Nutrient Management Research Database

California growers could reap financial benefits from the low-carbon economy and cap-and-trade system envisioned by the state’s AB 32 law, which seeks to lower greenhouse gas emissions statewide. Growers could gain carbon credits by reducing greenhouse gas emissions and sequestering carbon through reduced tillage and increased biomass residue incorporation. First, however, baseline stocks of soil carbon need to be assessed for various cropping systems and management practices. We designed and set up a pilot soil carbon and land-use monitoring network at several perennial cropping systems in Northern California. We compared soil carbon content in two vineyards and two orchards (walnut and almond), looking at conventional and conservation management practices, as well as in native grassland and oak woodland. We then calculated baseline estimates of the total carbon in almond, wine grape and walnut acreages statewide. The organic walnut orchard had the highest total soil carbon, and no-till vineyards had 27% more carbon in the surface soil than tilled vineyards. We estimated wine grape vineyards are storing significantly more soil carbon per acre than almond and walnut orchards. The data can be used to provide accurate information about soil carbon stocks in perennial cropping systems for a future carbon trading system.

• Four field sites were established in 2008 in an almond orchard, a walnut orchard and two wine grape vineyards.
• Management practices assessed for impact on soil C accumulation included cover cropping, no tillage, conventional and organic farming practices.
• The soil monitoring network consisted of 95 triangular microplots marked with a gps location device distributed among the different cropping systems.
• 3 Soil samples were taken up to 1 meter (3.28 ft) depth in each microplot.  Samples were analyzed at top (0-7.9 inches) middle (7.9-19.7 inches) and deepest (19.7 to 39.4 inches) depths for total carbon and nitrogen, pH, bulk density and soil moisture.  

• Bulk density results suggested a plow layer at the middle depth in vineyard and almond systems.
• Soil C and N were higher in no-till when compared to conventional tillage in one vineyard.  
• Statewide estimates indicated that wine grapes under common management practices store a large amount of carbon.