Nutrient Management Research Database

Agricultural management has a significant impact on the amount of greenhouse gases emitted by cropped fields. Alternative practices such as winter cover cropping and avoiding over-fertilization can decrease the total amount of greenhouse gases that are produced. Policymakers are considering a structure in which parties (such as factories) who exceed their greenhouse-gas emissions cap can pay incentives to encourage farmers to adopt practices that curb greenhouse gases. Based on data from field studies and an ecosystem computer model, we assessed impacts on yields and the total potential for reducing greenhouse gas emissions of certain alternative practices in California.

This study uses an ecosystem computer model, to simulate greenhouse gas emissions from agricultural management practices.  The study objectives where to calibrate the model to California conditions, to use the model  to evaluate changes in crop resulting from alternative management practices, and to evaluate the potential of these practices for greenhouse gas mitigation.

 Long-term field experiments, including the Long-term Research on Agricultural Systems (LTRAS) project at UC Davis, the Sustainable Agriculture Farming Systems (SAFS) project conducted at UC Davis from 1989-2000,  the West Side Research and Extension Center (WSREC) in Five Points, and Field 74 in Yolo County, were used to help calibrate the model. These sites included corn-tomato, tomato-safflower-corn-wheat-bean, tomato-wheat, corn-sunflower, chickpea, and tomato-cotton rotations.  Alternative treatments included legume cover cropping, use of poultry manure, and conservation-tillage.

The DAYCENT model was used to simulate yields and greenhouse gas emissions.  The model simulates plant production, water flow, heat transport, soil organic carbon dynamics, nitrification, denitrification, and methane oxidation.  Different management options were specified, and data from the field experiments and the literature were used to adjust the model to CA conditions.  The Sacramento and San Joaquin valleys were considered separately.  Only annual and nonwoody perennial cropping systems were considered, and the study was limited to rice, alfalfa, cotton, tomatoes, winter wheat, corn and safflower, sunflower and melon crops.  

Key results of this study include:

• The model predicted that most crop yields would not be strongly effected by the assessed alternative management practices.  
• Manure application, winter cover cropping or conservation tillage alone resulted in modest reductions of greenhouse gas emissions.
• The combination of manure applications with winter cover cropping was an efficient practice for mitigating greenhouse gas emissions.
• Increases in soil organic carbon made up up to 90% or carbon offsets resulting from alternative management practices.  
• When manure was used to replace a portion of mineral fertilizer, nitrous oxide emissions decreased.

poultry manure was added to some organic systems, safflower was planted in a tomato-safflower-corn-wheat-bean rotation at the SAFS site.