Cropping Systems for Intensive Desert Vegetable Production

Final Report for SW98-044

Project Type: Research and Education
Funds awarded in 1998: $130,672.00
Projected End Date: 12/31/2001
Matching Federal Funds: $5,000.00
Matching Non-Federal Funds: $88,000.00
Region: Western
State: California
Principal Investigator:
Charles Sanchez
University of Arizona
Co-Investigators:
Dr. Milt McGiffen, Jr.
University of California
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Project Information

Abstract:

There has been an exponential increase in acres planted to organic vegetables in Arizona and California. The low desert area has many advantages that producers can use to exploit unique market niches. But the soils are exceptionally low in organic matter. We quantified what is often called “the organic effect”, i.e. the positive changes that result from the transition to organic production practices. The experimental fields in Thermal, California and Yuma, Arizona are in the major vegetable production area of the lower Colorado River desert. Two cover crops (cowpea and sudangrass) were compared to traditional summer fallow. Sudangrass was incorporated into the soil and cowpea was either incorporated or used as mulch (reduced tillage system). Cowpea mulch increased daily minimum soil temperature and decreased maximum soil temperatures, which may allow growers to extend their season into more profitable markets. In Year 1, yields for both melons and lettuce were lower when lettuce or melons were managed organically. In Yuma, AZ, lettuce and melon yields were always less for the organic treatments compared to the conventional treatments. For lettuce both insects and soil fertility limited yields in the organic plots. For melons the limiting factor in the organic plots was always insects.
However, organic yields equaled those of the conventional management system in Year 2 at Thermal, CA. Insect populations in Thermal, CA were generally lower across all years of study than in Yuma, AZ. Weed populations in Year 2 were reduced under organic management. Cowpea cover crops also decreased weed species diversity, with fewer weed species present following cowpea cover crops. No increase in insect pest populations were observed in the cover crop plots, indicating that they do not serve as an alternate host for pests. Cowpea cover crop significantly increased yield of fall planted lettuce and winter/spring planted cantaloupe. Cowpea cover crops require little water and no fertilizer, produce abundant biomass and nitrogen, and can reduce weeds and nematodes. Incorporating summer cowpea residues into the soil significantly increased yield for both conventional and organic management system. Growers have followed up on our results by increasing the acreage planted to cowpea cover crops from nearly zero in 1995 to several thousand acres and increasing.

Sudangrass increased the yield of cantaloupe, but not lettuce. Reduced lettuce yield following sudangrass was possibly due to nutrient immobilization or allelopathy from the cover crop residues. Our results strongly support the use of cowpea cover crops prior to fall planted lettuce in the desert. Additional investigations are needed on the benefits of sudangrass cover crop in a rotation where it precedes lettuce. A reduced tillage system using cowpea mulch reduced weed populations and provided nutrients to the fall crop. However, due to rapid residue decomposition in the desert, those benefits were not carried over to the spring cantaloupe crop.

Project Objectives:

1) Evaluate the effectiveness of cover crops in reduced tillage (surface mulch) and conventional tillage (incorporated) production .

2) Develop cost studies for desert for ICM and organic based vegetable production systems and compare those costs to conventional production systems.

3) Extend current knowledge of cover crop systems to vegetable growers, Soil Conservation Service, and other interested parties.

Introduction:

Production of winter vegetables is increasing in the low desert areas of southern California and southern Arizona. The Coachella Valley in southern California produces an exceptionally diverse variety of high value vegetable crops, including: lettuce, celery, artichokes, eggplant, sweet corn, bell peppers and melons (Riverside County Ag Commissioners’ Reports, 1995). In 1996 in Yuma County Arizona, winter vegetables were produced on 31,245 hectares of land and had a farm gate value exceeding 500 mil-lion dollars. Production of these high value crops in both locations is generally achieved through the rela-tively high input of fertilizer, pesticides, and irrigation water due to grower anxiety about crop quality and lack of sufficient information on alternative practices. The lack of practical technologies and data neces-sary to implement sustainable agricultural practices combined with the rigid market standards for produce limit grower willingness to embrace alternative production practices. Conversely, at this time of high in-put agriculture, organic crop production is suggested to growers as a possible production practice for de-sert areas due to reports of “skyrocketing” demand for organic produce (e.g. California Farmer May 1997 pp. 19-24). The ability of desert crop production areas to produce a winter crop could fill unique supply niches in the organic vegetable market when other areas of the country are unable. However, growers interested in trying organic techniques often note a lack of information applicable to local conditions due to limited studies on organic methods for desert crop production. In addition, cost studies are needed so growers can evaluate whether the higher market value for organic produce will offset the higher produc-tion costs associated with organic production practices.

There are many valid reasons to increase the use of sustainable on-farm cropping practices. Vegetable growers today need to be concerned as much with leaching nutrients into groundwater, the de-creased availability of pesticides for vegetable crops, and maintaining topsoil as with the economics of crop production. Among the sustainable practices now embraced by growers is the inclusion of cover crops into crop rotations. Desert vegetable production is well suited for cover crop use. Cover crops adapted to the heat can be planted in the summer so that biomass is produced between main crops when water costs are low. The role a cover crop can play in a vegetable crop rotation system is variable. First, the cover crop produced can be used as green manure when incorporated into the soil. The additional or-ganic material can improve soil fertility, soil structure, and increase soil organism bio-diversity. Addi-tionally, cover crops can be left on the soil surface as mulch to provide weed control and reduce soil water evaporative loss. However, growers need to know which cover crops are best for their system and how to integrate cover crops into the entire production system before they can obtain the benefits from cover crop use.

This research investigated two cover crops, sudangrass and cowpea in organic, ICM, and conventional production systems. Previous research by Walt Graves, an emeritus California farm advisor, has led to widespread interest in the use of cowpea as a summer cover crop. It is well adapted to desert heat and, as a legume, has the potential to add nitrogen to the system. Sudangrass a desert forage crop that shades out weeds and whose residues have an allelochemical effect on soil pests, is also well adapted to the heat and has the added benefit of producing a cash crop before the incorporation of the residue. In this proposed research, cowpea and sudangrass will be incorporated into the soil to study their influence as green manure on crop production. Also, a cowpea cover crop was left on the soil surface as mulch to study its influence on weed control and crop growth. In addition to the field data, an economic analysis of cover crop use in conventional, ICM, and organic production systems will be developed. This research, provided answers to grower questions on the economic and technological feasibility of organic production of winter crops for not only the Coachella and Yuma Valleys but it can be extended to include the Imperial Valley, northern Mexico, and the entire Lower Colorado River Valley.

Cooperators

Click linked name(s) to expand
  • Jose Aguiar
  • Sam Aslan
  • David Cudney
  • Michael Matheron
  • Jeff Mitchell
  • Mathieu Ngouajio
  • John Palumbo

Research

Materials and methods:

The effect of cropping system on crop yield, economics, pests, and soil factors were examined in a three-year field experiment at the Coachella Valley Agricultural Research Station in Thermal, CA and at the Yuma Agricultural Center in Yuma, AZ. The treatments were a split-plot arrangement in a randomized complete block design with four replications. Each plot was 27 meters long and 10 rows wide. The four main experimental treatments (Table 1) included: 1) Summer fallow, commonly used to leach salts; 2) Sudangrass that harvested and residues incorporated at the end of the summer prior to planting crops; 3) Cowpea cover crop incorporated into the soil at the end of the summer; and 4) Cowpea crop that mulched to allow cowpea residue to remain on the soil surface. Each of the four main experimental treatments were subdivided into conventional, ICM (integrated crop management), and organic production. Following summer cover crop production, the fall crop of romaine lettuce (Coachella) or iceberg lettuce (Yuma) will be transplanted (mulch plots) or seeded (incorporated plots) in late September. Following the lettuce harvest, muskmelon was transplanted (mulch plots) or seeded (incorporated plots) into all plots. The cowpea mulch plots was not tilled during the entire crop rotation. The incorporated plots were tilled prior to planting each crop.

Table 1. Cropping Systems for Desert Vegetable Production Field Experiment

Main Sub- Crops Tillage Management
Plot Plot Summer Fall Winter/Spring System System

1 A Fallow Lettuce Muskmelon CT Conventional
B Fallow Lettuce Muskmelon CT ICM
C Fallow Lettuce Muskmelon CT Organic

2 A Sudangrass Lettuce Muskmelon CT Conventional
B Sudangrass Lettuce Muskmelon CT ICM
C Sudangrass Lettuce Muskmelon CT Organic

3 A Cowpea Lettuce Muskmelon CT Conventional
B Cowpea Lettuce Muskmelon CT ICM
C Cowpea Lettuce Muskmelon CT Organic

4 A Cowpea Lettuce Muskmelon NT Conventional
B Cowpea Lettuce Muskmelon NT ICM
C Cowpea Lettuce Muskmelon NT Organic

Lettuce was seeded in elevated-double row beds on 1.07 m centers and thinned at the four-leaf stage or transplanted to approximately 60,000 plants/ha. Melons were planted on single row beds on 2.1 m centers and thinned at the four-leaf stage to 30,000 plants/ha. In the no-till cowpea mulch plots, melons will be transplanted into the lettuce beds on 1.07 m centers at 30,000 plants/ha. In the no-till treatments, lettuce and melons were transplanted using a single-row transplanter that has been modified by B & B No-Till of Laurel Fork, VA (Morse, 1995). Management practices followed those practiced by growers in desert production areas with the organic systems following CCOF rules. To maintain consistency across all crops, sprinklers supplied irrigation until the crop was established; drip irrigation was used for the remainder of the season. Composted manure was used as a fertilizer in organic plots and inorganic fertilizers were used in the conventional production plots. Fertilizer applications were made in the cash crops based upon biweekly petiole analysis.
Data was collected in all crops on pest populations and soil factors. Biweekly measurements of leaf area and mean tip angle were made on the melon and leaf lettuce crops at six locations in each plot with a LiCor 2000 Canopy Analyzer. All pests were sampled as per the UC ICM recommendations for that crop. If disease or insect populations reached their economic injury threshold, the appropriate control measures was taken based on CCOF, ICM, or conventional practices to prevent confounding of experimental results; however, population counts were analyzed for treatment difference.
At two weeks after crop establishment, and every 3 weeks thereafter, weed cover and species composition were assessed from 3 randomly placed 50 by 50 cm quadrats per subplot. Additionally, weed cover and weed seed production were visually assessed for the entire plot. Determinations of the average time taken by hand weeding crews to weed each plot were made. Additionally, soil cores were taken at the end of season and weed seeds germinated in the greenhouse to determine the existent viable weed seed pressure.
At the end of each season, crop nutrient (N,P,K) content were determined by harvesting, drying and grinding aboveground biomass and submitting subsamples to the UC DANR Lab in Davis, CA for analytical determinations. Fifty leaf petioles of the first fully expanded leaf of each crop were sampled four times during each of the four growing seasons and analyzed for tissue N at the UC DANR Lab in Davis using a LECO FP428 Nitrogen Gas Analyzer (St. Joseph, MI). Crop yield and quality were measured at the end of each season by harvesting the central three rows of each plot.
Soil cores were taken randomly from five selected sites in each plot at the end of each of the each season. Soil was sampled at 20 cm increments down to 1 meter below the soil surface. The samples were analyzed for soil e.c., organic matter, and plant available nitrogen. Prior to each summer season, core samples were also analyzed for water stable aggregates to determine the effect of cropping system on soil structure (Amezketa and Singer, 1994). Soil temperature at 15 cm depth were monitored continuously in all treatments using microprocessor controlled temperature data loggers (Onset Computers, Pocasset, MA).
Based on our experimental results and current desert production costs, cost studies will be prepared for the cover cropping systems and a typical conventional farm for each crop. Similar cost studies have been prepared for conventional production of several vegetable crops in the Imperial Valley (Imperial County Coop. Ext. 1995) and organic vegetables in coastal California (Klonsky et al. 1993). These will serve as a basis for our cost studies. The cost studies will utilize commercially available microcomputer spreadsheet software that is familiar to most growers. The cost studies are a valuable, readily trans-ferable software tool which allows growers to plug in their specific costs and determine which alterna-tives could work on their farms. Cost studies will be made available for clientele, University of Califor-nia and University of Arizona personnel, county extension offices, the Vegetable Research and Informa-tion Center, and any other university program requiring the information. Summaries of the cost study comparisons of conventional and cover crop based systems will be included in newsletters, web sites, and other outlets.

Research results and discussion:

Objective 1. Evaluate the effectiveness of cover crops in reduced tillage (surface mulch) and conventional tillage (incorporated) production. The three main treatments are: (1) summer cowpea used as mulch in the fall, (2) summer cowpea incorporated into the soil in the fall, and (3) summer fallow (Figure 1). Each main treatment was subdivided into two sub-treatments (management systems) of either conventional or organic management (Figure 2).

1.a. Improvement of soil temperature regime.
In the low desert, fall vegetable planting may be delayed until high soil temperatures decline to allow seed germination and crop growth. We found that cowpea mulch buffers soil temperature fluctuations (Hutchinson and McGiffen 2000). At a depth of up to 6 inches, cowpea mulch reduced the daily maximum temperature and increased the daily minimum temperature. For fall planted lettuce, decreasing maximum soil temperature may allow growers to plant earlier and therefore target markets with better prices.

1.b. Non chemical weed suppression.
Weed control is a major component of vegetable production inputs in the desert. Weed control is generally conducted manually and therefor constitutes a big constraint to large-scale production. We found that either incorporated into the soil or used as mulch, cowpea cover crop provided better weed suppression than summer fallow or sudangrass cover crop for the fall planted lettuce (Hutchinson and McGiffen 2000; Ngouajio et al In Press). At Coachella, this effect was carried over from fall lettuce to cantaloupe planted in winter/spring. The organic crop management system also resulted in fewer weeds than the conventional system during the cantaloupe growing season at Coachella (Figure 5). The Yuma, AZ site had a low weed population prior to the start of the experiment, and weeds were generally low throughout the study in Yuma.

1.c. Insect population control.
Insect populations were similar whether the plot was previously fallow, grown with cowpea or sudangrass and residues incorporated or grown with cowpea and residues used as mulch. Cover crops do not appear to increase insect populations by serving as an alternative summer host.
The crop management system affected insect populations. The organic system had more leaf feeding insect crop injury than the conventional system. This was probably not due to the inherent ability of organic system to attract insects, but more likely to a reduced activity of insecticides used in organic plots. More effective insect control is an obvious need for organic production.

1.d. Crop growth and yield.
The cowpea cover crop significantly boosted lettuce yield, but the sudangrass cover crop decreased yield (Figure 3). All plant growth characteristics including average lettuce head weight, head diameter, leaf weight, leaf area, dry biomass, and yield were smaller in sudangrass plots. Parallel to the low yield, lettuce plants from sudangrass plots showed low midrib nitrate-N content (Figure 7). This result indicates either nitrate immobilization during the decomposition of sudangrass residues or release of allelochemicals by sudangrass residues, which may interfere with nitrate uptake by the crop. However, effect apparently declined during the lettuce growing season. Cantaloupe planted in the same plots the subsequent spring had the greatest fruit yield in the summer sudangrass plots in Yuma and similar to yield in fallow plots at Coachella. In both sites, sudangrass residues were completely decompose by the end of the lettuce season. Severe cantaloupe yield reduction (40 to 60%) was observed in cowpea mulch plots. Due to rapid decomposition, the beneficial effects of the mulch were eliminated, and soil compaction was readily apparent. Reduced tillage systems may require the use of conventional plowing after each crop.
For all crops and sites, the organic management system resulted in lower crop growth and nitrate content as well as smaller yields when compared to the conventional or the integrated system in the first year (Figure 7). However, the yield penalty was within acceptable limits in Coachella, although significantly less than the conventionally managed plots in Yuma. In the second year, yields for conventional and organic management systems were equivalent when pest populations were below damage thresholds for Coachella. . In Yuma, AZ, lettuce and melon yields were always less for the organic treatments compared to the conventional treatments. For lettuce both insects and soil fertility limited yields in the organic plots. For melons the limiting factor in the organic plots was always insects.

Plant nitrogen content was less stable when no cover crop was planted. Lettuce leaf nitrate content rose dramatically in the summer fallow treatments, declining just before harvest. Leaf nitrate content was relatively stable for either cover crop regime throughout the growing season, especially when cowpea was incorporated prior to lettuce planting. However, leaf nitrate levels were dramatically lower in the bareground (summer fallow) treatments during the critical first month of lettuce growth.
The bareground treatments also had large fluctuations in soil nitrate content. Early season soil nitrate content was tenfold greater in the bareground treatments than either cowpea cover crop treatment (Figure 8). However, soil nitrate reserves declined sharply in the summer fallow treatments throughout the growing season, while soil nitrate levels in lettuce following either cover crop system remained relatively unchanged. As a result, while soil nitrate levels in following summer fallow was greatly lower by the end of the season, soil nitrate content was similar across all cover crop regimes at harvest time.

Objective 2. Develop cost studies for desert ICM and organic based vegetable production systems and compare those costs to conventional production systems.

These studies are currently underway. Preliminary results indicated that the number of handweedings and insecticide applications are smaller in the ICM and organic systems than in the conventional system. These findings will likely guaranty greater net benefit for the ICM system since its yield was comparable to that of the conventional system. Even though yield was slightly reduced in the organic system, low inputs and higher market prices of organic produces may also counterbalance yield penalties.

Objective 3. Extent current knowledge of cover crop systems to vegetable growers, Soil Conservation Service, and other interested parties. We have gotten excellent response to our results, including many requests for talks and papers. The project has led directly to many extended collaborative ventures that follow up our research and extension projects.

Researchers from the University of California Cooperative Extension and USDA have been experimenting with cover crops as a way to maintain soil quality in many cropping situations (Cavanaugh 1998). But vegetable producers plant two or more high value crops per year to recover high land and water costs. It seemed impractical to invest additional land, labor, and other production costs into the uncertain payback of cover crops.
But growers began to experiment. They found a gap between spring and fall plantings when the land was usually fallow (Ngouajio and McGiffen 2000). A cowpea cover crop was inexpensive, required little water and no fertilizer, and produced abundant biomass and nitrogen (Aguiar et al 1998). Cowpea cover-crop acreage went from virtually none in 1997 to over 1,000 hectares in 1999. Some of this increase was driven by the increased demand for organic produce. Many limited resource farmers view organic vegetables as a niche market that allows them to remain competitive (Vischer 1994). Since production costs and market value are generally higher for organic produce, some growers wondered whether the costs of growing organically certified produce was worth the benefit (Brumfield et al 2000). But many farmers also recognized that cover crops offer many advantages in vegetable production, including N fixation, recycling nutrients, reducing soil erosion, and adding organic matter to the soil (Gaskell et al 2000; Stirzaker et al., 1992; Stirzaker et al., 1993). Strong grower interest led to increased breeding and pest management research to develop cover crop cultivars with enhanced resistance to nematodes (Matthews et al 1998), weeds (Hutchinson and McGiffen 2000), and other pests (Hall et al 1997). Because nematode, weed, and other pest populations decline after planting resistant cowpeas, it appears possible that novel cover crop varieties could replace fumigation and other chemical pest control. Cover crop cultivars may eventually be developed to solve specific problems from conventional agriculture, such as the loss of methyl bromide and other pesticides.

Research conclusions:

Researchers from the University of California Cooperative Extension and USDA have been experimenting with cover crops as a way to maintain soil quality in many cropping situations (Cavanaugh 1998). But vegetable producers plant two or more high value crops per year to recover high land and water costs. It seemed impractical to invest additional land, labor, and other production costs into the uncertain payback of cover crops.
But growers began to experiment. They found a gap between spring and fall plantings when the land was usually fallow (Ngouajio and McGiffen 2000). A cowpea cover crop was inexpensive, required little water and no fertilizer, and produced abundant biomass and nitrogen (Aguiar et al 1998). Cowpea cover-crop acreage went from virtually none in 1997 to over 1,000 hectares in 1999. Some of this increase was driven by the increased demand for organic produce. Many limited resource farmers view organic vegetables as a niche market that allows them to remain competitive (Vischer 1994). Since production costs and market value are generally higher for organic produce, some growers wondered whether the costs of growing organically certified produce was worth the benefit (Brumfield et al 2000). But many farmers also recognized that cover crops offer many advantages in vegetable production, including N fixation, recycling nutrients, reducing soil erosion, and adding organic matter to the soil (Gaskell et al 2000; Stirzaker et al., 1992; Stirzaker et al., 1993). Strong grower interest led to increased breeding and pest management research to develop cover crop cultivars with enhanced resistance to nematodes (Matthews et al 1998), weeds (Hutchinson and McGiffen 2000), and other pests (Hall et al 1997). Because nematode, weed, and other pest populations decline after planting resistant cowpeas, it appears possible that novel cover crop varieties could replace fumigation and other chemical pest control. Cover crop cultivars may eventually be developed to solve specific problems from conventional agriculture, such as the loss of methyl bromide and other pesticides.

Participation Summary

Educational & Outreach Activities

Participation Summary

Education/outreach description:

Dissemination of Findings

Organized colloquia at ASHS meetings in Minneapolis, MN in 1999. Proceedings were published as a special issue of HortTechnology (Vol. 10, issue 4); the introduction to the colloquia discusses this W SARE project and its applicability to other locations. Companion articles discuss all aspects of organic production and contrast with conventional methods.
Soil Health Symposium — organized by USDA NRCS and ARS, and the Coachella Valley Water District and RCD. Featured speakers from across the country.
Several newsletter and popular press articles on the project and related concepts.
Seven presentations at Pesticide Applicator Profesional Association (PAPA) and CAPCA conferences as outreach to Pest Control Advisors and agri-industry.
Presentations at the ASHS national meetings, Western Society of Weed Science and California Weed Science Society meetings.
Presentations, reports, Q&A to Cooperative Extension Workgroups.
Progressive Farmers meeting presentation in Blythe,.CA. Coachella Valley Cooperative Extension Newsletter article.
Website with technical information on research results: http://cnas.ucr.edu/~bps/hcoopext.htm
Field day at Yuma Ag Center for the Arizona Vegetable Council.
Aguiar, J.L., W.A. Williams, W.L. Graves, M.E. McGiffen, Jr., J.V. Samons, J.D. Ehlers, and W.C. Matthews, Jr. 2001. Factor for estimating nitrogen content of cowpea as a cover crop. J. Agron. Crop Sci. 186:145 -149.

Ngouajio, M., M.E. McGiffen, Jr., S. Mansfield, E.J. Ogbuchiekwe. 2001. Comparison of methods to estimate weed populations and their performance in yield loss description models. Weed Sci. 49:385-394.

Hutchinson, C.M. and M.E. McGiffen. 2000. Cowpea cover crop for weed control in desert bell pepper production. HortScience – Hutchinson, C.M. and M.E. McGiffen. Cowpea Cover Crop for Weed Control in Desert Bell Pepper Production. HortScience Vol. 35(2):p. 196-198

McGiffen, M.E., Jr., J. Ehlers, J. Aguiar. Introduction. Colloquium on Organic Horticulture. HortTech. 10(4):661-662.

McGiffen, M.E., (ed.). Colloquium on Organic Horticulture. HortTech. 10(4):661-662.

Bell, C.E., S.A. Fennimore, M.E. McGiffen, Jr., W.T. Lanini, D.W. Monks, J.B. Masiunas, A. R. Bonanno, B.H. Zandstra, K. Umeda, W.M. Stahl, R.R. Bellinder, R.D. William, and R.B. McReynolds. My View: The Food Quality Protection Act. 2000. Weed Science 48:1.

Rivas, J. and McGiffen, M.E., Jr. 2000. California Squash Production. PIAP, http://pestdata.ncsu.edu/cropprofiles/docs/casquash.html, 28 pages.

Barbosa, M. and McGiffen, M.E., Jr. 2000. Bell Peppers in California. PIAP, 28 pp.

McGiffen, M.E., Jr., D.W. Cudney. 1999. Pest of the Month: Lambsquarters. American Vegetable Grower June 1999.

McGiffen, M.E., Jr., D.W. Cudney.1999. Pest of the Month: Shepardspurse. American Vegetable Grower September 1999.

McGiffen, M.E., Jr., D.W. Cudney. 2000. Pest of the Month: Black Nightshades. American Vegetable Grower January 2000.

McGiffen, M.E., Jr., D.W. Cudney. 2000. Pest of the Month: Common Cocklebur. American Vegetable Grower May 2000.

McGiffen, M.E., Jr. 2000. Cowpea Cover Crops. Western Farm Press, September 16, 2000.

McGiffen, M.E., Jr., D.W. Cudney. 2000. Pest of the Month: Annual Sowthistle. American Vegetable Grower August 2000.

McGiffen, M.E., Jr., D.W. Cudney. 2001. Pest of the Month: Common Ragweed. American Vegetable Grower April 2001.

McGiffen, M.E., Jr., D.W. Cudney. 2001. Pest of the Month: Velvetleaf. American Vegetable Grower June 2001.

McGiffen, M.E., Jr., D.W. Cudney. 2001. Pest of the Month: Common Mallow. American Vegetable Grower January 2002.

McGiffen, M.E., Jr. and C. Hutchinson. 1999. Coachella Valley Cover Crop Research. Desert Ag-Notes, November 1999.

C.M. Hutchinson, McGiffen, M.E. Jr., J.Aguiar. 1999. Coachella Valley cover crop-weed control trials. KAC Plant Protection Quarterly 9:3-5.

Hutchinson, C. M. and M. E. McGiffen, Jr. 1999. Cowpea cover crop for weed control in vegetable production, Weed Science Society of America Abstracts 39:23-24.

Galadima, A., C.A. Sanchez, J. Palumbo, B. Tickes, M. Matheron, M.E. McGiffen, Jr. 2000. Preliminary evaluation of organic desert vegetable production systems. HortScience 35:393

Mitchell, J.P., E.M. Miyao, M.E. McGiffen, Jr., and M.D. Cahn. 2001. Conservation tillage research and extension education in California. HortSci. 36:472.

Wang, G., J. Ehlers, E. Ogbuchiekwe, and M.E. McGiffen, Jr. 2001. Cowpea cover crop varieties resist weed competition. HortSci. 36:473-474.

Ngouajio, M., M.E. McGiffen, Jr. C.A. Sanchez, and A. Galadima. 2001. Use of compost in desert vegetable production. HortSci. 36:518.

Ngouajio M., M. E. McGiffen, Jr., and C. M. Hutchinson. 2002. Effects of summer cover crop and in-season management system on weed infestation in lettuce. Weed Science (submitted).

Ngouajio M., and M. E. McGiffen, Jr. 2002. Going organic changes weed population dynamics HortTechnol. (submitted).

Hutchinson, C.M. and M.E. McGiffen. 2000. Cowpea cover crop for weed control in desert bell pepper production. HortScience 36:552.

Interview “Desert Vegetables”, Today Show, KYMA Television, Yuma, AZ. November 18, 1999.

Presented talk “Weeds Are Not Pests: Biology of Weeds”. PAPA Seminar, Ontario, CA, March 22, 2000

Presented talk “Desert Weed Control Update” Progressive Farmers Meeting, Blythe, CA, April 20, 2000.
Presented talk “Cowpea Cover Crops Reduce Weed Populations in Peppers”. PAPA Seminar, Holtville, CA, May 11, 2000.
Presented talk “Biology of Weeds” PAPA Seminar, San Diego, CA, July 26, 2000.

Presented talk “Sustainable Desert Agriculture Production”, 1st Soil Health Symposium, La Quinta, CA, October 25, 2000.

Presented Poster, “Reducing weed population and soil temperature in desert vegetable production with cowpea mulch” at the DANR Statewide Conference in Riverside, CA February 23, 2001.

Presented Talk “Is There Really an “Organic Effect”?”, PAPA Seminar, Tulare, CA, May 3, 2001.
Presented Talk “Reduced Tillage in the Low Desert” at the Conservation Tillage Workshop in Five Points, CA, June 26, 2001

Presented Talk “Reduced Tillage in the Low Desert” at the Conservation Tillage Workshop in Davis, CA, June 28, 2001

Organized and moderated the Plant Stress Symposium, Riverside, CA, July 9, 2001.

Presented talk “The Organic Effect in Desert Vegetables, Plant Stress Symposium, Riverside, CA, July 9, 2001.

Presented poster, Cowpea cover crop for weed control in vegetable production, Weed Science Society of America Annual Meeting, February 8, 1999, San Diego, CA.

Member, American Society for Horticultural Science Workgroups: Computer Applications in Horticulture, Weed Control and Pest Management, Vegetable Crop Management. 1998-present.

Presented talk, “Production Systems for Desert Vegetables” as part of Colloquia “Organic Horticulture”, 1999 ASHS International Meeting, July 31, 1999. Minneapolis, MN.

Presented poster “Cowpea Cover Crop Mulch Controls Weeds in Transplanted Bell Peppers” CWSS, Sacramento, CA, January 10-12, 2000.

Presented poster “Cowpea Cover Crop Mulch for Weed Control in Desert Pepper Production” WSWS, Tucson, AZ, March 14-16, 2000.

Presented talk “Cowpea Cover Crop for Vegetable Production”, PAPA Seminar, Oxnard, CA, November 29, 2000.

Presented talk “Organic matter changes soil ecology”, PAPA Seminar, Cathedral City, CA, December 12, 2000.

Presented Poster “Cowpea Cover Crops Reduce Weed Populations And Soil Temperature In The Low Desert” at the conference Partnership for Sustaining California Agriculture, Hedrick Agricultural History Center, Woodland, CA, March 27-28, 2001.

Presented invited talk “Use of compost in desert vegetable production” at the ASHS meetings in Sacramento, CA July 24, 2001.

Presented invited talk “Going organic changes weed population dynamics” at the ASHS meetings in Sacramento, CA July 23, 2001.
Presented poster “Reducing weed population and soil temperature in desert vegetable production with cowpea mulch” at the ASHS meetings in Sacramento, CA July 24, 2001.

McGiffen, M. E., Jr. Feb. 1999. Sustainable desert vegetable production. 1998 AES Annual Progress Report.

M. McGiffen, D. Cudney, E. Ogbuchiekwe, and J. Aguiar. 1999. Weed Management Research and Extension for Vegetable Crops. DANR Weed Science Workgroup. 5 pages.

McGiffen, M.E., Jr., J. Aguiar, W. Graves, E. Ogbuchiekwe, N. Toscano, D. Cudney, M. Stanghellini, P. Roberts, and E. Takele. 1999. Effect of Alternative Cropping Systems on Desert Vegetable Pests. 1998-1999 FY Report, Center for Pest Management Research and Extension, 17 pp.

Project Outcomes

Project outcomes:

These studies are currently underway. Preliminary results indicated that the number of handweedings and insecticide applications are smaller in the ICM and organic systems than in the conventional system. These findings will likely guaranty greater net benefit for the ICM system since its yield was comparable to that of the conventional system. Even though yield was slightly reduced in the organic system, low inputs and higher market prices of organic produces may also counterbalance yield penalties.

Farmer Adoption

Farmer Adoption and Direct Impact
The project has succeeded in at least introducing the concept to growers. We now estimate that there are at least 3000 acres of cowpea cover crops grown in the low desert valleys of Yuma, Imperial and Coachella, with interest growing in other regions as well. Growers and researchers are considering cover crops for many conventional agriculture applications. It is thought that by breeding new cover crop specific varieties with enhanced pest resistance we may create a cultural alternative to methyl bromide and other pesticides.

Reactions from Farmers and Ranchers
Growers routinely look at organic vegetables as potential new crops. The low desert can fill market niches that other regions cannot, and organic vegetable production adds to that advantage. Growers frequently want to know where they can get cowpea cover crop seed, and we have identified and passed along suppliers. They also frequently suggest improvements for new cover crop varieties. They are very interested in developing a local cover crop seed production industry. We received questions on whether composting kills pests and eliminates pesticide residues.

Producer Involvement
There is a core group of about a dozen in Coachella and a similar number in Yuma that are regular attendees at all events and are most interested in our project. A similar number have tested at least some of our ideas. Producer involvement has begun to spread to other parts of Arizona and California, notably the Central Valley. Close links with other Cooperative Extension workers have made this possible, and we freely send information.
We have set up on-farm demonstrations for about ten growers on different aspects of our work. Last year we conducted on farm demonstrations of preplant compost applications. We also worked with a local composter and conducted experiments that verified that composting as per California’s standards kills all pests and does not return weed seed or other pest propagules to grower fields.
Most of the attendees at PAPA, CAPCA, and similar local events are pest control advisors and other professionals that work for farmers and related agri-industry. The ASHS and other professional meetings are dominated by Cooperative Extension and other academics. From the list of events in the above “Dissemination of Findings”, we estimate attendance of 90 growers at events related to this project. The diversity of attendees is especially gratifying, from small to large farmers, and of wide ethnic and other demographic groups.

Recommendations:

Areas needing additional study

We know that using cover crops, reducing tillage, and amending with compost change the agroecosystem. What we do not know is the mechanisms behind the change. Why do weed populations change? What is happening with nitrogen cycling? Are soil physical and microbial parameters changing? Can we develop better cover crop cultivars or combinations of cover crop species?

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.