Nitrous oxide fluxes from maize fields: Relationship to yield, site-specific fertilization, and soil conditions

Nitrous oxide emissions and selected soil properties in a high and a low yielding area of a maize field were monitored weekly over a 1-year period. In both the high and the low yielding area, N₂O emissions from a treatment subject to site-specific N-fertilization were compared to a conventionally fertilized control. Emission peaks were measured following N fertilization, rainfall, harvest, tillage and freeze-thaw cycles from all treatments in conditions favorable for denitrification. Between 80 and 90% of annual emissions were released between April and September. A value of 60% WFPS was identified as a threshold for the induction of elevated N₂O emissions (>50 μg N₂O-N m^-2 h^-1). A significant relationship (r² = 0.41) between N₂O flux rates and WFPS was found when neither soil nitrate contents nor temperature were limiting for microbial denitrification. Mean cumulative N₂O emissions from the control treatments in the high yielding area, located in a footslope position and thus receiving lateral water and nutrient supply, more than doubled those from the control treatments in the low yielding area in a shoulder position (8.7 and 3.9 kg N₂O-N ha^-1, respectively). Higher average WFPS in the high yielding area was identified as responsible for this difference. The site-specific fertilized treatments in the low yielding area were supplied with 125 kg N fertilizer ha^-1 as compared to 150 kg N fertilizer ha^-1 (control treatments). This reduction resulted in 34% less N₂O released in roughly 10 months following differentiated fertilization while crop yield remained the same. In the high yielding area, N fertilizer supply in the site-specific fertilized treatment was 175 kg N ha^-1 as compared to 150 kg N ha^-1 in the control. Neither crop yield nor N₂O emissions were significantly affected by the different fertilizer rates.