Cropping Systems for Intensive Desert Vegetable Production.”
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PROJECT REPORT h RESEARCH AND EDUCATION h SARE Final Results SW98-044 Cropping Systems for Intensive Desert Vegetable Production http://wsare.usu.edu Location: OBJECTIVES California and Arizona This project has three goals: Funding Period: Dec. 1998 – Nov. 2001 1. Evaluate the effectiveness of cover crops in reduced-tillage (surface mulch) production and conventional tillage (incorporated) production Grant Award: 2. Develop cost estimates for desert integrated crop management (ICM) and $130,672 organic production systems compared with costs of conventional systems 3. Disseminate information on cover crop systems to vegetable growers, Project Coordinators: agriculture-support agencies and other interested parties Milt McGiffen Vegetable Crops Specialist Department of Botany and ABSTRACT Plant Sciences In the Coachella Valley of California and Yuma, Ariz., both in the major University of California Riverside, CA 92521-0124 vegetable production area of the Lower Colorado River, interest in sustainable (909) 560-0839 production systems is rising among growers. This three-year SARE project [email protected] evaluated the potential for summer cover crops and management systems for intensive desert vegetable production. Charles Sanchez Resident Director Yuma Valley Ag Center Two cover crops, cowpea and sudangrass, were compared with traditional 6425 W. 8th St. summer fallow. The sudangrass was incorporated into the soil, and the cowpea Yuma, AZ 85364 was either incorporated or used as mulch in a reduced-tillage system. Major Participants: University of California Cowpea mulch increased daily minimum soil temperature and decreased the Jose Aguir maximum soil temperature, which may allow growers to extend their seasons Vegetable Crops and Small into more profitable markets. Farm Advisor Jeff Mitchell In the first year, yields for melons and lettuce were lower when managed Vegetable Specialist organically. In Yuma, lettuce and melon yields were always lower in the organic treatments compared with conventional. For lettuce, insects and soil fertility For a list of more major limited yield in organic plots. For melons, the limits were always insects. participants and cooperators, please scroll to the bottom of this report. In the second year, organic yields equaled those under conventional management in Thermal, Calif. Insect populations in Thermal were lower than in Yuma throughout the study. Cowpea cover crops decreased the diversity of weed species but not insect populations, suggesting the cover crops don’t serve as an alternate host for pests. Cowpea, which significantly increased yields of fall-planted lettuce and winter/spring cantaloupe, requires little water, needs no fertilizer, produces abundant biomass and nitrogen and reduces weeds and nematodes. “Incorporating summer cowpea residues into the soil significantly increased yield for both conventional and organic management systems,” says the project’s final report. “Growers have followed up on our results by increasing the acreage planted to cowpea cover crops from nearly zero in 1995 to several thousands and increasing.” Sudangrass as a cover crop increased the yield of cantaloupe but not lettuce. The reduced lettuce yield may have resulted from nutrient immobilization or allelopathy from the crop residue. A reduced-tillage system using cowpea mulch reduced weed populations and provided nutrients to the fall crop. However, because of rapid decomposition in the desert, those benefits were not carried over into the spring cantaloupe crop. 2002 i SW98-044i 1 SPECIFIC RESULTS Objective 1. Three treatments were tested: 1) summer cowpea used as mulch in the fall, 2) summer cowpea incorporated into the soil in the fall and 3) summer fallow. Each treatment was subdivided into conventional and organic. The researchers looked at cover crop effects on soil temperatures, weeds, insects and crop growth and yield. Temperature. In the low desert, planting fall vegetables may be delayed until soil temperatures decline to allow seeds to germinate and crops to grow. To a depth of up to 6 inches, cowpea mulch reduced the daily maximum temperature and increased the daily minimum temperature, which would allow growers to plant earlier and target markets with better prices. Weeds. Weed control in the desert is often done by hand, an expense that can limit large-scale production. Either incorporated into the soil or used as mulch, the cowpea cover crop suppressed weeds better than summer fallow or sudangrass for fall-planted lettuce. At Coachella, the effect was carried over from fall lettuce to cantaloupe planted winter/spring. The system managed organically had fewer weeds than the conventional system during the cantaloupe season at Coachella. The Yuma site, which had a low weed population before the experiment started, had generally low weed counts throughout the study. Insects. Insect populations were similar for all fallow and cover crop treatments, suggesting that cover crops do not increase insect populations by serving as a host. However, the crop management system did affect insects. The organic system had more injury from leaf-feeding insects than did the conventional system, in part because of the inherent ability of the organic system to attract insects, but more likely the reduction in insecticides. More effective insect control is an obvious need in organic production. Crop growth and yield. The cowpea cover crop boosted lettuce yield, but the sudangrass cover crop reduced yield. In addition to smaller weight, head diameter, leaf weight, leaf area, dry biomass and yield, lettuce in the sudangrass plots had low midrib nitrate-N content. Either the nitrates were immobilized during the decomposition of the sudangrass or a release of allelochemicals interfered with nitrated uptake. Whatever the effect, it apparently declined during the lettuce-growing season as cantaloupe planted in the same plots the next spring had the greatest fruit yield in the summer sudangrass plots in Yuma and yields similar to the fallow plots at Coachella. In both sites, the sudangrass was completely decomposed by the end of the lettuce season. Meanwhile, cantaloupe yield was reduced severely (40-60%) in cowpea mulch plots, where rapid decomposition eliminated any benefits and the soil became compacted. In this case, reduced tillage may require conventional plowing after each crop. For all crop sites, the organic management system resulted in lower crop growth, nitrate content and yield compared with the conventional in the first year. The yield penalty was within acceptable limits in Coachella. In the second year, yields for conventional and organic were similar at Coachella when pest populations were below thresholds. In Yuma, lettuce and melon yields were always less for organic than for conventional, with insects and soil fertility limiting lettuce and insects limiting melons. Objective 2. Cost studies for desert integrated crop management (ICM), organic and conventional systems are currently being done. Preliminary results indicate that fewer hand weeding and insecticide applications are required under ICM and organic, findings likely to guarantee greater net benefit for ICM given that its yield is comparable with the conventional. Even though yield is slightly reduced in the organic system, lower inputs and higher prices for organic products could counterbalance yield penalties. Objective 3. The project and its results have generated wide interest, as evidenced by many request for talks and papers on the subject. In addition, the project has led to many extended collaborative ventures that are following up this research. Project members have presented results at numerous seminars, workshops and field days, had their findings published in technical journals (HortScience and Weed Science, to name two) and had several articles published in popular farm magazines like American Vegetable Grower. 2002 i SW98-044i 2 POTENTIAL BENEFITS Before the project, few desert vegetable growers used cover crops, thinking such crops needed more water and would not fit production systems. However, with the increased interest in organic produce as a niche crop that can sustain profitability, many conventional growers are adopting cover crops and other methods developed by this project. FARMER ADOPTION AND DIRECT IMPACT The project has succeeded at introducing the cover crop concept. Estimates show at least 3,000 acres of cowpeas being grown in the low-desert valleys of Yuma, Imperial and Coachella, with interest growing in other areas. Breeding new cover crops with enhanced pest resistance may create a cultural alternative to methyl bromide and other pesticides. Many growers have inquired about sources of cowpea cover crop seed and have suggested improvements for new cover crop varieties. They also like the idea of developing a local cover crop seed industry. “We have certainly changed the way producers look at things,” says Milt McGiffen, project coordinator. “We have provided them with new tools that are being used on thousands of acres in the original target area of the low desert and in places far away.” FUTURE RECOMMENDATIONS OR NEW HYPOTHESES While the project results strongly support the use of cowpea cover crops before fall-planted lettuce in the desert, the research team suggests that more investigation is needed on the benefits of sudangrass as a cover crop before lettuce. The research team has suggested that Western SARE develop generic tools that each funded project could use to build a Web site that could