“The soil-water interaction under various soil management practices will be quite clear if we do get the increased rainfall this winter that has been forecast,” Mitchell said. “Soil high in organic matter and covered by plant residue will allow increased water infiltration and storage, less water runoff and, on a large scale, increased groundwater recharge.”
Mitchell, a UC ANR Cooperative Extension specialist based at the UC Kearney Agricultural Research and Extension Center, has researched conservation agricultural practices for nearly 20 years. He is chair of UC ANR's Conservation Agriculture Systems Innovation Center (CASI), a collaborative organization involving researchers, farmers and industry partners who aim to increase the use of conservation practices in California.
Most farmers in the San Joaquin Valley till their land after harvesting row crops believing they have to create clean planting beds for seeding and establishment of subsequent crops. The practice, Mitchell said, is influenced mainly by tradition.
Research at the UC West Side Research and Extension Center that has been ongoing since 1999 has documented striking changes in plots after sustained cover cropping and no-till management. In addition to improved soil properties, the plots managed with conservation agriculture practices have comparable or in some cases higher yields, less soil water evaporation, lower dust emissions and, because of the higher soil organic matter, sequestered more carbon than adjacent plots managed using conventional practices.
In other parts of the world, generating and preserving plant residues are an indispensable part of farm management. Increasingly in California, farmers are implementing conservation tillage practices.
In addition to protecting soil from driving rain and wind in the winter, the plant residues provide important benefits in the summer. The plant residue on the surface shades the soil, providing a beneficial cooling effect, and soil with high organic content has higher moisture holding capacity.
“A number of studies from both irrigated and rain-fed regions around the United States where no-tillage is used have reported annual irrigation savings of as much as four to five inches,” Mitchell said.
Good soil management also promotes its biological diversity, noted Randal Southard, a CASI member and professor in the Department of Land, Air and Water Resources at UC Davis.
“Reducing soil disturbance, keeping the soil covered with plant residues and promoting high biological diversity provide soils with resilience – the ability of soils to accommodate changes in a wide array of environmental conditions,” Southard said. “Soil resilience or soil health is similar to how we think of human health, including overall well-being and the ability to resist diseases and other maladies.”
Soil is getting increasing attention in California and worldwide. The United Nations declared 2015 the International Year of Soils to raise awareness about a substance that is the very foundation of life on earth. The USDA's Natural Resources Conservation Service launched a Soil Health Campaign and the California Department of Food and Agriculture has created a Healthy Soils Initiative.
A network of soil health demonstration evaluations is now being created by CASI in California. Local teams are being organized in Sacramento, Mendocino, Stanislaus, Fresno and Kern counties involving Resource Conservation Districts, USDA Natural Resources Conservation Service and UC ANR Cooperative Extension researchers and local farmers. The farmers will set aside small comparison plots to evaluate practices that are believed to improve soil health and the researchers will have a role in monitoring and documenting changes.
“Each of these efforts points to the pivotal role healthy soils have in food security, agricultural sustainability and climate change resiliency,” Mitchell said.
Author: Jeannette Warnert