Center for Regenerative Agriculture and Resilient Systems

Good News about Water Usage and Cover Crops in California

by CRARS staff member Sheryl Karas. M.A.

Cover crops in a nut orchard at the University Farm

California farmers face many challenges when it comes to water usage, soil health, crop yields, and farm resiliency, especially in the face of multiple years of drought followed by cropland-ravaging extreme winter storms. One of the most promising ways to address this is by using cover crops. However, many farmers are hesitant to adopt this practice due to concerns about cost, how much water the cover crops might need, and the potential that those crops could have an effect on cash crop yields. However, new research from UC Davis indicates that cover crops can actually be a cost-effective strategy with little to no effect on water usage when handled well. Let’s address the concerns by looking at the benefits, the latest research, and tips for success (including how to pay for it).

Benefits of Cover Crops

Cover crops are crops grown specifically to improve soil health, reduce erosion, and enhance nutrient cycling. They are planted in between cash crops or during fallow periods and are typically not harvested for profit. Instead, they are incorporated back into the soil to provide organic matter and nutrients for the next crop. Some of the benefits of cover crops include: 

  • Improved Soil Health: Cover crops help to improve soil structure, reduce compaction, and increase water-holding capacity. They also promote the growth of beneficial microorganisms, which can improve nutrient availability and reduce the risk of plant diseases.
  • Reduced Soil Erosion: Cover crops protect soil from erosion by reducing the impact of wind and rain through anchoring the soil with their root systems, reducing surface runoff, improving soil structure, and increasing water infiltration rates.
  • Increased Nutrient Availability: Some cover crops such as legumes have the ability to fix nitrogen from the air and convert it into a form that plants can use. When the cover crop is incorporated into the soil, the nitrogen is released, providing a natural source of fertilizer for the following crop. Additionally, when a cover crop is terminated and allowed to decompose, other nutrients such as phosphorus and potassium are released back into the soil.
  • Increased organic matter: Cover crops contribute to the buildup of organic matter in the soil. In addition to playing a significant role in the above benefits, this can significantly increase soil carbon accrual when combined with no-till or reduced tillage.
  • Weed Suppression: When cover crop residue is left on the ground as a mulch, they shade the soil, reduce weed seed germination, and release chemicals that inhibit weed growth.
  • Biodiversity: Cover crops can attract beneficial insects and microbes that improve soil health and pollinate crops.
  • Water Use Efficiency: While cover crops do use and transpire some water as all crops do, the overall effect of keeping the ground covered with roots in the ground all year is increased water infiltration and retention in the soil, reduced water runoff, and reduced evaporation.

Despite these benefits, it can feel challenging to incorporate cover crops into a farmer’s practices, especially since water use in regards to cover crops has been a hotly debated topic during the more than 10 years of drought in California. The convention is to let the land lie fallow between cropping seasons (bare and unwatered.) Proof of the practice’s water efficacy and cost/benefit analysis under these conditions has been sorely needed.

UC Davis Research on Winter Cover Crops

In January of 2022, UC Davis published the results of a three-year study(opens in new window) that took place on 10 commercial farms and research sites in California’s Central Valley between Chico in Butte County and Arvin in Kern County. The study examined the impact of winter cover cropping on soil health and water retention in irrigated agricultural systems with a focus on almond and tomato crops, which are two of the most common crops grown in the region.

Three cover crop systems were included in the study and then compared to control fields left bare at the same site. The systems included:  1) a cover crop in processing tomato fields; 2) a cover crop planted in between rows of almond trees; and 3) allowing whatever native vegetation was available (such as grass) to grow in between the almond tree rows. The planted cover crops were a mix of legumes, grasses, and brassicas.

The results were impressive. Researchers found that the cover crop fields had higher levels of soil organic matter, soil nitrogen, and microbial activity, indicating improved soil health. In addition, the cover crop fields had higher levels of water infiltration and retention, meaning that they were better able to hold onto water during periods of drought or water stress. The researchers found that the cover crops did not compete with cash crops for water, and that the same amount of water used in the control fields without cover crops was able to support the same amount of crop yield in the cover crop fields. In one case in Davis, there was heavy rainfall at one point during the study. The water loss via evapotranspiration was greater in the bare control plot, showing that use of cover crops improved water retention.

This study provides important evidence of the benefits of winter cover cropping in California's Central Valley, particularly for improving soil health and reducing water usage in agricultural systems. The findings suggest that cover crops can help farmers make more efficient use of their water resources, potentially reducing the need for additional irrigation, and providing environmental benefits such as reduced erosion and improved water quality. The researchers believe that California growers could adopt winter cover cropping without altering their current irrigation plans and water management practices. 

Additional Studies

The results of the UC Davis study are the first done in California but they are corroborated by several studies across the globe.

For example, a study published in the Soil Science Society of America Journal(opens in new window) in 2022 found that cover crops did not reduce corn yield or water use in a corn-soybean rotation in Iowa. The researchers found that the cover crops helped increase soil water content and reduce soil erosion, indicating improved water use efficiency and soil health. 

A meta-analysis looking at multiple studies(opens in new window) around the world on cover crops and water usage published in 2021 in the Agricultural Water Management journal showed good results when using cover crops on precipitation storage efficiency and soil water storage at succeeding crop planting, and decreased evapotranspiration. There was a limited effect on subsequent cash crop yield and water use efficiency overall but better results were found in humid climates. The researchers concluded that choosing different cover crops in arid regions and leaving the crop residue on the ground would lead to the best results.

All recent studies agree that timing of cover crop planting and termination and prudence in choosing the right cover crops for the climate was essential for the most positive impact with the least risk.

Tips for Success

To successfully incorporate cover crops into their farming practices, farmers are advised to:

  • Set clear goals for their cover crops, such as improving soil health, reducing erosion, suppressing weeds or crop pollination.
  • Choose the right cover crop for their specific goals, soil and climate conditions.
  • Plan cover crop rotations carefully to avoid competition with cash crops and minimize pest and disease pressure. 
  • Monitor water usage and adjust irrigation as needed to avoid over or under watering.
  • Use appropriate planting and management techniques to maximize cover crop benefits and minimize costs.
  • Seek out educational opportunities or technical assistance to assist in decision-making through local college, universities and extension programs, local Regional Conservation District Office (RCDs), non-profit organizations, and government agencies that provide workshops, field days, training programs, and technical assistance on cover crop use.
  • Take advantage of financial incentive programs such as the ones listed below to make the transition affordable and find the technical support you need.

Funding Sources

There are several financial resources available to California farmers who want to add cover crops to their farming practices but are worried about the cost. Here are some options:

With so many opportunities to fund and help support your success, it can really pay off to add cover cropping to your farming or ranching practices. Several of these programs can be used at the same time. Interested farmers and ranchers are encouraged to take advantage of as many opportunities as possible.

What Do Farmers Have to Say About Cover Crops?

Listen to two farmers who took part in the UC Davis study mentioned above— Justin Wiley of Madera, CA, and Steven Strong of Burrel, CA.