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 ir rigated 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)), FY M-16 (farmyard manure at 16 tonnes ha(-1)year(-1)), FYM-32 (farmyard m anure at 32 tonnes ha(-1) year(-1)) and the control (unfertilized). Av eraged across sampling dates during the wheat season, the denitrificat ion rate as measured by the C2H2-inhibition/soil-core incubation metho d 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 (52 5 g Nh(-1) day(-1)), followed by FYM-16 (408g N ha(-1) day(-1)). N-200 (372g N ha(-1) day(-1) N-100 (262g N ha(-1) day(-1))) and the control (203 g N ha(-1) day(-1)). Denitrification loss integrated over the wh ole vegetation period was at a maximum under FYM-32 (13.9 kg N ha(-1)) , followed by (11.8 kg Na-1), FYM-16 (10.6kg N ha(-1)) and (8.0 kg N h a(-1)), whereas the minimum was observed for the control (5.8 kg N ha( -1)). Under both crops, denitrification was significantly correlated w ith water-filled pore space and soil NO3--N. The best multiple regress ion models accounted for 52% and 70% of the variability in denitrifica tion under wheat and maize, respectively. Results indicated that denit rification is not an important N loss mechanism in this well-drained, irrigated sandy-clay loam under a wheat-maize cropping system receivin g fer-P tilizer inputs in the range of 100-200 kg N ha(-1) year.