Location: Crop Improvement and Protection Research
2022 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
The research efforts this fiscal year were focused on the following three main areas:
The Salinas Organic Cropping Systems (SOCS) experiment is currently in its nineteenth 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. The long-term study 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. This fiscal year was focused primarily on Sub-objective 1A, to evaluate the effects of cover cropping frequency and compost on soil quality, vegetable and strawberry yields, and system profitability. Data on nitrogen budgets (inputs from fertilizer, compost, nitrogen fixation and irrigation water versus outputs in harvested product) during the first eight years of this long-term study were published in a peer-reviewed journal. This publication provides the most detailed information on nitrogen dynamics in high-value, high-input vegetable production systems in the Central Coast region of California and revealed that several times more nitrogen was added in the systems than was removed in the harvested products.
In response to the newly adopted regulation known as Ag. Order 4.0, local stakeholder requested information to help farmers know when non-legume cover crops are eligible to meet the regulatory requirements (in terms of biomass quantity and quality) to receive a nitrogen scavenging credit. To address this, five planting date trials with Merced rye and Pacheco triticale were conducted at the ARS with collaborators from the University of California Cooperative Extension. These studies involved sampling cover crops for shoot biomass production and nitrogen and carbon content, shoot height and developmental growth stage from October to April. This intensive study was the primary focus of the project this year and provided critical information that was integrated into the new regulation that takes effect in 2023. The results indicated that growers can reliably use cover crop shoot height to estimate cover crop biomass, and Feekes growth stage to estimate a cover crop’s carbon to nitrogen ratio. These data were integrated into online tools to help growers calculate their cover crop’s nitrogen scavenging credit. This information was provided to the California Central Coast Water Board that is part of the California Environmental Protection Agency that oversees this new regulation that affects nitrogen management and water quality on 540,000 acres of irrigated land in the Central Coast region of California.
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. We also compared the growth of two mustard varieties in strawberry furrows. The results indicate that this ARS-designed 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. Visual methods for farmers to get nitrogen scavenging credits for cover cropping. A new California regulation limits the amount of nitrogen fertilizer that can be applied to irrigated land in the Central Coast region of California that is known as the ‘Salad Bowl of America.’ Growing winter cover crops like rye and triticale is a climate-smart, best-management practice that can improve nitrogen use efficiency and reduce nitrogen leaching into ground water for organic and conventional farms. An ARS researcher in Salinas, California, led a collaborative study to determine simple, visual methods for farmers to know when their cover crops have met the regulatory requirements and are eligible to receive a nitrogen scavenging credit. The critical information from the study was incorporated into this new regulation that will help to incentivize cover cropping on 540,000 acres of irrigated land in the region and protect ground and surface water quality.
Review Publications
White, K.E., Brennan, E.B., Cavigelli, M.A., Smith, R.F. 2022. Winter cover crops increased nitrogen availability and efficient use during eight years of intensive organic vegetable production. PLoS ONE. 17(4). Article e0267757. https://doi.org/10.1371/journal.pone.0267757.
Brennan, E.B. 2021. Using video to give more effective and engaging science talks. Frontiers in Communication. 6. Article 725811. https://doi.org/10.3389/fcomm.2021.725811.
