Greenhouse Gas Emissions from an Irrigated Dairy Forage Rotation as Influenced by Fertilizer and Manure Applications

Information is needed regarding the effect of N source on greenhouse gas (GHG) emissions from irrigated semiarid agricultural soils. We report N2O, CO2, and CH4 emissions from a silage corn (Zea mays L.) (2013)-barley (Hordeum vulgare L.) (2014)-alfalfa (Medicago sativa L.) (2015) rotation under conventional tillage and sprinkler irrigation. We evaluated the effectiveness of an enhanced-efficiency fertilizer (SuperU, a stabilized granular urea with urease and nitrification inhibitors) to reduce N2O emissions compared with granular urea and to determine GHG emissions from fall-applied dairy manure or composted dairy manure and spring-applied dairy manure. Nitrogen was applied during the first 2 yr of the study. SuperU plots emitted 53% less N2O than urea with corn, whereas no emission reductions occurred in 2014 with barley. The N2O-N emission losses as a percentage of total N applied were 0.21 and 0.04% for urea and SuperU in 2013, respectively, with losses of 0.05% from both urea fertilizers in 2014. On average, N2O fluxes from fall and spring manure were statistically similar and greater than the other N treatments in 2014 and a lasting manure treatment effect on emissions occurred under alfalfa. Carbon dioxide fluxes were greatest from fall-and spring-applied manure during the first 2 yr. Methane fluxes were negative, indicating microbial oxidation, and no differences occurred among the treatments. Corn, barley, and alfalfa yields were similar among all N treatments. This work demonstrates that SuperU can reduce N-2 O emissions from irrigated cropping systems in the semiarid western United States without affecting yields.