Cover cropping communities of practice in California’s Salad Bowl: Addressing water scarcity and quality to promote
multiple ecosystem services
Hannah Waterhouse, UCSC and Timothy Bowles, UC Berkeley
Background context
California’s agricultural communities face the dual challenges of increasingly variable and limited irrigation water supplies, alongside persistent groundwater quality degradation from nitrate leaching that has imperiled drinking water for nearly one million residents predominantly in rural, LatinX/@ communities throughout the state. In California’s Central Coast, often known as the country’s “Salad Bowl,” intensive vegetable and berry production has led to nitrates from fertilizers ending up in groundwater. Drinking nitrate contaminated water has been associated with blue-baby syndrome, hypertension, and some cancers. Planting winter cover crops, crops not intended for harvest but rather planted between cash crop cycles to keep the soil healthy, can help prevent residual nitrate left over from the growing season from reaching surface and groundwater bodies during the period when this region receives most of its rainfall. However, cover crop adoption is low — as little as five percent of the farmland in this region goes to cover cropping. One barrier to cover cropping is the perception that they consume too much water and leave little water stored in the soil for cash crop establishment. While cover crops do indeed transpire, they also provide many potential benefits to bolstering water resources, including increasing infiltration and reducing subsequent runoff and erosion, increasing organic matter and accompanying increases in water storage, and reducing evaporative losses from bare soil. Through both controlled trials at the UCSC Farm (“parent trial”) and on-farm, participatory research (“baby trials”), we aim to determine how different cover crop management practices affect the balance between water regulation and provisioning and water quality protection, as well as the supply of nitrogen (N) for cash crops.
The “parent trial” includes a fallow treatment, an October planted rye cover crop treatment (representing the recent Agricultural Order 4.0 incentive requirements for cover cropping), a rye/vetch October planted treatment, a November planted rye treatment, and a November planted rye/vetch treatment. We will measure plot level evapotranspiration, soil moisture content over time, plant biomass and nitrogen content at the end of the cover crop period, and ammonium and nitrate concentrations over time down to 90cm during the cover cropped period, as well as between cover crop termination and cash crop planting.
In partnership with technical assistance providers, Aysha Peterson and Sacha Lozano from the Resource Conservation Districts (RCD) of Monterey and Santa Cruz counties, respectively, we have recruited 27 farmers to participate in the “baby trials”. Recently, we met with each farmer to discuss the trial and get their input and consent for the soil sampling plan. Farmers choose from one of four cover crop treatments described above, and include a small portion of their field to be left fallow, and have been provided the seed at no cost. We are just beginning the baseline measurements across the farms. We will be measuring soil moisture, ammonium and nitrate, and plant biomass and N content.
Further, we are groundtruthing remotely sensed cover crop data with plot level ET and N content in plant biomass in conjunction with engineering students at UCSC and a graduate student, Kangogo Sogomo at UC Berkeley to expand this project beyond the field scale to regional scales.
The study will be conducted for 3 years at the UCSC Farm and for two years with participating farmers. Each year we will have a knowledge exchange workshop with the RCD’s technical assistance providers, the participating farmers, and the researchers to understand the challenges and successes of cover cropping, and what parameters are acting as barriers or facilitators of this practice. The knowledge exchange process will be formally documented and studied to better understand transitions to agroecological practices. This work will be led by PhD student, Greta Wong, and co-lead by Hannah Waterhouse, Aysha Peterson, Sacha Lozano, Kase Wheatley and Jan Perez.
Timeline and Objectives
2024-2025
- Conducted first “parent trial” at the UCSC farm from October 2024 to March 2025
- Held a “Feria de Recursos” March 2025 to meet potential participating farmers and to provide information on funding opportunities for predominantly spanish speaking farmers
2025-2026
- Hired a postdoctoral scholar to help lead work
- Successfully recruited 27 participating farmers to the “baby trials”
- Conducted management surveys of participating farmers management
- Established second year of “parent trial” at UCSC farm
- Presentation at the California Association of Resource Conservation District November 19th on participatory research
- Soil, plant, and climatic variable sampling is ongoing
- March 2026: 1st knowledge exchange workshop
2026-2027
- Continue both “parent” and “baby” trials
- March 2027: 2nd knowledge exchange workshop
Policy Implications
This project is directly in conversation with the Agricultural Order 4.0 - the Central Coast’s policy on regulating nitrogen discharge from agricultural lands to protect drinking water quality. The treatments were designed to reflect the Agricultural Order’s cover cropping incentive and test other treatments to possibly be incorporated into future orders. This will have implications beyond just the Central Coast’s Irrigated Lands Regulatory Program including the Central Valley as they develop out their regulation further.
Educational Integration
Three graduate students (Miguel Ochoa, Kangogo Sogomo, and Greta Wong), 1 postdoctoral scholar (Mohammad Rahmat Ullah), 1 Jr. Research Specialist (Jorge Gomez-Ortega) and five undergraduate research assistants (Mikayla Butts, Marco Nuńez, Mazzy Jones, Ava Liu, and Kate Heppell) are participating in the project.
Supporting Equitable Agroecological Transitions
Nitrate contamination of drinking water is an environmental injustice impacting predominantly rural, farm working, LatinX communities, and agriculture is the main contributor of nitrates in groundwater. This research will provide information to regulators on how to expand the ability to protect drinking water quality by increasing the adoption of cover cropping practices. We are also working with a cohort of predominantly Spanish speaking, lower-resourced farmers on the Central Coast to help provide technical assistance with soil health practices, including cover cropping, and to support a community of practice in overcoming challenges of cover cropping.