Split Application of Urea Does Not Decrease and May Increase Nitrous Oxide Emissions in Rainfed Corn

Abstract

Modification of N fertilizer application timing within the growing season has the potential to reduce soil nitrous oxide (N2O) emissions but limited data are available to assess its effects. We compared cumulative growing season nitrous oxide emissions (cN2O) following urea applied to corn (Zea mays L.) in a single application (SA) at planting or in three split applications (SpA) over the growing season. For both SA and SpA, granular urea was broadcast and incorporated at six fertilizer N rates in the corn phase of a corn–soybean [Glycine max (L.) Merr.] rotation and in a continuous corn system over two growing seasons. Daily N2O flux was measured using chambers on 35 dates in 2012 and 40 dates in 2013 and soil nitrate‐N concentration was measured weekly. Split application did not affect grain yield and did not reduce cN2O. Across N rates and rotations, cN2O was 55% greater with SpA compared with SA in 2012. Increased cN2O with SpA in 2012 likely resulted from a prolonged dry period before the second split application followed by large rainfall events following the third split application. Across years and rotations, SpA increased cN2O by 57% compared with SA when the maximum N rate was applied. Exponential relationships between cN2O and fertilizer N rate explained 62 to 74% of the variance in area‐based cN2O and 54% of the variance in yield‐based cN2O. Applying urea to coincide with periods of high crop N demand does not necessarily reduce and may increase N2O emissions.