- Author: Jeffrey P Mitchell
Information on the dynamics of long-term use of winter cover crops in California's San Joaquin Valley will be shared with online participants as part of the Desert Southwest Soil Health Webinar (https://www.eventbrite.com/e/desert-southwest-soil-health-webinar-tickets-107732693386), slated for July 23rd from 8 AM through 6 PM.
“This will be one of the first outlets in which we'll share our 20-year findings on both the costs and benefits of using cover crops to improve agroecosystem biodiversity and the efficiencies of the C, N, and water cycles in SJV annual cropping systems,” says UC ANR's Jeff Mitchell, whose presentation on conservation agriculture falls in the 10:30 AM – 3:00 PM “Practices to improve soil health,” slot on the day-long program.
Mitchell will describe how over the course of the project that was characterized by recurring drought, a total of 37 tons of aboveground cover crop biomass representing 1580 lbs N and 14.8 tons C per acre was produced with a total precipitation of 127 inches and 16 inches of supplemental irrigation in that was applied in four of the years. These inputs averaged 3,695 lbs of organic matter or 0.79 tons of C annually. Year-to-year variability was quite large ranging from 8,818 lbs OM in 2000 when supplemental irrigation was applied, to 54 lbs/ac in 2007 when, as in most years, no irrigation was applied to the cover crops. The cover crops were typically seeded by November 15 and terminated around March 15 of the following year accounting for a growth period of 120 days capturing solar energy by the “green ground cover”, and living roots in the soil for about 90 additional days during the year relative to the standard practice system which was bare during this time. Based on cover crop growth during years when supplemental irrigation was applied, Mitchell estimates that an average of 6,082 lbs of dry cover crop biomass might have been produced with a modest input of 2 inches of water. Even greater amounts of cover crop biomass – approximately 12,000 lbs of dry matter per acre as is typically achieved with winter silage triticale crops in SJV dairies - could be produced were cover crops “treated more like cash crops” with additional supplemental strategically timed irrigation in a cropping system as in other regions of the US. He'll also be showing participants via recorded video clips just how this sort of sustained cover crop use improves key soil health indicator properties and function.
CCA and PCA credit for the online webinar have been requested.
Photo caption
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UC ANR Cropping Systems Extension Specialist, Jeff Mitchell, shown sampling winter cover crop aboveground biomass in longstanding conservation agriculture study of the impacts of reduced disturbance, cover crops, and surface residues on soil function, productivity, and ecosystem services at the Conservation Agriculture Systems study site in Five Points, CA
New data on cover crops to be presented July 23rd!
- Author: Jeannette E. Warnert
"Attributing ecosystem services to farming is an emerging trend in assessing the benefits of agricultural operations," said Jeff Mitchell, UC Cooperative Extension specialist in the Department of Plant Sciences at UC Davis. "Resource management systems on today’s farms can provide significant benefits to air, water, and soil resources and furnish wildlife habitat. We've now determined that farmers who use cover crops and no-till practices are furnishing still more ecosystem services."
Since 1999, a team of UC researchers, local farmers, Natural Resource Conservation Service conservationists and private sector partners have compared plots at the UC West Side Research and Extension Center managed with cover crops and no tillage to adjoining plots managed with traditional tillage approaches.
"We have seen striking changes in soil properties after sustained cover cropping and no-till management," Mitchell said.
With eight inches of supplemental irrigation over the 14-year period, cover crops produced more than 19 tons of organic matter or about 7 tons of carbon per acre. This biomass resulted in a 23 percent increase in soil carbon in the cover cropped system that was ‘green manured,’ or incorporated back into the soil with tillage, and a 74 percent increase in soil carbon in the no-till cover crop system.
The research team also reported similar increases in total soil nitrogen, with 19 percent more in the green manured cover crop and 59 percent more in the no-till cover cropped system. The value of these changes relates not only to improving favorable soil attributes – such as water holding capacity, reduced runoff and more available nitrogen – but also to the fact that these soils are now serving as greater 'sinks' for carbon and nitrogen.
"That means there is reduced likelihood these elements will enter the atmosphere as greenhouse gases or be leached to groundwater," Mitchell said.
Mitchell said the team also measured increased levels of soil aggregation, which is related to higher water infiltration and greater soil water storage capacity when cover crops and no-tillage are used.
This long-term research continues at the West Side Research and Extension Center to further determine tradeoffs associated with cover cropping and no-tillage practices in terms of water use, input costs and ecosystem service benefits. Dan Munk, UC Cooperative Extension advisor in Fresno County and project partner, points out that this long-term 'systems' work is important because it allows the opportunity to fully assess both the overall costs and benefits of alternative practices.
More information may be found at the Conservation Agriculture Systems Innovation website at http://casi.ucanr.edu/.
