- Author: Yoni Cooperman
Alfalfa has a long and storied history in California agriculture. First introduced in the state during the gold rush of 1849-1850, California now leads the nation in alfalfa production. Between 2013-2015, an average of 815,000 acres of alfalfa were harvested in the state. Statewide alfalfa yields increased to 5,451,000 tons in 2015 and California now accounts for over 9% of total U.S. production. Alfalfa serves as an important source of hay while also proving useful as a ‘green manure' that can provide nitrogen for the following crops. That being said, alfalfa has relatively high water demands, a particularly vexing issue due to the current statewide drought. While the majority of alfalfa cropping systems utilize flood irrigation, the potential for utilizing sub-surface drip irrigation (SDDI) has become an attractive option to many growers seeking to reduce water usage. The type of irrigation utilized can also influence nitrous oxide (N2O) emissions. N2O is a potent greenhouse gas 300 times more powerful than carbon dioxide in warming the planet. Agriculture accounts for more than 60% of statewide N2O emissions from human activity. It has been shown that SSDI reliably reduces N2O emissions in other cropping systems.
UC Davis Land, Air, and Water Resources graduate student Ryan Byrnes recently completed a year-long study investigating the potential for SSDI to mitigate N2O emissions from alfalfa production. The study compared rates of N2O production in side by side alfalfa systems, one utilizing check flood irrigation while the other had a SSDI system installed. “We found that yearly emissions were significantly reduced by the adoption of SSDI.” Sustained soil moisture drives N2O emissions, and he noted that “SSDI keeps the soil surface dry, potentially reducing N2O emissions.” While large bursts of N2O emissions are often observed following the rewetting of dry soil, Ryan pointed out that “the pulse emissions in the SSDI plots was lower than in the flood plots.” The emissions following the first rains were not high enough in the SSDI plots to offset the reductions observed through the rest of the season. While additional studies are needed to draw any definitive conclusions, the findings of this study are encouraging. Stay tuned to this space for reports on future studies investigating the potential for SSDI to mitigate statewide N2O emissions.
- Author: Aubrey Thompson
In June, the California Department of Food & Agriculture (CDFA) will release a call for grant proposals from farmers and ranchers to fund management practices that improve soil health. CDFA will provide almost $4 million in grants for practices such as mulch and compost addition, conservation plantings, cover cropping, reduced tillage, and more, and another $3 million for demonstration projects. The funding comes from the state's cap-and-trade program and must be invested in activities that reduce greenhouse gas emissions and/or sequester carbon by improving soil health.
Join us on this webinar to get a preview of the program. The webinar is offered in partnership with the UC Sustainable Agriculture Research and Education Program (SAREP) and California Climate & Agriculture Network (CalCAN).
Topics that will be covered:
•What policies led up to the launch of the Healthy Soils Initiative?
•What practices will be incentivized?
•What will be required of growers in applying?
•What is the timeline and next steps?
In addition, webinar participants will hear about UC SAREP's work related to healthy soils.
Details:
Tuesday, May 30
10:00am-11:00am
Register for the webinar here:
https://zoom.us/meeting/register/0f72f8e741098877cde7dc3c8da9331e
With questions about the webinar, contact Aubrey Thompson at UC SAREP - abthompson@ucdavis.edu
With questions about the Healthy Soils Initiative, contact Renata Brillinger at CalCAN - renata@calclimateag.org
- Author: Yoni Cooperman
- Contributor: Deirdre Griffin
In the on-going quest to develop sustainable agricultural practices, growers are looking for new and inventive technologies. In this blog post, we'll focus on biochar, one such technology that has been a focus of intense research in recent years. Biochar is produced by burning organic material at extreme temperatures as high as 1600° F with little to no oxygen available. Oftentimes biochar is a by-product of energy production, but it can also be produced solely to be used as a soil amendment.
There's a few reasons growers might incorporate biochar into their cropping systems. Biochars' high surface area allows it to act as a reservoir of water while increasing the retention of nutrients such as calcium, magnesium, and ammonium. This is especially useful in more sandy soils with low cation exchange capacity. Biochar can also serve as a liming agent to increase soil pH, which increases nutrient availability in acidic soils. Additionally, biochars with high ash content can contain calcium and potassium that plants can use. Biochar inputs are also high in carbon. Stay tuned to this blog for another post highlighting the potential for biochar to increase soil carbon storage.
Feedstock – the organic material used to produce biochar – varies widely. Common feedstocks include wood chips, nut shells, and grasses. In California nut shells stand as a potentially useful source of feedstock due to the large nut industry. Biochar can also be produced from manures. Both feedstock and production temperature influence how biochar will behave in the soil. Dr. Sanjai Parikh's lab at the University of California, Davis has developed a biochar database that includes both of these characteristics.
Initial interest in biochar stemmed from the study of the Terra Preta soils in South America. These generally low fertility, acidic oxisols were able to sustain higher productivity than nearby non-Terra Preta soils while also accumulating organic matter. One of the reasons for this productivity was the addition of charcoal by indigenous farmers thousands of years ago. The hope was to mimic this in a modern agricultural setting.
Like most agricultural practices, biochars present some challenges for effective integration into a cropping system. Like compost or manure, it can be difficult to predict when nutrients from biochar will become plant available or how a char will interact with a particular soil. Different soil types require different rates of biochar application. For example, a clay loam would require more biochar to increase pH when compared to a sandy soil as a result of the clay loam's higher buffering capacity (see figure below).
UC Davis Soils and Biogeochemistry graduate student Deirdre Griffin is researching how soil microbes respond to biochar additions. She explains that “while biochars can sometimes serve as a source of labile carbon to spur microbial activity, some chars can give off inhibitory compounds that may reduce microbial activity.” In particular, she is looking at whether biochars with high sorption capacity (i.e. the ability to hold on to compounds in the soil) can interfere with signaling between legumes and soil bacteria that fix nitrogen and make it available to plants. She is careful to note that “others have found biochars to increase nodulation in legumes.”
All in all, “the leaders in the field recognize that while there are many benefits of biochar, there can also be negative impacts…There was a burst of [research] excitement followed by some backlash, and now things are starting to even out.” Biochar can serve as a tool for sustainable production systems, but it isn't appropriate for every situation. Continued research will illuminate what types of biochar are suitable for different soils.
