Fertiliser induced nitrous oxide emissions during energy crop cultivation on loamy sand soils

Nitrous oxide (N2O) fluxes from a loamy sand soil have been collected at an experimental field since 1999. To study the nitrogen (N) fertiliser induced emissions, annual crops and perennial plants received three different levels of N fertilisation: 0, 75, and 150 kg N ha−1. N2O was measured by gas chromatography and closed chamber technique. Water content of the soil was determined gravimetrically and the soil content of mineral N by ion chromatography. The N2O fluxes were below 30 μg N2O m−2 h−1 during the winter season and varied from 10 to more than 1000 μg N2O m−2 h−1 in the course of the vegetation season. N2O emissions after N fertilisation were assigned to fertiliser induced emissions. High N2O emissions at the end of the vegetation period are the result of increased mineralisation of soil organic matter. N2O emissions from freeze–thaw cycles gave only a small contribution to the total annual N2O emission budget from all blocks studied. Since the mean soil moisture content is very low (10%) and the water-filled pore space (WFPS) correlates negatively with N2O emissions, nitrification is considered the main source for N2O emissions. Evaluation of the data regarding dependence on fertilisation level indicates that N2O fluxes are positively correlated to soil NO3-N content. The N2O fluxes from annual crop plots are higher than those from plots with perennial plants (grass, willow, poplar). The mean N2O-N emission factor for fertiliser induced emissions from tilled soil is 1.0% in contrast to that of non-tilled soil with 0.7%. The mean fertiliser induced N2O-N emissions, averaged over all crops and the total period of nine years, are in the range of 0.8 ± 0.2% of the N fertiliser applied.