Nitrous oxide release from arable soil: Importance of N-fertilization, crops and temporal variation

Throughout 33 months nitrous oxide (N2O) release rates were measured from a field experiment comparing crop and N-fertilization treatments laid out on a luvisol derived from loess. Winter wheat, winter barley, winter rape and sugar beet were cultivated using conventional soil management. 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 obtained were correlated with physical and chemical soil properties as well as with climatic and plant production data. Large temporal changes were found in the N2O emission rates. The data were approximately log-normal distributed. 50% of the annual N2O emissions were found during winter (October to February), which resulted from both physical release of subsurface-produced N2O during soil freezing and microbial N2O production during daily thawing and freezing cycles. The total N2O losses during the winter increased with decreasing dry matter-to-N-content ratio of the plant residues incorporated into the soil by ploughing (r=−0.56, P≤0.001). The crop species had a significant influence on the N2O emissions. The relative N2O losses from the applied N-fertilizer ranged between 0.7% and 4.1%. While the lowest losses were found for winter wheat, the highest losses were found for sugar beet, which received the smallest amount of N-fertilizer. The linear 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 potential of the soil investigated.