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Supporting Soil Health with Cover Crops in California

Soil pit exposes four tillage radish roots growing down into the soil. A yellow measuring rape reaches a depth of 18 inches.California is a major agricultural state with over 400 commodity crops, valued at almost $50 billion in 2018. The state produces one third of the vegetables and two-thirds of the fruits and nuts consumed in the US. The two largest commodity crops are grapes and almonds and these high-value perennial crops have increased in acreage in recent years, replacing row crops and pasture. California lags behind other states in sustainable practices and cover crop adoption for these cropping systems.  Implementation of cover crops within California cropping systems is estimated at only 5%. The Mediterranean climate, recent drought and cultural and economic reasons all play a role in the low adoption rate. It is recognized that there is also a lack of knowledge about well adapted cover crop species and cultivars, and suitable management strategies for the diverse cropping systems.

To address the need for information on cover crop species and cultivars adapted to California, the USDA-NRCS Lockeford Plant Materials Center (CAPMC) conducts onsite studies and field plantings. Assistance with cover crop selection, specifically for California, is provided in several documents and online tools including the  NRCS eVeg Guide, a Technical Note: Cover Crop Chart for California, Study Report: Cover Crop Variety Adaptation Trial, and several Case Studies: Soil Health Soil Properties in a California Prune Orchard, Winterkill Cover Crop Demonstration and Maturation Dates of Warm Season Cover Crop Species. Case studies are particularly helpful for Service Center staff and producers due to the diverse cropping systems and large rainfall and temperature gradients across California.

Field Day at the Lockeford PMC; a mixed cover crop in the foreground is dominated by white blooms of tillage radish. In the background attendees are gathered around a blue canopy.The CAPMC also serves as a living laboratory for the effects of conservation management practices on soil health, including cover crops. The CAPMC is located on the eastern side of the San Joaquin Valley and sits on a historical flood plain of the Mokelumne River.  The soils are very deep, well-drained, fine sandy loams.  Previous management practices included disking and herbicide use for native seed production, causing a degradation of soil structure and a reduction in soil organic matter. This is typical for agricultural landscapes in the Central Valley where the hot dry summers rapidly oxidize organic matter in unprotected soils. NRCS has held Soil Health Trainings for Conservation Planners at the CAPMC to illustrate the differences in soil health under different management practices.  Examples include degraded soil with poor structure from frequent tillage and less than 1% organic matter, regenerating soils under annual cover cropping with minimal tillage, undisturbed annual and perennial grass systems, and hedgerow plantings with improved soil structure and increased soil organic matter.

NRCS partners including the California Department of Food and Agriculture (CDFA), Resource Conservation Districts and the University of California (UC) recognize the efforts and contributions of the CAPMC in support of the Soil Health Programs. The CDFA’s Healthy Soils Program awarded the UC system with a grant in 2019 to monitor the NRCS Field Border Practice for Soil Health benefits at the CAPMC.

For more information on the Lockeford Plant Materials Center please contact Margaret Smither-Kopperl,