Denitrification losses from an irrigated sandy-clay loam under a wheat-maize cropping system receiving different fertilizer treatments

Studies were conducted on denitrification in the plough layer of an irrigated sandy-clay loam under a wheat-maize cropping system receiving different fertilizer treatments. The treatments were: N-100 (urea-N at 100 kg ha-1 year-1), N-200 (urea-N at 200 kg ha-1 year-1), FYM-16 (farmyard manure at 16 tones ha-1 year-1), FYM-32 (farmyard manure at 32 tones ha-1 year-1 ) and the control (unfertilized). Averaged across sampling dates during the wheat season, the denitrification rate as measured by the C2H2-inhibition/soil-core incubation method was highest in N-200 (83 g N ha-1 day-1), followed by FYM-32 (60 g N ha-1 day-1, N-100 (51 g N ha-1 day-1), FYM-16 (47 g N ha-1 day-1) and the control (33 g N ha-1 day-1). During the maize growing season, average denitrification rate was highest in FYM-32 (525 g N ha-1 day-1),followed by FYM-16 (408 g N ha-1 day-1), N-200 (372 g N ha-1 day-1, N-100 (262 g N ha-1 day-1) and the control (203 g N ha-1 day-1). Denitrification loss integrated over the whole vegetation period was at a maximum under FYM-32 (13.9 kg N ha-1), followed by N-200 (11.8 kg N ha-1), FYM-l6 (l0.6 kg N ha-1) and N-100 (8.0 kg N ha-1), whereas the minimum was observed for the control (5.8 kg N ha-1). Under both crops, denitrification was significantly correlated with water-filled pore space and soil NO3(-1)-N. The best multiple regression models accounted for 52% and 70% of the variability in denitrification under wheat and maize, respectively. Results indicated that denitrification is not an important N loss mechanism in this well-drained, irrigated sandy-clay loam under a wheat-maize cropping system receiving fertilizer inputs in the range of 100-200 kg N ha-1 year-1.