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, N(2)O 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 N(2)O emissions (>50 mug N(2)O-N m(-2) h(-1)). A significant relationship (r(2) = 0.41) between N(2)O flux rates and WFPS was found when neither soil nitrate contents nor temperature were limiting for microbial denitrification. Mean cumulative N(2)O 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 N(2)O-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 N(2)O 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 N(2)O emissions were significantly affected by the different fertilizer rates. (C) 2003 Elsevier Science B.V. All rights reserved.