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

Abstract

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.