Seasonal variation of N2O and CH4 fluxes in differently managed arable soils in southern Germany

Abstract

Agricultural practices are assumed to contribute significantly to the increase in atmospheric nitrous oxide (N 2 O) concentrations observed in the last decades, and they might influence the consumption of atmospheric methane (CH 4) by soil. The aim of this study was to quantify the effects of management intensity, soil type, and frost periods on the emission of N 2 O and the consumption of CH 4 in rotations in southern Germany. Fluxes of N 2 O and CH 4 were monitored over 12 months, using a closed chamber technique. The extensively managed system was cropped to sunflower and fertilized with farmyard manure (12 t ha−1). The intensively managed field was planted with spring wheat and fertilized with a total of 190 kg N ha−1 given as calcium ammonium nitrate (30 kg N) and urea‐NH 4 NO 3 solution (160 kg N). Variation in the N 2 O emissions with time was extremely high, with flux rates ranging from 0 to 2700 μg m−2 h−1. The N 2 O fluxes were influenced by soil properties, management practices, and weather. The highest release rates were measured in the winter during thawing of the frozen soil. During the growing season, N 2 O emission was highest after heavy precipitation. No strong relationship was found between N 2 O emission rates and soil factors such as soil temperature, soil moisture, and soil nitrate content. Annual fluxes of N 2 O from the extensively managed field were 9.4 and 12.9 kg N 2 O‐N ha−1 yr−1 for a sandy soil and a clay soil, respectively. Total N 2 O‐N losses from the intensively fertilized field amounted to 9.6 kg ha−1 yr−1 for a silty soil with a tendency to waterlogging during wintertime and to 16.8 kg ha yr−1 for a loamy colluvial soil. Up to 46% of the annual N 2 O evolution was emitted during December and January when frost/thaw cycles induced extremely high N 2 O production. The application of urea‐NH 4 NO 3 solution significantly increased N 2 O emission rates. Of the 160 kg N applied, 2.9 kg N or 1.8% was lost as N 2 O within a period of 8 weeks. Rates of CH 4‐C uptake varied from 0 to 17 μg m−2 h−1. Soil temperature correlated positively and soil moisture correlated negatively with the CH 4 consumption. Stepwise multiple linear regression, including these soil factors, explained up to 44% of the variation in CH 4 fluxes. Annual CH 4‐C uptake was rather similar for the intensively and extensively managed Eutrochrepts, ranging from 348 to 395 g ha−1. Significantly higher CH 4‐C consumption of 567 g ha−1 yr−1 occurred in the colluvial soil (Typic Udifluvent). N fertilizers had no effect on the CH 4 flux rates.