CDFA Healthy Soils Week (December 2 – 6 2024) – “A Circular Economy for Healthy Soils”
Each year, the California Department of Food and Agriculture hosts Healthy Soils Week to spotlight the state’s sustainable farming efforts. This year’s theme, “A Circular Economy for Healthy Soils,” connects soil health to our food system, water supply, climate resilience, and economy.
Sustainable Conservation’s Solutions in our Soil program sits comfortably at the intersection of soil health and water. We recognize that healthy soil is foundational to California’s water resources, agricultural productivity, and human health. Our work strives to find, uplift, and scale solutions that improve our soils and long-term agricultural viability alongside positive water quality and quantity outcomes.
Our soil program promotes practices like cover cropping, compost application, and conservation tillage that help farmers preserve and regenerate the invaluable resource of healthy, arable soil. These strategies prevent soil erosion, increase water retention and infiltration, replenish organic matter, and promote microbial activity. Together, they create a self-sustaining cycle that conserves soil and water resources while regenerating soil health.
This means that as more farms adopt these practices, they can collectively reduce their reliance on synthetic fertilizers and water resources. Instead, they tap into renewable cycles that enhance agricultural productivity and environmental health.
Strawberry and leafy greens in California’s Monterey and Salinas Valleys, dubbed the “Salad Bowl of the World.” Photos: Pusher HQ
Snapshots of Circularity in our Soil Health Work
Healthy soils and water systems are sustained by complex, interconnected cycles. Water flows in rivers and through soil, supporting life and replenishing groundwater before returning to the atmosphere. In nature, the nitrogen cycle relies on diverse bacteria to pull this essential nutrient from the atmosphere and make it available to plants before being consumed by animals and passed back into the soil. Sustainable Conservation’s approach leverages these cycles to improve soil health while conserving our state’s most precious natural resources.
Using cover crops to retain water and nutrients
Sustainable Conservation explores how cover crops play a key role in the self-sustaining cycles that improve soil health and water availability while conserving resources. To better understand their potential, we convened over 100 experts to develop a report on how cover crops impact water usage in California’s Central Valley and support the implementation of the Sustainable Groundwater Management Act (SGMA). The report shows that cover crops can increase water infiltration and reduce runoff by over 40%, improving the soil’s ability to capture and store stormwater in groundwater aquifers below. By leveraging these natural cycles, farmers can enhance soil health and water retention, creating a regenerative system that benefits both crops and water resources. Now, we’re working with partners to pilot projects and create resources that help farmers tap into the full potential of cover crops in the SGMA landscape.
On the Central Coast, Sustainable Conservation partners with local Resource Conservation Districts, the Fertilizer Research and Education Program, and farmers to promote cover cropping that recuperates nitrogen for the next season. By planting cover crops in late fall, farmers can recover leftover nitrogen from the previous growing season — nitrogen that might otherwise leach into groundwater during winter rains. By absorbing excess nitrogen, these cover crops help safeguard water quality and return nutrients to the soil when they decompose in spring. This process could not only prevent groundwater contamination but also facilitate deeper infiltration of water and increases soil moisture retention year-round.
A side-by-side aerial of an orchard with (right) and without (left) cover crops. Photos courtesy of Andrew Gal, UC Davis
Harnessing orchard waste and manure exports for richer soils
Sustainable Conservation promotes solutions for safely using existing surplus manure to provide nutrients and build soil health. Current projects include expanding manure compost and demonstrating an innovative approach that combines whole-orchard recycling (WOR) with manure fertilizer application. WOR reduces air pollution from traditional orchard burning while putting valuable carbon from the trees back into the ground. Using surplus manure instead of synthetic fertilizer could provide the nitrogen necessary to break down carbon and ensure nitrogen availability for the next crop. Furthermore, by applying manure to recycled orchard material, we can improve soil structure, enhance nitrogen retention, build soil organic matter, and reduce the need for synthetic fertilizers.
Recycling almond shells for water quality protection
The Solutions in our Soil team is partnering with Dr. Joji Muramoto from UCSC to pilot the almond shell application onto fields on the Central Coast. These carbon-rich almond shells are considered high-carbon amendments (HCAs), which are used to stimulate the soil microbiome when applied to fallowed fields. This process could help capture nitrogen left in the soil and keep it in a plant-available format at the root zone until the next crop is planted, reducing nitrogen loss to groundwater. By applying HCAs, growers can help protect water quality while enhancing soil health and reducing the need for additional fertilizers in the following growing season.
“We see a lot of potential for this practice to help growers immobilize excess nitrate in winter and save it for the springtime when the crops need this critical nutrient. In addition, HCAs are a great opportunity to use a byproduct from the almond industry to address the Central Coast’s carbon deficit from intensive cropping rotation. Adding carbon to the nitrogen-abundant soil is a great way to improve our coastal soils’ health and mitigate nitrate leaching to our groundwater.”
Elliot Grant, Central Coast Project Manager
Circular nutrient management
Sustainable Conservation’s Manure Subsurface Drip Irrigation (MSDI) system strengthens California dairy farms’ natural nutrient circularity. In this system, feed crops are fertilized by nitrogen-rich manure, then harvested and fed to cows who in turn produce milk and, well, more manure. However, the traditional method of flood irrigation can saturate the field with more nitrogen than the crop can use, contributing to groundwater pollution and serious health risks for those who depend on that water for drinking and household use.
A manure separator in action. Photo: Pusher HQ
MSDI is just one tool farmers can use to keep the natural circularity of dairies intact while ensuring that manure remains a nutrient-rich asset and not a harmful pollutant. By blending liquid manure with freshwater and precisely applying this mixture at the root zone, the system safely reintroduces essential nutrients into the soil, reducing reliance on synthetic fertilizers and promoting long-term soil enrichment. As a result, MSDI not only minimizes groundwater contamination risks but also fosters healthier soils through sustainable nutrient recycling, helping to transform dairy by-products into an asset for agricultural productivity.