Greenhouse Gas Emissions from an Irrigated Dairy Forage Rotation as Influenced by Fertilizer and Manure Applications
2017
Dungan, Robert S. | Leytem, April B. | Tarkalson, David D. | Ippolito, James A. | Bjorneberg, David L.
Core Ideas Urea formulated with urease and nitrification inhibitors can reduce N₂O emissions. Nitrous oxide‐N emission losses as a percentage of total N applied were ≤0.21%. Timing of manure application did not affect N₂O, CO₂, and CH₄ fluxes. Soil was a CH₄ sink and emissions were not influenced by N source. 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 N₂O emissions from irrigated cropping systems in the semiarid western United States without affecting yields.
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