applied at 560 lb per acre before planting in bare ground plots, and before film installation in the rest of the treatments. Nitrogen was supplemented with 270 lb per acre ammonium nitrate administered in weekly intervals through the irrigation system. Irrigation was applied daily when soil tensiometer (Irrometer, Co., Riverside, CA) readings at a 10 inch depth reached – 0.2 mPa and terminated at -0.1 mPa. The soil was an Olivier silt loam (Typic Paleudults).
Soil temperatures were measured 2 and 4 inch. below the top of the bed for each treatment on two blocks for both plantings. Copper-constantan double insulated thermocouples and a CR10X data logger (Campbell Scientific, Logan, Utah) were used to collect the data. Average hourly temperatures were measured and recorded for 53 days for the first planting and 34 days for the second planting during the summer solarization periods.
Plant survival and the incidence of soil borne diseases were evaluated weekly. Lettuce plant growth and physiological problems and the incidence of insects and weed pests were monitored. Lettuce harvest was on 25 Oct. and 21 Nov., 2001 for the first and second plantings, respectively. Plants were harvested when they reached an appropriate size, or left to be harvested on subsequent dates (29 Oct., 2 Nov. and 6 Nov. for the first planting, and 26 Nov. and 30 Nov. for second planting). Fresh weight was recorded individually for heads harvested from 10 plants from the center bed of each subplot.
Cost budgets were estimated for each treatment based on projected costs for Louisiana vegetable crops. Budgets were modified for small operations with a high technological level, and included costs for soil preparation, pest management and cultural practices. Costs associated with soil solarization, fall-mulching and supplemental pest-control were added as required by each treatment. Lettuce yields required to cover production costs (breakeven yields) were calculated for each treatment, assuming a price of US$ 5.45 per box of 24 heads. Relative increases in breakeven yields required to cover the differences in costs between bare ground (solarization and fall planting) and bare ground followed by plastic mulch and the rest of the treatments were also calculated.
Summer Cover Crop Studies (Southern University)
Plots were established to evaluate the performance of southern pea (Vigna unguiculata) as a summer cover when various harvesting and incorporation strategies were utilized. The study was conducted over a two year period. ‘Mississippi Silver’ southern peas were planted on 30 May, 2001 and on 26 July, 2002. Seeds were planted in three row plots measuring 40 feet long on four feet centers. Rows were established approximately six inches high. Within-row plant spacing was approximately 6 inches. All data were taken from the middle row of each three-row section. Peas were mowed in place with a 4 hp Garden’s Ways Trail Blazer sickle bar mower at bloom, and after the first and second harvests during 2001 and at bloom, after the first, second and third harvests during 2002. Fallow plots were established without the benefit of cover crop. The 40 feet sections were divided in half with each half dedicated to either broccoli or lettuce. Half of the plot for each crop received 13-13-13 fertilizer at the rate 575 lbs per acre and half received rabbit manure at the rate of 5 tons per acre. During the second year, Agreaux 3-3-3 chicken manure based fertilizer (approved for organic production) was used instead of the rabbit manure at the rate of 1.25 tons per acre.
Greenhouse-grown transplants were used for each crop. ‘Packman’ broccoli was planted during both years. ‘Simpson Black Seeded’ lettuce was planted in 2002 while ‘Red Sail’ lettuce was planted in 2003. Lettuce and broccoli transplants were seeded on 27 August and planted in the field on 4-5 October in 2001. Crops were planted in eight foot sections in double rows and with in-row spacing of twelve inches. There were four replications. Lettuce was harvested on 28 November 2001. Brocolli was harvested on three occasions between 28 November and 7 December, 2001. All yield data were taken from the center row of the three row plot.
Seeding for broccoli and lettuce transplants was done on 4 September and 16 September, respectively in 2002 while transplanting was done on 10 October. Both crops were harvested on 16 January, 2003.
In 2001, Chlorophyll readings were taken from three leaf samples from each broccoli plot with a Minolta SPAD 502 chlorophyll meter. The three readings were then averaged. Data were analyzed as a randomized complete block experiment with a factorial arrangement (4 by 2 in 2002 and 5 by 2 in 2003).
Soil Solarization Studies (Southern University and Cooperating Farmers)
In 2000, a field experiment was established at the horticultural farm at Southern University to evaluate the following treatments:
plastic on flat bed with manure rabbit manure applied (at 5 tons/acre);
plastic on raised bed with manure applied
plastic on flat bed with 13-13- 13 applied at 770 lbs. acre
plastic on raised bed with 13-13-13 fertilizer applied at 770 lbs/acre
fallow plots with 13-13-13- fertilizer applied.
Each plot measured 12 by 15 feet. Three rows approximately 6 inches high were established in plots that had raised beds. Plastic was applied by hand in order to cover row middles. There were five replications.
Soil temperatures were monitored in the raised and flat beds plastic covered plots with Fisher soil thermometers. Plastic was removed on 10 November and beds were prepared for planting for a winter collard crop. Plots were rototilled and bedded prior to planting and shallow cultivation and hipping was required of the plots in which beds had been previously raised . “Vates” collards were direct seeded using a Planet Junior push planter on 15 November. Seeds germinated slowly, and an extremely cold winter led to very poor plant performance, and meaningful yield data were not obtained. . “Sugar Baby” watermelons were planted in the same plots on 20 June, 2001 from transplants seeded on 17 May, 2001. Fertilizers were added at the rates indicated above. Within row spacing was approximately 2.5 feet. On 24 August, melons were harvested and weighed from each three-row plot, and soluble solid percentages were obtained from three melons from each plot using a Bausch and Lomb table refractometer.
On-farm research plots were established on one conventional (Matthew Byrd Farm) and one organic farm (Food for Thought Organic Farm). These experiments were established via a SARE producer grant but were linked with this current initiative. Treatments on the organic farm included flat plots with rabbit manure applied at 5 tons/acre, flat plots with no manure applied, raised plots with manure applied, and fallow plots. There were five replications. Plastic was applied by hand on July 27, 2000 to plots that measured 12 by 15 feet. Plastic was removed on 28 November 2000. All weeds from the 12 by 15 foot section of the solarized plots were harvested and weighed. Manure was then applied to flat and fallow sections that had not previously received manure. ‘Packman’ broccoli transplants were planted on 2 December 2000 from transplants seeded on 20 October. Earlier planting was delayed because of excessive rains in November. Broccoli was harvested on 2 February 2001. Data were taken from the center row of the three row plot.
Treatments at the conventional farm were as follows: flat plots with rabbit manure applied at 5 tons/acre, flat plots with 13-13-13- fertilizer applied at 770 lbs/acre, raised plots with 13-13-13 fertilizer applied at 770 lbs./acre and fallow plots. Weeds were harvested and weighed on 1 November 2000. ‘Rio Verde’ cabbage was to be planted during the late fall, 2000. (Mr. Byrd, the cooperating farmer, became ill and evidentially died prior to the completion of the project.)
Studies at Louisiana State University AgCenter
Winter Cover Crops Studies
The amount of aerial plant material in the winter cover crops study was evaluated for each plot at the time of killing the cover crop in the spring. Dry weight of residue ranged between 1.3 and 6.1 ton per acre, with an average of 3.0 ton per acre. Most of the residues in the plots were from annual ryegrass, which appeared to suppress crimson clover growth. Ryegrass and clover were direct seeded the same week in the fall. Rye grass, however, emerged quickly, outgrew the clover, and quickly established a plant. At the end of the winter season, the majority of biomass in the cover crops was rye grass.
Watermelon growth was measured during the last week of May. The results suggest that vine length was not affected by nitrogen fertilization. There was a difference, however, in vine length between the plastic mulch and the other treatments:
Treatment Vine length (inches)
Plastic mulch 80.7
Cover Crop (incorporated) 53.8
Cover Crop (no-till) 48.6
Bare Ground 48.5
Longer watermelon vines in the plastic mulch treatment is probably attributed to higher soil temperatures with this treatment as watermelon is a warm season crop and responsive to enhanced temperatures. The cover crop and bare ground treatments, had lower soil temperatures in general, and this probably contributed to shorter watermelon plant vines with these treatments.
Spring Vegetable Crops
Due to heavy rainfall and flooding in the fields in late spring caused by tropical storms both years, reliable yield data for both jalapeno and watermelon crops could not be gathered. There appeared to be a trend, however, of increased earliness of plastic mulch compared to the other treatments ie. no-till and incorporated cover crop treatments.
Solarization significantly increased soil temperatures compared to the bare ground control.
The increase in temperatures were similar for clear and black mulches. The time occurrence of minimum temperatures above 99 F was longer for the transparent mulch, suggesting that clear films may have greater potential for pathogen control. The highest soil temperatures for black mulch, however, occurred approximately 20 minutes earlier than those for clear film.
Lettuce plant stand was not significantly affected by treatment or cultivar. Few plants in record rows were lost during the experiments and no plants showed disease symptoms. Use of plastic mulch increased head weight, regardless of the solarization treatment, compared to the bare ground treatment. Soil solarization increased the yield of lettuce by enhancing plant growth as evidenced by higher head weight compared with lettuce grown on plastic mulch installed in the fall. In addition, soil solarization significantly reduced weed populations, especially those of grasses. Enhanced weed suppression was achieved by using black plastic for solarization and mulching. Increased break-even yields of 15 to 30 percent were found in order to cover the additional expenses of solarization compared to bare ground.
Southern University and On Farm Studies
Little difference was noted in temperatures obtained from flat and raised solarized beds on the SU Horticultural Farm. For the flat beds, temperatures ranged from 1.05.8 to 131 F at a depth of 2 inches and 89.6 to 107.6 F at a depth of 8 inches. Temperatures from the raised beds ranged from 109.4 to 131 F at 2 inches and 89.6 to 105.8 at 8 inches. Mean temperatures for each set were almost identical with approximate 117 F and 97 F for the 2 and 8 inch depths respectively.
No statistically differences were noted in the ‘Sugar Baby’ melon yields, and results are summarized as follows:
• Flat plots with manure before solarization- 16.0 tons/acre
• Flat plots with 13-13-13 applied- 14.2 tons/acre
• Raised plots with manure before solarization 12.4 tons/acre
• Fallow plots with 13-13-13 applied. 11.8 tons/acre
Percentage of soluble solids ranged from 8.1% for the flat/manure treatment to 6.9 % for the flat/conventional fertilizer treatment, but again, these results were not statistically significant. The inclusion of more replications may have resulted in these difference being significant.
No significant differences were found in the amount of weed left after solarization for any of the solarized plots at the two on-farm sites. Of course, much more weed was noted in the fallow plots, but these data were not included in the statistical analysis since it was assumed that all of the solarized plots would contain significantly fewer weeds. There were some weeds present along the edges of the plastic and along the middles between rows of raised beds. Some of this growth occurred in the fall during cooler temperatures.
On the conventional farm , fresh weight of weeds per 12 X 15 ft. section ranged from 9.3 to 13.9 lbs. fresh weight while on the organic farm, fresh weight of the remaining weeds ranged from 7.7 to 9.6 lbs fresh weight. On the organic farm and at the SU site, most of the weeds remaining were grasses and sedge, while in the fallow plots, there was a mixture of broadleaf and grasses. It should be pointed out that much of the weed growth occurred during late summer and early fall, when temperatures dropped. The solarization was not as effective with the nutsedge, probably due to the existence of reproductive tubers at greater depths than annual weed seeds. It should be noted that the conventional farm had a serious infestation of Johnson grass, which was greatly reduced with the solarization process.
Brocolli yields were greater affected by extremely cold winter temperatures during parts of the growing season. However, there were significant differences in yield data obtained. Both the flat and raised plots that received manure prior to solarization out yielded the fallow plots that received manure after solarization. Yields were as follows:
• Flat plots with manure before solarization- 1.5 tons/acre
• Raised plots with manure before solarization- 1.4 tons/acre
• Flat plots with manure after solarization 1.1 tons/acre
• Fallow plots with manure added just prior to planting. 0.7 tons/acre
Summer Cover Crop Study
Yield of broccoli and lettuce for 2001 were both greater than yields obtained following the 2002 cover crop because of excessive rain during the latter growing season. Harvests were delayed because the crops grew slowly. In 2001, significant yield differences occurred between broccoli plots receiving conventional fertilizer and manure. Plots receiving the fertilizer averaged 3.4 tons/acre while those receiving the manure averaged 2.0 tons/acre. Chlorophyll readings suggested a difference in nitrogen content. The conventional treatment averaged 70.0 Spad units while the organic treatment averaged 60.7 units. Cover crop strategies did lead to significant difference among treatments, but fallow plots tended to yield less marketable broccoli. Results are summarized below:
Southern pea cover management Broccoli Marketable Weight (2001)
Incorporated at full bloom 2.9 tons/acre
Incorporated after one harvest 2.7 tons/acre
Incorporated after two harvest 2.7 tons/acre
Fallow plots 2.3 tons/acre
Broccoli plots receiving the organic and conventional fertilizers yielded 1.6 and 1.2 tons/acre respectively in 2003, but yields were not significantly different. Thus, the pulletized chicken manure performed comparably with the conventionally fertilizer. No significant differences resulted from the cover crop treatments, which are summarized below.
Southern pea cover management Broccoli Marketable Weight (2003)
Incorporated at full bloom 1.8 tons/acre
Incorporated after one harvest 1.7 tons/acre
Incorporated after two harvests 1.4 tons/acre
Incorporated after three harvests 0.8 tons/acre
Fallow plots 1.1 tons/acre
With lettuce, no statistical differences due to fertility were found in either year with marketable yields averaging 8.0 tons/acre for the conventional treatment and 7.9 tons/acre for the manure treatment in 2001. Yields for lettuce harvested in January, 2003 tended to be higher for the organic treatment, although yields for both treatments were substantially lower for reasons cited earlier. However, these results were nearly significant (p=0.0589). Yields for the conventionally and organically grown lettuce were 1.4 tons/acre and 1.9 tons/acre, respectively. Cover crop effects from both years are summarized below:
Southern pea cover management Lettuce Marketable Weight Lettuce Marketable Weight
Incorporated at full bloom 8.8 tons/acre 1.6 tons/acre
Incorporated after one harvest 7.8 tons/acre 2.0 tons/acre
Incorporated after two harvests 7.6 tons/acre 1.6 tons/acre
Incorporated after three harvests —— 1.9 tons/acre
Fallow plots 7.7 tons/acre 1.2 tons/acre
Although the above cover crop results are not significant, lettuce yields from the previously fallow plots were numerically lower than all or most cover crop treatments, thus suggesting a possible trend.
Nitrogen fertility may have affected the results in the summer cover crop study. Because broccoli is more demanding of nitrogen, higher rates of manure were probably needed than were applied. However, yield results suggest that there was sufficient nitrogen for the lettuce fertilized with manure to perform comparably to the conventionally fertilized lettuce. In the second year of the study, although yields were reduced because of unfavorable weather conditions, the palletized chicken manure fertilizer performed comparable to the conventional fertilizer. Results also suggest that yields of vegetables from plots with the summer crop can be equal to or greater than previously fallow plots, even after one or more harvests of the southern pea cover crop. Thus the farmer can receive a double benefit from using such a cover crop.
A field day was held on July 18, 2001 at the LSUAC research station. Cover cropping, both summer and winter, as well as solarization research was demonstrated at this workshop.
Objective 3: On-Farm Demonstrations and Workshops
Three on-farm demonstrations were completed and mini-workshops conducted with solarization and summer cover crops studies. Solarization plots were established on one conventional and one organic farm. Winter cover crop demonstrations were also established on these farms.
Objective 4. Scholarships for limited-resource growers to participate in sustainable agriculture conferences
Scholarships were offered to limited-resource growers to participate in sustainable agriculture conferences ie SSAWG. Unfortunately, only a few of the growers were able to take advantage of the scholarships. A majority of the growers affiliated with the project have family owned and operated farms and are involved in direct sales at farmers’ markets. Unfortunately, these obligations preclude them from attending out-of-town conferences.
Objective 5. Strengthen the Louisiana Sustainable Agriculture Working Group (LaSAWG) as a means of information sharing and dispersal.
The executive director of BREADA (SSARE Project Coordinator) worked with the executive board of LaSAWG to strengthen the information exchange network among farmers and the various agricultural institutions in Louisiana. A listserve for members was developed to assist in coordinating an annual meeting. The annual meetings served as mechanism to share on-farm and university research findings as well as to discuss collaborative efforts.
Educational & Outreach Activities
- Julio Hasing – M.S. Horticulture, Louisiana State University, 2002. Thesis: Agroeconomic Effect of Soil Solarization on Fall-planted Lettuce.
Hasing, J.E. and C.E. Motsenbocker. 2002. Effect of summer solarization on the yield and economics of fall planted lettuce. International Horticultural Congress Meeting, Toronto, Canada (Abstr. On site Program: 294)
Julio E. Hasing, Carl E. Motsenbocker, and Charles J. Monlezun. Agroeconomic effect of soil solarization on fall-planted lettuce (Lactuca sativa). Submitted to Scientia Horticulturae (a refereed publication).
In addition, Dr. Owusu Bandele included information regarding the solarization and cover crop projects in presentations made at several workshops and seminars including:
The Black Farmers and Landowners 4th Annual Meeting, Atlanta, Ga, Feb., 2002
USDA/AMS and SU sponsored Project United Export Workshop, Tallulah, LA, Feb., 2002
Organic Production Workshops, El Salvador, Sept., 2001
Organic Production Workshop, SU, Aug., 2002
USDA/NRCS sponsored small farmers workshop, Aug., 2002
Annual Louisiana Extension Training Conference, Dec., 2002
The use of summer solarization for fall-planted lettuce indicates that solarization followed by fall planting is economically feasible. Crop production, however, may be severely impacted in soils with severe pest infestation. Additional evaluation is required to investigate the benefits on pest management.
Soil solarization could have applicability for conventional farmers, for example strawberry growers who are seeking alternatives to methyl bromide. However, many of these farmers would probably opt to use conventional herbicides to control weeds between and around the raised beds. Organic farmers would also have to contend with weeds between the beds if the plastic is applied only along the row. Therefore, they would have to mulch these areas, or apply the plastic over the entire area. This would necessitate manual application of the plastic, and would therefore be more suitable for smaller areas since it would not be feasible to manually apply the plastic over larger land areas.
Winter cover crops provide benefits to crop production sustainability. Management of cover crop residues in the spring, however, can be problematic due to weather that can impact timing for production of spring vegetables.
Southern peas are an important crop to many growers in the region that sell at farmers’ markets and at roadside stands. Although cover crop effects were not significantly different, trends were noted that suggested that southern peas as a cover crop could enhance marketable yields, even when some of the peas were harvested before incorporation. Thus, farmers would more likely use this summer cover since some income could be derived from the harvested peas before incorporation as a green manure crop
Production costs for experimental treatments are presented in Table 3.7 (see printed report). All treatments except for the bare ground control included costs for mulch installation and removal (plastic film, mulch layer, transportation and labor). Post-solarization mulch painting was included only in this treatment (T3) (boom sprayer, paint and solvent) and supplementary weed control costs were considered only for the bare ground treatment. All the remaining costs were included for all the treatments.
Production costs of strip-solarization treatments (T3 and T5) were $1235 and $490 higher than bare ground and fall-mulch cropping systems, respectively (see table 3.8 – printed report). The additional expenses translate into increases in break-even lettuce yields of 15.1% for bare ground and 5.4% for fall-mulch. Other researchers (Bell, 1998) reported that a 4.8% crisphead lettuce yield increase was required in order to cover solarization costs in conventional production in California, with a price of $7.79 per carton of 24 heads. In this study, solarization expenses comprised the cost of plastic film and its application and removal, and were estimated at $750 per hectare. Results from previous research suggest that the increases in lettuce yield required to cover additional expenses can be attained with soil solarization. Other researchers reported a 7 to 29% (Palumbo et al. 1997) and 90-113% (Campiglia et al., 1998) increase in lettuce yields due to soil solarization. A relatively low, wholesale price of $0.23 per head was utilized for the economic analysis, increases in breakeven yield are likely to be overestimated. Lettuce has been sold at prices as high as $1.50 per head in local farmers’ markets (unpublished data), one of the outlets available to small growers for whom the experimental budgets are representative. Other potential markets for such growers include produce stores and restaurants, and they are also likely to pay prices above wholesale for small volumes of product.
Soil solarization increased the yield of lettuce by enhancing plant growth as evidenced by higher head weight. Since lettuce is marketed by units and not by weight, this increase does not have a direct short-term economic impact. Solarization has shown to have long-term effects, however, such as pest suppression that can be reflected as cost reductions in the long run (Davis, 1991). Results from this study show that soil solarization significantly reduced weed populations, especially those of grasses. Solarization has the potential to modify the composition of the weed community over time, eventually affecting the requirements of weed management strategies.
The choice of transparent or black mulch has been previously investigated with mixed results (Abu-Gharbieh et al., 1991; Chase et al., 1999b; Campiglia et al., 1998; Campiglia et al., 2000; Ham et al., 1993; Rieger et al., 2001). In this study, mulch opacity did not directly affect yield. Temperature data, however, suggest that clear mulch has a slightly greater potential for controlling soil-borne pests. On the other hand, weed pressure was higher in soils solarized with clear mulch. Painting transparent mulch after the solarization period increased the populations of Cyperus spp. The short-term economic returns of solarization treatments are conditioned by pest pressure on agroecosystems. In this experiment, solarization did not exert an effect on marketable yield due to the lack of pest pressure. However, previous research suggests that increases in yield required to cover solarization costs are attainable.
Two farmers that participated in the project increased the utilization of summer and winter cover crops in their operations. Several other farmers at the Red Stick Farmers’ Market grow Southern peas in their operations, and the use of this crop as a summer cover will continue to be encouraged.
On-farm participation and farmer adoption was less than expected due to not hiring a Southern University research associate. This position was to be filled and supported with project funding, but was not.
Areas needing additional study
- Further evaluation of the value of solarization and cover crops production techniques on-farm.
Continuing on-farm and experiment station solarization research. In particular pest management and pathogen control with other crops as well as plastic opacity.
Economic evaluation of sustainable production technologies using solarization and cover crops.