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 100kgha^–1year^–1), N-200 (urea-N at 200kgha^–1year^–1), FYM-16 (farmyard manure at 16 tonnes ha^–1year^–1), FYM-32 (farmyard manure at 32 tonnesha^–1year^–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 (83gNha^–1day^–1), followed by FYM-32 (60gNha^–1day^–1, N-100 (51gNha^–1day^–1), FYM-16 (47gNha^–1day^–1) and the control (33gNha^–1 day^–1). During the maize growing season, average denitrification rate was highest in FYM-32 (525gNha^–1day^–1), followed by FYM-16 (408gNha^–1day^–1), N-200 (372gNha^–1day^–1, N-100 (262gNha^–1day^–1) and the control (203gNha^–1day^–1). Denitrification loss integrated over the whole vegetation period was at a maximum under FYM-32 (13.9kgNha^–1), followed by N-200 (11.8kgNha^–1), FYM-16 (10.6kgNha^–1) and N-100 (8.0kgNha^–1), whereas the minimum was observed for the control (5.8kgNha^–1). Under both crops, denitrification was significantly correlated with water-filled pore space and soil NO₃ ^–-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 100–200kgNha^–1year^–1. Received: 14 January 1997