Location: Crop Improvement and Protection Research
2021 Annual Report
Objectives
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.
Approach
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.
Progress Report
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 18th year on 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. Data on nitrogen budgets (inputs from fertilizer, compost and nitrogen fixation versus outputs in harvested product) in this long-term study were analyzed. Data from this project on cover crop carbon to nitrogen ratios demonstrated that higher nitrogen credits for cover cropping were justified in a regulation (known as Ag Order 4.0) adopted by the California Central Coast Water Board. This regulation impacts 540,000 acres of irrigated land in the Central Coast of California and is focused on protecting water quality.
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, the project continued to evaluate an ARS prototype of a novel cover crop mower that was developed on a collaborating strawberry farm. The results are promising and indicate that this mower has the potential to help farmers manage furrow cover crops with reduced labor input and also increase the adoption of furrow cover cropping in the Central Coast of California, which could greatly improve the sustainability of strawberry production systems.
Accomplishments
1. Long-term research increases nitrogen credits that farmers receive for growing cover crops. Winter cover cropping is a best-management practice to reduce nitrogen leaching into ground water in high-input vegetable systems, but only about five percent of irrigated land in the Central Coast region of California is cover cropped during the winter. To address the issue of ground water pollution from agriculture, a new regulation, known as Ag Order 4.0, was adopted in the Central Coast region of California. Prior to adoption, an ARS researcher in Salinas, California, used long-term cover cropping data to justify increasing the nitrogen credit that farmers receive when they grow winter cover crops. This change improved the regulation and was a positive outcome for farmers and the environment, and it will greatly incentivize cover cropping on 540,000 acres of irrigated land in this important vegetable production region of California.
Review Publications
White, K.E., Brennan, E.B., Cavigelli, M.A. 2020. Soil carbon and nitrogen data during eight years of cover crop and compost treatments in organic vegetable production. Data in Brief. 33. Article 106481. https://doi.org/10.1016/j.dib.2020.106481.
Brennan, E.B. 2020. Sparrow preferences for winter cover crops in California's central coast. Frontiers in Sustainable Food Systems. 4. Article 567579. https://doi.org/10.3389/fsufs.2020.567579.
Brennan, E.B. 2021. Why should scientists be on YouTube? It’s all about bamboo, oil and ice cream. Frontiers in Communication. 6. Article 586297. https://doi.org/10.3389/fcomm.2021.586297.
