Assessment of Soil and Residue Carbon and Nitrogen and Greenhouse Gas Emissions From Soils Beneath Irrigated and Dryland Alfalfa and Austrian Winter Pea.

Utilization of legumes in place of fallow has been shown to decrease input costs and improve nitrogen use efficiency (NUE) in many crop rotations.  However, Northern High Plains dryland cash crop production relies on summer fallow for water storage and little is known about the impact of replacing summer fallow with legumes on soil and plant nutrient cycling. The overall goal of this research is to estimate the impact of legumes in irrigated and dryland crop rotations in Northern High Plains on seasonal soil water content and contributions to agroecosystem nitrogen (N) budgets. To accomplish this goal, we monitored soil N mineralization, greenhouse gas (GHG) emissions, plant biomass and C and N content from dryland and irrigated perennial legume (alfalfa) and annual legume (Austrian winter pea).  To our knowledge, this is the first inventory of N₂ fixation and GHG emissions from legumes in the Northern High Plains systems.  We hypothesize that irrigated legumes will contribute larger amounts of N-rich residue and mineralized N to the soil and greater GHG emissions when compared to dryland system. Consequently, soils from dryland legume production will have lower residue decomposition and will accumulate more surface plant residue for the subsequent crop. Results from spring 2011 soil and plant biomass and GHG emissions will be presented.