Location: Crop Improvement and Protection Research2020 Annual Report
The long-term objective of this project is to help farmers economically integrate cover crops into tillage-intensive vegetable and strawberry production systems, maximize the benefits from cover cropping, and reduce production costs. This experiment will produce knowledge of short-term (1-2 years) and longer-term (>5 years) effects of cover crops and compost on yield and profitability, soil quality, and pest management, and will be used to make recommendations of optimal rotations. Organic and conventional farmers in California and elsewhere who use cover crops in high-value vegetable and strawberry cropping systems will benefit directly from the results of this research. The research will occur on the USDA-ARS Salinas certified organic research farm in collaboration with local organic farmer cooperators. This research applies to organic and conventional farms that are working to develop more efficient and climate-smart soil management strategies for high-value horticultural crops. Objective 1: Develop ecologically-based soil management strategies for organic vegetable and strawberry production systems that enhance soil quality, nutrient cycling, pest and disease management, profitability, and reduce off-farm inputs. Subobjective 1A: Evaluate the effects of cover cropping frequency and compost on soil quality, vegetable and strawberry yields, and system profitability. Subobjective 1B: Evaluate the effects of a legume-rye mixture versus non-legume cover crops on vegetable and strawberry yields. Subobjective 1C: Evaluate the effects of cover crop seeding rates on weed densities and weed management costs in subsequent vegetable and strawberry crops grown in rotational sequences. Subobjective 1D. Evaluate the effects of cover crop type and seeding rate on soil water storage during winter cover cropping. Subobjective 1E. Evaluate the effects of legume-rye cover crop seeding rate on legume component biomass production.
Subobj. 1.A. Hypotheses. 1.A.1 -Soil quality will be higher in systems where cover crops are used annually than in systems where they are used only quadrennially. 1.A.2 -Soil quality will be higher in systems that receive compost annually than systems that only receive cover crops. 1.A.3 - Vegetable and strawberry yields will be higher in systems where cover crops are used annually than in systems where they are used only quadrennially. 1.A.4 -Vegetable and strawberry yields will be higher in systems that receive compost annually than systems that only receive cover crops. 1.A.5 -Profits will be higher in systems where cover crops are used annually than in systems where they are used only quadrennially. 1.A.6 -Profits will be higher in systems that receive compost annually than systems that only receive cover crops. Subobj. 1. B. Hypothesis 1. B -Vegetable and strawberry yields will be higher following legume versus non-legume cover crops. Subobj. 1.C. Hypotheses. 1.C.1 -Weed density will be lower in vegetable and strawberry systems where cover crops were planted at relatively high seeding rates over several years, than when using lower seeding rates. 1.C.2 -Weed management cost during vegetable and strawberry production will be lower in rotations where cover crops were planted at relatively high seeding rates over several years, than when using lower seeding rates. Subobj. 1.D. Hypothesis. 1.D1 -Planting cover crops at higher seeding rates will reduce soil moisture early in the winter relative to cover crops planted at lower seeding rates, but over time these differences will decline as cover crop shoot biomass differences dissipate. Subobj. 1.E. Hypothesis. 1.E.1 -Planting cover crops at higher seeding rates will increase competition relative to those planted at lower seeding rates, and will alter biomass production of the various legume components. Experimental approach: These subobjectives will be addressed in the Salinas Organic Cropping Systems experiment that began in 2003 and is the longest running trial in the U.S. focused on high-value, tillage intensive organic production systems. It includes 8 systems that for the first 8 years differed in cover cropping frequency, cover crop type, cover crop seeding rate, and compost rate. The experiment has 2 phases: the “intensive phase” for the 1st 8 years when management differed between systems, and the subsequent, and current “legacy phase” that monitors residual effects from the intensive phase. Commercial scale vegetable production was the focus during the intensive phase whereas vegetables and strawberries are grown during the legacy phase. Data is collected on weeds, soil health, cash crop yields, cover crop services, and economics. The results of analysis from the first 15 years of the trial may indicate that there would be value in collecting additional field data during the remainder of the legacy phase or conducting additional analyses of archived soil samples. If this occurs we will modify our plan to collect this additional data with our existing collaborators or seek additional collaborations as needed.
Most of the research effort this fiscal year was focused on Sub-objective 1A, to evaluate the effects of cover cropping frequency and compost on soil quality, vegetable and strawberry yields, and system profitability. This occurred within the Salinas Organic Cropping Systems (SOCS) experiment that is currently in its 17th year on USDA-ARS certified organic land, and is the longest running systems experiment in the United States focused on high-value, high-input organic crop production. The study addresses the needs of small, medium and large-scale organic and conventional farms that are shifting to more sustainable soil management practices. It continues to investigate crop rotations, soil fertility management, weed management, and the effects of organic matter inputs from cover crops and compost in high-value organic vegetable and strawberry systems. We evaluated changes in soil organic matter and nitrogen budgets (inputs from fertilizer, compost and nitrogen fixation versus outputs in harvested product) in this long-term study. The information on nitrogen budgets in this long-term study was used to provide input to the California Central Coast Water Board regulations on waste discharge from irrigated lands. Winter rainfall can cause major problems with runoff and soil erosion in strawberry fields in the Central Coast region of California where most of the soil surface in strawberry fields is covered in plastic mulch. We continued to develop and evaluate novel tools and strategies to help farmers reduce these problems by planting winter cover crops in strawberry furrows. These cover crops helped to increase infiltration of rainfall into the soil surface and thus reduce erosion and runoff. During the past year, a prototype of a novel cover crop mower was developed and evaluated on a collaborating strawberry farm. The preliminary results are promising and indicate that this mower has the potential to help farmers manage furrow cover crops with less labor input and increase the adoption of furrow cover cropping in the Central Coast of California, which could greatly improve the sustainability of strawberry production systems.
1. Cover crops and compost increase soil organic matter in long-term vegetable rotations. Soil organic matter often declines in tillage-intensive vegetable production systems, which can reduce soil health and productivity. Farmers working to improve soil management strategies need long-term information on how organic matter inputs from compost and cover crops affect soil organic matter levels. ARS researchers in Salinas, California, and Beltsville, Maryland, evaluated changes in soil organic matter in several vegetable rotations in the Salinas Valley that differed in the amount of organic matter input from winter cover crops and yard-waste compost over eight years. Although compost and cover crops increased soil organic matter levels, frequent cover cropping had a greater impact on the type of organic matter that is more closely linked to increased crop yields and nutrient cycling. These results highlight the need for innovative strategies to help vegetable farmers in this region to increase winter cover cropping.
White, K.E., Brennan, E.B., Cavigelli, M.A., Smith, R.F. 2020. Winter cover crops increase readily decomposable soil carbon, but compost drives total soil carbon during eight years of intensive, organic vegetable production in California. PLoS One. 15(2). https://doi.org/10.1371/journal.pone.0228677.