Long-term studies on greenhouse gas fluxes during cultivation of energy crops on sandy soils

The emission of nitrous oxide (N2O) from the soil has a significant impact on the greenhouse gas balance of energy crops. The intensity of nitrogen fertilising affects the source strength of N2O emissions and methane oxidation in the soil. These trace gas fluxes were measured using the flux chamber method in combination with gas chromatography. The mean annually accumulated emission of N2O-N was 1.1 kg N2O-N ha−1 yr−1 ranging from 0.4 to 5.2 kg N2O-N ha−1 yr−1. Sandy soil fertilisation generally led to low N2O-N emissions, ranging from 0.2% to 0.7% of the applied nitrogen. Both, precipitation and temperature significantly influenced the total emission of N2O. The change from dry weather in 1999 to more humid weather in 2000 and 2001 resulted in enhanced N2O emissions. Enhanced N2O emission was also observed due to nitrogen fertilisation, soil cultivation processes and freeze–thaw cycles. Additionally, there were a few comparatively high local N2O emissions with peak values of 900 μg N2O-N m−2 h−1. Methane (CH4) uptake has a clear relationship with soil temperature, having minimum values during the winter and maximum values during the summer. Increasing precipitation significantly reduces the methane uptake by the soil. Non-fertilised plots showed a higher reduction in CH4 uptake due to increasing precipitation than fertilised plots. In sandy soils the mean annually accumulated CH4 uptake varied from 0.36 kg CH4 ha−1 yr−1 (2001) to 0.68 kg CH4 ha−1 yr−1 (1999). With regard to the greenhouse gas balance of energy crops, the low uptake of methane compensates for only 1% of the CO2 equivalent of the N-fertiliser-induced N2O emissions.