PCC July-August 2020

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By planting time, the cover crop residue has already decomposed. This method reduces runoff and erosion but does not reduce nitrate leaching, so this is best for fields with runoff problems but without high nitrate levels. However, this method makes controlling weeds during a wet winter difficult and costs more than simply leaving the field bare (Brennan, 2017.) COVER CROPS IN CALIFORNIA AGRICULTURE: AN OVERVIEW OF CURRENT RESEARCH By SHULAMIT SHRODER | Community Education Specialist, UCCE Kern County Almond Orchard Cover Crop study in Kern County, March 2019 (photo by S. Shroder.) Growers throughout the country and around the world plant a wide range of cover crops for a variety of reasons. Cover crops can reduce soil compaction, improve water infiltration, improve soil structure, and feed soil microbes: they encourage a healthier and more diverse soil ecosystem. Researchers in California are analyzing the best ways to incorporate cover cropping into the state’s diverse agricultural systems, from high-value vegetable production on the central coast to the cotton, tomato, and almond fields of the central valley. Cover Crops on the Central Coast Researchers working with central coast vegetable growers have devised innovative ways to use cover crops to reduce nitrate leaching and agricultural runoff, thereby improving both local ecosystems and soil health. Eric Brennan and his team at the USDA Agricultural Research Service started the Salinas Organic Cropping Systems trial in the Salinas Valley in 2003 to understand the long-term impacts of various cropping systems and soil amendments. This trial focuses on organic lettuce and broccoli, two of the high-value crops grown in the area known as the nation’s salad bowl. To maintain soil organic matter and provide nutrients to their crops, organic vegetable growers in this area prefer applying compost instead of planting cover crops. The amount of time that cover crops require for incorporation and decomposition can shorten the growing season for these high-value crops (Brennan & Boyd, 2012.) To make this practice more feasible for growers in the area, this group of researchers has developed three strategies for integrating cover crops into the vegetable cropping systems of the Central Coast. Option 1: Plant the cover crops only in furrow bottoms, not the entire field. After 50 to 60 days of growth, the grower can spray the cover crops and then do the usual tillage necessary to prepare the ground for planting the cash crops. Option 2: Plant non-legume cover crops on the vegetable beds and mow the cover crops repeatedly throughout the growing season. This maximizes nitrate scavenging while minimizing the amount of residue that needs to decompose right before planting. The ideal cover crop for this practice would be a grass, like cereal rye. Repeated mowing would reduce the amount of water lost to evapotranspiration from the cover crop but still enable the rye to scavenge nutrients that could otherwise be lost to leaching (Brennan, 2017.) Option 3: Turn the cover crop residues into a highly nutritious juice and compost. To do this practice, a grower would plant a non-leguminous cover crop in October and allow it to grow until mid-December, at which point it will have scavenged most of the nitrogen that it will use. The grower then harvests the cover crop, leaving as little residue behind as possible. They can then feed the residue into a screw press, which will separate the liquids and solids. The liquid component has a relatively low nitrogen concentration and can be applied to the vegetable crop to fulfill some of the crop’s nutrient needs. The solid residues can be composted and applied at a convenient time, to provide organic matter to the soil (Brennan, 2017.) Researchers are still working on refining these strategies, but they could allow central coast vegetable growers to reap the rewards associated with cover crops while maintaining a profitable enterprise. Annual Systems in the Central Valley For the past 20 years, Jeff Mitchell and his team at UC Cooperative Extension have studied the effects of reduced tillage and cover crops on a tomato-cotton rotation at the UC’s West Side Research and Extension Center. This study mea- Continued on Page 28 26 Progressive Crop Consultant July / August 2020
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