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.