Nitrogen placement and source effects on nitrous oxide emissions and yields of irrigated corn.

Limited information is available on how N fertilizer placement affects soil nitrous oxide (NO) emissions under irrigated conditions in the semiarid western United States. Our objective was to compare surface banding near corn row and broadcasting of three N sources (urea, polymer-coated urea [PCU], and stabilized urea [SU] containing urease and nitrification inhibitors) on NO emissions from a clay loam soil under sprinkler-irrigated continuous corn production. The N fertilizers were applied at a rate of 202 kg N ha to strip-till (2010 and 2011) and no-till (2011) corn at crop emergence, with ∼19 mm irrigation water applied the next day. Band-applied N had a 1.46-fold greater NO emission than broadcast N averaged over N sources and three studies. Soil NO-N emissions from urea were 1.48- and 1.74-fold greater than from PCU and SU, respectively, when averaged over N placement and studies. The N placement × source interaction was not significant. Averaged across studies, grain yield and N uptake did not vary with N placement, whereas grain yields were greater for SU than PCU but were not different from urea. Nitrous oxide emissions per unit of N applied, per unit of grain yield, and per unit N uptake were 59, 49, and 47% greater, respectively, with banded than with broadcast N fertilizer. These studies show that N placement and N source selection are important manageable factors that can affect NO emissions and need to be considered when developing NO mitigation practices in irrigated cropping systems in the semiarid western United States.