Soil Nitrous Oxide Emissions from an Irrigated Rotational Cropping System As Affected By Nitrogen Source.

Little information is available regarding the effects of fertilizer and manure inputs on nitrous oxide (N₂O) emissions from irrigated semiarid soils. In this cropping study conducted in south-central Idaho, we report N₂O emissions from a silage corn-barley-alfalfa rotation. The treatments were: i) no fertilizer [control]; ii) granular urea; iii) SuperU [stabilized urea source with urease and nitrification inhibitors]; iv) composted dairy manure applied in the fall and granular urea applied in the spring; v) dairy manure applied in the fall; and vi) dairy manure applied in the spring. The experimental design was a randomized complete block with four replications. Fertilizers were applied at agronomic rates based on soil nitrogen test data, while compost and manure were added at rates typical of this region. Nitrous oxide measurements were conducted in 2013 (corn), 2014 (barley) and 2015 (alfalfa) using a vented, non-steady-state, closed chamber technique. Under corn production, average cumulative N₂O emissions (kg N₂O/ha) from urea (0.92), compost+urea (1.0), and spring manure (0.84) were similar and significantly greater (P < 0.001) than the control (0.32). Under barley, N₂O emissions from fall (2.4) and spring (2.3) manure were greater (P < 0.001) than the control (0.62), which was not different than urea (0.68), SuperU (0.68), and compost+urea (0.81). While no nitrogen sources were applied to alfalfa in 2015, cumulative N₂O emissions were significantly greater (P < 0.005) from the fall (1.5) and spring (1.3) manure plots than the control (0.57). Compared with granular urea, SuperU reduced N₂O emissions by 52% in corn and 0% in barley and alfalfa. There was also no nitrogen source effect on corn, barley, and alfalfa yields. This work demonstrates that enhanced-efficiency nitrogen fertilizers, such as SuperU, can potentially reduce N₂O emissions from irrigated cropping systems while not reducing crop yields.