Effect of crop-specific field management and N fertilization on N2O emissions from a fine-loamy soil

Agricultural soils are a major source of atmospheric N2O. This study was conducted to determine the effect of different crop-specific field management and N fertilization rates on N2O emissions from a fine-loamy Dystric Eutrochrept. Fluxes of N2O were measured for two years at least once a week on plots cropped with potatoes ( Solanum tuberosum) fertilized with 50 or 150 kg N ha(-1) a(-1), winterwheat (Triticum aestivum) fertilized with 90 or 180 kg N ha(-1) a(-1), corn (Zea mays) fertilized with 65 or 130 kg N ha(-1) a(-1), and on an unfertilized, set-aside soil planted with grass (mainly Lolium perenne and Festuca rubra). The mean N2O emission rate from the differently managed plots was closely correlated to the mean soil nitrate content in the Ap horizon for the cropping period (April to October, r(2) = 0.74), the winter period (November to March, r(2) = 0.93, one outlier excluded), and the whole year (r(2) = 0.81). N2O emissions outside the cropping period accounted for up to 58% of the annual emissions and were strongly affected by frost-thaw cycles. There was only a slight relationship between the amount of fertilizer N applied and the annual N2O emission (r(2) = 0.20). The mean annual N2O-N emission from the unfertilized set-aside soil was 0.29 kg ha(-1). The annual N2O-N emission from the fertilized crops for the low and the recommended rates of N fertilization were 1.34 and 2.41 kg ha(-1) for corn, 2.70 and 3.64 kg ha(-)1 for wheat, and 5.74 and 6.93 kg ha(-1) for potatoes. The high N2O emissions from potato plots were due to (i) high N2O losses from the interrow area during the cropping season and (ii) high soil nitrate contents after the potato harvest. The reduction of N fertilization (fertilizer was applied in spring and early summer) resulted in decreased N2O emissions during the cropping period. However, the emissions during the winter were not affected by the rate of N fertilization. The results show that the crop-specific field management had a great influence on the annual N2O emissions. It also affected the emissions per unit N fertilizer applied. The main reasons for this crop effect were crop-specific differences in soil nitrate and soil moisture content.