Pierce, L. Danielle (University of California Davis, 1010 Wickson Hall, One Shields Ave., University of California, Davis, CA, 95616; Phone: 530-754-7144; Fax: 530-752-0382; Email: dlpierce@ucdavis.edu) 

Conservation Tillage of Cover Crops as a Means of Improving Carbon

Storage in California Vineyards
 
Danielle L. Pierce *, K. L. Steenwerth, D. R. Smart
 
There are nearly one million acres of grapes in California and only about 16% are sown to cover crops, suggesting there is potential for increasing this management practice in vineyards. Tillage of cover crops generally increases soil respiration by bringing organic residue in contact with soil microbes and exposing it to soil conditions that favor mineralization like higher moisture content and aeration. Tillage also breaks-up aggregates and makes previously encapsulated C available to mineralization processes. We examined the carbon sequestration potential of conservation tillage of a vineyard cover crop in the Napa Valley, CA. A cover crop of barley was planted between vineyard rows in November of 2003, and subplots were isotopically labeled with 13CO2. We have shown in the first season of this investigation that 13CO2 labeling can be used to monitor C turnover by estimating source 13C content of soil respired CO2. We observed immediate 13C enrichments in soil respired CO2 in the conservation and conventional tillage treatments that were due to the decomposition of isotopically labeled fresh plant material. An ensuing depletion of 13C may have indicated a reduction in available 13C labeled soil organic carbon (SOC). The conservation tillage treatment showed a slower rate of change (13C loss) relative to the conventional tillage treatment, but the rate of change was strongly dependent on precipitation events following summer drought. Conventional tillage decreased soil moisture overall, but also increased maximum soil temperature and the rate of SOC mineralization. Our investigation is providing information on how minimum tillage of cover crops might help mitigate the observed increase in CO2 concentration in the atmosphere.