Cropland soil nitrogen oxide emissions vary with dairy manure incorporation methods

Abstract

Soils contribute 15%–75% of total atmospheric nitrogen oxide (NO_x) emissions in agricultural regions during the growing season. However, the impacts of cropland fertilizer management on spatially heterogeneous, temporally episodic NO_x emission patterns are highly uncertain. We examine the effects of liquid slurry dairy manure application practices on soil NO_x emissions in rainfed, corn-soybean rotations during spring 2016 and 2017. Daily soil NO_x emissions and weekly soil inorganic N measurements were performed in a randomized split–split plot design for 1–4 weeks following manure applications. NO_x emissions and soil N with shallow-disk injection and chisel-disk manure incorporation methods were compared with unincorporated broadcast practices. Injected manure and chisel-disk incorporation exhibited two–four times larger mean NO_x emissions than those with unincorporated broadcast manure. Larger soil NO_x emissions with manure incorporation practices were driven by the predominance of nitrification in these treatments with evidence of soil nitrate production. Soil NO_x emission differences between treatments were detectable across order of magnitude changes in daily NO_x emissions during two growing seasons. Larger soil NO_x emissions associated with manure incorporation practices compared with unincorporated broadcast practices occur alongside larger N₂O and smaller NH₃ emissions, highlighting important air quality and climate impact tradeoffs for cropland manure fertilizer management choices.