Split application of urea does not decrease and may increase nitrous oxide emissions in rainfed corn

Authors: Venterea, Rodney - Rod; COULTER, JEFFREY - UNIVERSITY OF MINNESOTA

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/1/2014
Publication Date: 1/13/2015
Publication URL: http://handle.nal.usda.gov/10113/60457
Citation: Venterea, R.T., Coulter, J.A. 2015. Split application of urea does not decrease and may increase nitrous oxide emissions in rainfed corn. Agronomy Journal. 107(1):337-348.

Interpretive Summary: Modification of nitrogen (N) management practices to reduce emissions of nitrous oxide (N2O) has been identified as a strategy for reducing the greenhouse gas footprint of agricultural cropping systems. Altering the timing of N fertilizer application is frequently mentioned as a potentially effective practice for reducing all forms of reactive N loss from fertilized soil including N2O. However, a limited number of studies have measured effects of altered N fertilizer application timing within the growing season on soil N2O emissions and the results have not been consistent. We compared cumulative growing season N2O emissions (cN2O) following urea applied to corn in a single application at planting or in three split applications over the growing season. Each timing treatment was applied at six fertilizer N rates in the corn phase of a corn-soybean 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 of fertilizer N did not affect grain yield and did not reduce cN2O. Across N rates and crop rotations, cN2O was 55% greater with split compared with single application in 2012. Increased cN2O with split application in 2012 likely resulted from a prolonged dry period prior to the second split application followed by large rainfall events following the third split application. Across years and crop rotations, split application increased cN2O by 57% compared with single application when the maximum N rate was applied. Applying N fertilizer to coincide with periods of high crop N demand does not necessarily reduce and may increase N2O emissions. These results will be of interest to scientists, land managers and policy makers interested in identifying effective strategies to reduce N2O emissions.

Technical Abstract: Modification of nitrogen (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 N2O 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. Each timing treatment was applied 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 (dN2O) was measured using chambers on 35 dates in 2012 and 40 dates in 2013 and soil nitrate-N concentration (SN) was measured weekly. Split application of fertilizer N did not affect grain yield and did not reduce cN2O. Across N rates and crop 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 prior to the second split application followed by large rainfall events following the third split application. Across years and crop 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 N fertilizer to coincide with periods of high crop N demand does not necessarily reduce and may increase N2O emissions.