- Author: Jeffrey P. Mitchell
September 3, 2021
Michiel Bakker, the Vice President for Global Workplace Programs for GOOGLE, along with Douglas Gayeton, the creative leader for The Lexicon of Sustainability (https://www.thelexicon.org/ ), spent a full day on September 3, 2021 first visiting the NRI Project field in Five Points, CA and then the farms of John Diener right up the road, and of Phil Foster in Hollister, CA. The purpose of their visit was to learn about and see efforts that are being made to realize conservation (or more recently, “regenerative”) agriculture systems here in California. CASI's Jeff Mitchell coordinated the day's tour that also included retired Madera, CA organic farmer, Tom Willey.
While at the NRI study site, the group looked at several reduced disturbance pieces of equipment and also witnessed the increased aggregation of long-term no-till and cover cropped soils in the NRI field compared to that of standard tillage.
At Red Rock Ranch, the Five Points farm of Diener, the group along with John's son, Justin, talked about water issues that California is facing as well as efforts the Dieners are making to address water shortages. They also learned what goes into the large organic tomato fields that they visited and learned about the minimum pass tillage practices that they use.
At Pinnacle Organically-Grown Produce, the Hollister, CA farm of Foster, the visitors saw a variety of Phil's innovations including his on-farm compost production techniques, his use of strip-tillage, and his development of the use of single-line cover crops that economize greatly on seed and water.
- Author: Jeffrey P Mitchell
- Author: Jeffrey P Mitchell
- 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
Image_0320
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
Even on the west side of the San Joaquin Valley, where average rainfall is a mere 7 inches per year, farmers can reap the benefits of winter cover crops without the expense of irrigation, University of California research has found. Growing a winter cover crop helps retain soil nitrogen – keeping it from leaching into groundwater – improves water infiltration, reduces runoff, increases soil organic matter and boosts long-term soil fertility.
Moreover, a vigorously growing cover crop can smother winter weeds, reducing or eliminating the need for herbicides or tillage between crops.
“Despite the many and varied benefits of cover cropping that are increasingly seen by farmers in other parts of the country, the vast majority of Central Valley farmers currently do not use them,” said Jeff Mitchell, UC Cooperative Extension specialist in the Department of Plant Sciences at UC Davis. Mitchell, a cropping systems expert, is based at the Kearney Agricultural Research and Extension Center in Parlier, Calif.
The costs and benefits of winter cover crops are being examined in an ongoing trial at the UC West Side Research and Extension Center in Five Points, Calif. Initiated in 2000, the trial is led by Mitchell, William Horwath, a professor in the Department of Land, Air and Water Resources at UC Davis, and Dan Munk, UC Cooperative Extension advisor in Fresno County, a cotton and soils expert.
Mitchell said the West Side trial addresses valley farmers’ primary concern about cover crops – water.
“When water is short, as it has been in many recent years, farmers wonder how inserting an extra crop that doesn’t bring an immediate return on investment makes sense,” Mitchell said. “But our work over the last 12 years has demonstrated that cover cropping ‘on the cheap’ – relying only on rainfall for irrigation – supplies many benefits and doesn’t cost much.”
Rainfall during the November to March winter growth period in Five Points averages 7 inches, slightly less than the 30-year average annual rainfall of 7.6 inches for the site. Winter rainfall has varied considerably during the trial, from a low of 2.9 inches in 2003 to a high of 11 inches in 2006.
From 2000 to 2010, a cover crop mix of triticale, ryegrain and pea was grown at a seed cost of $55 per acre (2012 dollars). In 2011 and 2012, the researchers used a mixture of fava bean and “tillage radish” for the cover crop, at a cost of $50 per acre.
Tillage radish is a large-rooted winter annual being marketed for its ability to improve soil condition. It’s thick, tuberous roots break up the soil surface. When it is killed in the spring and the roots decompose and shrivel, it leaves behind channels that help with aeration and water infiltration.
Over the course of the UC trial, an average of 3,400 pounds of dry biomass per acre was produced by the cover crops each year with rainfall alone. Productivity generally related to the amount of rain, with as little as 65 pounds of dry biomass per acre in 2007, when rainfall was 5.2 inches, and 6,400 pounds in 2005, when 10.1 inches of rain fell.
The timing of rainfall was also important. Rain is needed early to establish the crop and late in the season to sustain its growth when the temperature warms.
Over time, growing cover crops results in a significantly higher amount of carbon in the top foot of soil. Following eight years of cover cropping, soil carbon values in the standard tillage cover crop system, in which the cover crop was treated as a green manure and incorporated into the soil at a depth of 10 inches, was 12.2 tons of carbon per acre. Where cover crops were combined with conservation tillage, the researchers measured 12.8 tons per acre. In areas managed with conservation tillage and no cover crop, 11.7 tons per acre of carbon was in the top foot of soil. Under standard tillage and no cover crops, currently the common practice in the San Joaquin Valley, soil carbon came in at 9.9 tons per acre.
In addition to improving soil quality, farmers are investigating whether storing extra carbon in the soil will make them eligible for selling carbon credits under California Assembly Bill 32, the Global Warming Solutions Act.
“Sequestering carbon in farmland could be a means of mitigating global warming from greenhouse gas emissions,” Mitchell said. “We are working with farmers to develop a record of performance so they can document their potential for storing more carbon using conservation tillage and cover crops.”