N2O Release During Cultivation of Energy Crops

Abstract

The emission of nitrous oxide (N 2 O) from the soil has a significant impact on the greenhouse gas balance of en- ergy crops. Factors like soil type, temperature, precipitation, tillage practice (annual or perennial crop), and level of fertilisation can affect the source strength of N2 O emissions and fertiliser-induced N2 O emissions. The N2 O-fluxes from different sites of an experimental field were measured using the flux chamber method in combi- nation with gas chromatography. The sites had three nitrogen fertilisation levels (0 kg N ha-1 y-1, 75 kg N ha-1 y-1, and 150 kg N ha-1 y-1). The soil nitrate concentration was determined by ion chromatography. The mean of an- nually accumulated emission of N2 O-N from all measuring spots was 1.4 kg N2 O-N ha-1 y-1. The accumulated emissions varied between 0.5 kg N2 O-N ha-1 y-1 to 3.8 kg N2 O-N ha-1 y-1 depending on fertilisation level, crop variety, and year. The mean annually fertiliser-induced N2 O-N emission from all fertilised sites was 0.7 % for the period from 1999 to 2004. This mean nitrogen conversion factor (ratio of N2 O-N emission to fertiliser-N in- put) ranged from 0.2 to 1.6 %. The mean conversion factor for perennial crops was lower (0.4 % for both fer- tilisation levels of 75 and 150 kg N ha-1 y-1) than that for annual crops (0.7 % for 75 kg N ha-1 y-1 and 0.9 % for 150 kg N ha-1 y-1). Several enhanced N2 O emission spots with maxima of up to 1400 μg N2O m-2 h-1 were ob- served at sites with the higher level of nitrogen fertilisation, lasting for several weeks, in the course of the meas- urements. These local peak emissions were mainly responsible for the raise of the nitrogen conversion factor of sites fertilised with 150 kg N ha-1 y-1 compared to sites with fertilisation level of 75 kg N ha-1 y-1. Although N2O emissions doubtless depend on nitrogen fertilisation and tillage, it could be shown that also climate has a strong effect on N2 O emissions. In contrast to a low correlation between N2 O emissions and soil nitrate concentration, N2 O emissions are relatively close correlated to annual precipitation.