Post-harvest N2O and CO2 emissions related to plant residue incorporation of oilseed rape and barley straw depend on soil NO3- content

Abstract The sustainable production of bioenergy from crops like oilseed rape, barley, and maize presents a significant option to mitigate climate change by reducing fossil CO 2 emissions. Greenhouse gas emissions (specifically N 2 O) during the energy crop production need to be quantified precisely for reliable life cycle analysis of bioenergy cropping systems. Energy crops (specifically oilseed rape) have a very high N demand, which results in a higher N-fertilizer application and thus higher risk of N 2 O emissions not only during the vegetation period but also after crop harvest due to i) incorporation of N rich plant residue to soil and/or ii) residual N. An incubation experiment was conducted under conditions favoring denitrification (80% water-holding capacity), to study the drivers of N 2 O emissions specifically during the post-harvest period. Here we compared two different plant residues varying in C/N ratio (oilseed rape (RST) and barley straw (BST)) with or without N supply and measured CO 2 , and N 2 O emissions. Stable isotope labeling ( 15 N) was used to quantify soil- and residue-born N 2 O. Incorporation of both plant residues alone induced significant increases in CO 2 emissions compared to control soil without straw addition (p  2 emissions was less pronounced when straw was incorporated in conjunction with mineral N. There was a clear increase in cumulative N 2 O emissions (p  2 O emissions was drastic when mineral N was added (15- and 23-fold). No significant differences in N 2 O emission were observed when comparing residue types (p > .05). Stable isotope labeling of barley straw clearly showed that the share of residue-born N 2 O was very low (1.35 or 0.4%) in the overall N 2 O fluxes in BST and BST + N. The present study suggests that N fertilization in autumn should be avoided to minimize N 2 O fluxes regardless of type of straw.