Cover crops compensate for water use with better soil moisture retention

Cover crop research conducted by a team of university researchers is now helping to inform and shape policy for implementing the Sustainable Groundwater Management Act (SGMA) in several counties in the San Joaquin Valley.

“The Madera County Regional Water Management Group appreciates the continued scientific discussion of SGMA-related issues and especially enjoyed hearing from cover crop researchers,” said Tom Wheeler, president of the Madera County Regional Water Management Group and Madera County Supervisor. “This is work that should be helpful to growers as they evaluate cover crops as part of their sustainable future.”

To help protect groundwater resources over the long term, Groundwater Sustainability Agencies (GSAs) develop Groundwater Sustainability Plans for their local regions.

“Our results suggest that water use by cover crops is negligible in most water years and that the long-term benefits can help GSAs achieve their management goals,” said Alyssa DeVincentis, former UC Davis Ph.D. student who worked on the project. “The impact of cover crops on soil moisture depends on species and management history, but in general, soil moisture at the end of the winter season did not differ between fields with winter cover crops and clean cultivated soils.”

From 2016 to 2019, UC Agriculture and Natural Resources researchers and their collaborators amassed very large datasets from almond orchards and tomato fields located between Chico in Butte County and Arvin in the Kern County. They used the data to quantify the changes in soil water storage and evapotranspiration that occur under cover crop and bare fallow conditions during the winter cover crop growing period – from November to March approximately.

The research team includes UC Cooperative Extension water specialists Daniele Zaccaria, Samuel Sandoval-Solis, and Jeff Mitchell based at UC Davis; DeVincentis now of Vitidore, Inc.; and Anna Gomes, Ph.D. student at Stanford University.

GSAs should first quantify the amount of water entering the groundwater bank through rainfall and surface water irrigation against the amount of groundwater withdrawn from all farms under the jurisdiction of the GSA. the GSA.

“To do this, many local GSAs are turning to remote sensing and evapotranspiration, or ET, modeling to provide data on the regional balance between groundwater depletions and recharges,” Mitchell explained.

“Because winter cover crops can appear on remote sensing images as water-consuming vegetation, the sole use of model-based data from satellites could become a drag on the practice used.”

“This approach may overlook the significant benefits that winter cover crops provide to farmers in the San Joaquin Valley like Justin Wylie, a Madera County almond and pistachio grower who works with the team. research,” Mitchell said. “He experienced the benefits of winter cover crops, including increased water infiltration, habitat and carbon for soil organisms, and reduced water runoff. “

Cover crops grown during winter may not use much soil water because ET during this time tends to be low. They also provide shading and cooling of the soil surface, which helps reduce evaporation from the soil. Additionally, Mitchell said cover crops can improve soil aggregation, pore space, and soil moisture retention.

Together, the benefits of cover crops appear to outweigh or compensate for their actual water consumption during the winter.

“Because GSAs need reliable and accurate information on this important issue and the possible downsides of relying solely on remote sensing as a way forward, our research was particularly timely in the context of SGMA,” said Daniele. Zaccaria, associate professor and water specialist. UC Cooperative Extension Management Specialist at UC Davis.

A presentation on their cover crop research is available on YouTube at https://youtu.be/x3xQlZ9EdCk. The webinar is intended for water agency personnel, but the information is relevant to anyone interested in how cover crops can influence San Joaquin Valley cropping systems and the water cycle. water, Mitchell said.

A peer-reviewed article on this cover crop research, “No-till yields of sorghum and garbanzo match or exceed standard tillage yields,” will appear in the first quarterly issue of California agriculture in 2022.

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