NITROUS-OXIDE RELEASE FROM ARABLE SOIL - IMPORTANCE OF N-FERTILIZATION, CROPS AND TEMPORAL VARIATION

Throughout 33 months nitrous oxide (N2O) release rates were measured f rom a field experiment comparing crop and N-fertilization treatments l aid out on a luvisol derived from loess. Winter wheat, winter barley, winter rape and sugar beet were cultivated using conventional soil man agement. Each crop was fertilized at three rates of N application (N 1 .0: usual, N 0.5: 50% of usual, N 0.0: unfertilized). N2O losses obtai ned were correlated with physical and chemical soil properties as well as with climatic and plant production data. Large temporal changes we re found in the N2O emission rates. The data were approximately log-no rmal distributed. 50% of the annual N2O emissions were found during wi nter (October to February), which resulted From both physical release of subsurface-produced N2O during soil freezing and microbial N2O prod uction during daily thawing and freezing cycles. The total N2O losses during the winter increased with decreasing dry matter-to-N-content ra tio of the plant residues incorporated into the soil by ploughing (r = - 0.56, P less than or equal to 0.001). The crop species had a signif icant influence on the N2O emissions. The relative N2O losses from the applied N-fertilizer ranged between 0.7% and 4.1%. While the lowest l osses were found for winter wheat, the highest losses were found for s ugar beet, which received the smallest amount of N-fertilizer. The lin ear reduction of N-fertilization (N 1.0 to N 0.0) did not result in a linear decrease in N2O losses, reflecting the high N-mineralization po tential of the soil investigated. (C) 1998 Elsevier Science Ltd. All r ights reserved.