Chapter 10 - Management to Reduce Greenhouse Gas Emissions in Western U.S. Croplands

Abstract

Agriculture is a major activity in the western U.S. with approximately 57 million ha of harvested cropland of which 27% is irrigated; however, irrigated crops account for a high proportion of the economic returns because of their high economic value. We sought to summarize greenhouse gas (GHG) flux research from crop production systems in the western U.S. published from 2005 to 2011. Limited GHG emissions data were found from irrigated cropping systems in California (grain, rice, vegetable, orchards), Texas (cotton), Colorado (corn), and Washington (corn and potato), and from dryland wheat systems in Montana and North Dakota. Converting from conventional tillage (CT) to minimum-till (MT) or no-till (NT) production generally sequestered soil organic carbon (SOC) and reduced carbon dioxide (CO 2 ) emissions in many cropping systems, but not all. Methane (CH 4 ) flux was not greatly influenced by crop management practices, except in rice and manure production systems. Nitrous oxide (N 2 O) emissions were affected by N availability, climatic factors, irrigation, and crop management practices, and tended to be lower under dryland than irrigated cropping conditions. Reducing N fertilization rate and selecting the right N source can reduce N 2 O emissions as much as 50%. Use of microjet sprinkler or subsurface drip irrigation reduced N 2 O emissions in vineyards and orchards as much as 50% compared to surface drip systems. Available GHG data could be used to verify models and develop local mitigation practices, but due to the large diversity of cropping systems and ecoregions, and a lack of representative cropping system GHG databases, generalized mitigation recommendations for the western U.S. are not possible at this time.