Cover Crop Use in Vegetable Production
in the Southern California Deserts

Chad Hutchinson and Milt McGiffen

Botany & Plant Sciences Department, UC Riverside

 

Introduction

Desert vegetable growers have become increasingly interested in sustainable production systems. Many are attracted by the higher market price commanded by organic produce. Environmental concerns and an interest in enriching the soil have encouraged others to consider incorporating cover crops and related methods into conventional production systems. Cover crops have been used successfully in other crop production areas as both an incorporated green manure and as a soil surface mulch for weed control. Desert areas offer unique opportunities for production of heat-tolerant cover crops during the summer before the fall/winter crops are planted.

Project 1. Cowpea Cover Crop Mulch for Weed Control in Desert Pepper Production

A two-year field project was conducted in Thermal, CA to investigate cowpea (Vigna unguiculata) mulch as an alternative weed control option in pepper (Capsicum annuum) production. Treatments included: a bare ground production system (BG) with hand weeding, BG with no weeding, a cowpea mulch production system (CM) with hand weeding, and CM with no weeding. Cowpea was seeded in July in 76-cm beds and irrigated with buried drip line. Two weeks prior to transplanting the peppers, irrigation water was turned off to desiccate the cowpea plants. In September, cowpea was cut at the soil-line and mulch returned to the bed top. Pepper plants were transplanted into mulch and fertilized through the drip line. Every two weeks, the number of weeds emerged and pepper plant height were measured. Fruit production, pepper plant dry weight, and weed dry weight were measured at harvest in December.

Fewer weeds emerged in CM compared to BG. The final weed population in non-weeded CM was reduced 80 and 90% compared to non-weeded BG for 1997 and 1998, respectively. Weed dry weights in non-weeded CM were 67 and 90% less than weed dry weights in non-weeded BG, respectively, over the same period. In 1997 and 1998, respectively, pepper plants in CM produced 202 and 156% more dry weight than in BG. Pepper plants in CM produced more fruit weight than in BG with similar fruit size. Cowpea mulch provided season long weed control without herbicides while promoting plant growth and fruit production.

Project 2. Cropping Systems for Intensive Desert Vegetable Production

A multidisciplinary team of research and extension personnel from the Universities of Arizona and California has been working with growers to develop organic and other sustainable production systems for the low desert. A proposal was prepared with input from grower meetings in the Coachella, Imperial, and Colorado River Valleys to investigate whether cover crops can be used effectively in desert vegetable production systems. We proposed a multi-year field experiment in California and Arizona to compare rotations of sudangrass and cowpea cover crops combined with conventional, ICM, and organic vegetable production systems. Crop rotations include planting sundangrass and cowpea cover crops in the summer. Sudangrass will be harvested and the residue incorporated before fall vegetable planting. The two cowpea treatments include incorporated summer-grown cowpea as a green manure and cowpea left on the soil surface as a weed control mulch. In addition, a bare-ground/conventional tillage system has been included for comparison. Lettuce will be planted in all plots in September. Cantaloupe will be planted in all plots in February. The objectives of the proposal are to:

1. evaluate the effectiveness of:
    a) organic mulches at providing non-chemical weed suppression, optimizing soil temperature regimes, and moderating soil moisture loss in surface mulch systems;
    b) cover crops at improving soil organic matter, soil structure, and soil fertility in conventional tillage systems;

2. develop cost studies for desert ICM and organic based vegetable production systems; and,

3. disseminate information through intensive contact with the Progressive Farmer groups in the low desert (who will also supply input on how to adapt our findings to working farms), and through newsletters, meetings, and websites of organizations interested in sustainable agriculture. Frequent field days and grower meetings will ensure rapid adoption of findings and adaptation of future research projects to better meet grower needs. A website (http://cnas.ucr.edu/~bps/hcoopextcrop.html) has been set up to report progress on the project.

The results of our field experiments will be used to derive cost studies that compare the costs and net benefits of conventional, organic, and other production methods. Cost comparisons will be prepared for all production systems to aid growers, lending institutions, and others in comparing potential benefits. This proposal integrates several scientific disciplines to produce research results requested by growers, rapidly disseminate the results, and encourage frequent grower input to direct research and extension programs.

 

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