Effect Of Three N Fertilizers On Denitrification Rate Under Potato Crop.

Large inputs of nitrogen (N) are required to optimize yield and quality of potato and may result in a high potential for N losses including N₂O emissions. This three-year study compared the effect of three N fertilizers [ammonium nitrate (AN), ammonium sulphate (AS) and polymer coated urea (ESN)] and an unfertilized control (N₀) on denitrification rate (DR) from irrigated potato production on a light-textured soil in eastern Canada. Fertilizers were banded at the rate of 200 kg N ha^-1 (N₂₀₀). The ESN was applied all at-planting and AN and AS were split 40% at-planting and 60% at-hilling. The DR was measured biweekly from planting to harvest at two positions (hill-furrow) using the acetylene blockage technique. Average DR decreased from 2010-2012 (2.99, 1.68, and 0.76 µg N₂O-N kg dry soil^-1 d^-1) related to intensive water inputs (>20 mm) occurring 24-72 hours before measurement. Yearly, DR varied significantly over the sampling date mainly related to water inputs. In 2011 and 2012, DR were significantly higher with N₂₀₀ (2.11 and 0.92 µg N₂O-N kg dry soil^-1 d^-1) than N₀ (0.76 and 0.37 µg N₂O-N kg dry soil^-1 d^-1). In 2011, a significant interaction between N fertilizers and positions was observed. The DR measured in the hill varied among treatments (N₀<AS<AN<ESN) whereas N treatment had no significant effect on DR measured in the furrow. Only ESN DR was significantly lower in the furrow compared with the hill (0.71 vs 3.65 µg N₂O-N kg dry soil^-1 d^-1). There was a significant position by sampling date interaction on DR in 2011, however, the DR pattern was inconsistent between hill and furrow within the growing season and from one year to the next. Our results confirm that N fertilizers can influence DR, but these effects are modulated by environmental factors, including climatic conditions and cultural practices.