Location: Crop Improvement and Protection Research
2023 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
This is the final report for this project that is undergoing NP 216 OSQR review; the new project will be established in fiscal year 2024.
During the past five years, this project has focused primarily on long-term systems research using the ongoing Salinas Organic Cropping System (SOCS) experiment that investigates crop rotations, soil fertility, weeds, and the effects of organic matter inputs from cover crops and compost in high-value organic vegetable and strawberry systems. The SOCS experiment is currently in its 20th year and is the longest running systems experiment in the United States that is focused on high-value, high-input organic crop production. The project also includes important short term (two to three year) studies that complement the long-term research. The research in this project occurred on certified organic land at the ARS and on collaborating farms and is applicable to small, medium and large-scale organic farms. The research is also applicable to conventional farms that are shifting to more sustainable, climate-smart soil management practices. This research involved collaboration on multidisciplinary projects with farms in the Salinas Valley region of the central coast of California and with scientific and extension personnel from other agencies. All of the work relates to the project objective, which is to 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.
Substantial results were realized from the long-term systems research component of this project including the following: 1) Data was collected on cover crop biomass yields, disease, and soil changes during years 15 to 20 of the SOCS experiment. 2) Soil carbon data collected during the intensive vegetable production phase (years 1 to 8) was used to evaluate the effects of cover crop type (rye, legume-rye mixture, mustard), cover cropping frequency (annually versus every 4 winters), and yard-waste compost on soil carbon stocks. This showed that carbon inputs from cover crops increased the readily decomposable carbon fraction, but that total carbon stocks were driven primarily by compost inputs. 3) Data from year 1 to 8 of the long-term trial were used to develop detailed nitrogen budgets for five intensive organic vegetable rotations that differed in cover crops and compost inputs. These nitrogen budgets revealed that compost inputs increased total nitrogen stocks but had relatively little effect on vegetable nitrogen uptake or yields, whereas cover cropping increased vegetable nitrogen uptake and yields. Overall, this suggested that the increased use of annually planted nonlegume cover crops can improve efficient nitrogen (N) use and cropping system yield, consequently improving environmental performance. The nitrogen budgets also showed that less than 25 percent (%) of the applied nitrogen in the five systems evaluated was exported in harvested product, and this raises important questions about large potential nitrogen losses from tillage-intensive, high-input vegetable production systems. 4) Through research, ARS scientists in Salinas, California, discovered that a foliage-feeding, migratory bird (White Crowned Sparrow) preferentially feeds on mustard cover crop biomass. This information may help farmers reduce damage on lettuce and broccoli by using mustard cover crops to attract migratory sparrows away from these vegetables. 5) Cover crop biomass data from the SOCS experiment was used to justify an approximately three-fold increase in the cover crop nitrogen scavenging credits in the California regulation known as Ag. Order 4.0, which is a new and important nutrient management regulation affecting 540,000 acres of land in the central coast region. This improvement in this game-changing regulation highlights the value and impact of long-term research to improve nutrient management and ground water protection in a region of the country that provides high-value vegetables for entire United States and beyond. This unique long-term research approach is generating much more robust scientific information than would be produced from the more typical short-term (i.e. 2 year) studies. Overall, these findings highlight the need for both organic and conventional vegetable farms in the central coast of California to maximize their use of cover crops in these high-input systems to improve their sustainability and reduce their impact on ground water and climate change.
The short-term research in this project was focused on developing several novel tools and methods to help farmers with interplanting plants that favor beneficial insects in vegetable systems, soil erosion/runoff control in strawberry furrows, and cover crop nitrogen scavenging credits. This research provided useful and novel tools to improve the sustainability of these systems. For example, a novel and efficient planter called the Slide Hammer Seeder was developed for precision planting of small-seeded herbs, vegetables, and other species with extremely small seeds that are the size of a grain of salt and can be difficult to plant with standard planters. The planter has been used to efficiently sow sweet alyssum plant seed between vegetables to improve biological control of aphids in lettuce. Another novel tool developed during the past 5 years was a cover crop mower for controlling cover crop growth in strawberry furrows. Cover cropping in strawberry furrows is important to increase infiltration of rainfall and thus reduce soil erosion and runoff. This mower helps farmers to manage furrow cover crops with less labor and will likely increase the adoption of cover cropping in the Central Coast region of California. Models were also developed to help farmers reliably predict cereal cover crop shoot biomass using length of the cover crop’s main stem. This method has been accepted by the Central Coast Regional Water Quality Control Board as a way for farmers to estimate cover crop biomass so that they can maximize their cover crop nitrogen scavenging credits as part of the Ag. Order 4.0 regulation.
The project had several impactful technology transfer accomplishments during the past five years, and these helped to efficiently communicate the research results to stakeholders. This involved producing several engaging and informative YouTube videos. These videos have been used in numerous university classes and farmer meetings. The videos have received over 260,000 views during the project period. The research videos focused on long-term systems research, cover cropping in strawberry furrows (in English and Spanish), and methods to help farmers get cover crop nitrogen scavenging credits. In addition, several tutorial videos were produced to inspire and train scientists to make YouTube videos for effective science communication.
Accomplishments
1. Outreach videos to help farmers get nitrogen scavenging credits for winter cover cropping. In 2023, a new California regulation takes effect that limits the amount of nitrogen fertilizers that can be applied to irrigated land in the Central Coast Region. Winter cover crops that absorb leftover nitrogen fertilizers is a best management, climate-smart strategy that can help farmers comply with this regulation. An ARS researcher in Salinas, California, produced two YouTube videos that provide important information on how farmers can get cover cropping credits. These farmer-friendly videos were based on research at the ARS and are helping to incentivize cover crops, improve nutrient management, and protect surface and groundwater in this region that is known as the ‘Salad Bowl of America’.
