N2O and NO emissions by agricultural soils with low hydraulic potentials

N2O and NO production were studied on five agricultural soils with low hydraulic potentials. All experiments were performed in a laboratory under standard incubation conditions to limit any intrinsic soil heterogeneity. The mechanisms involved in NO and N2O production was investigated using the inhibitory properties of acetylene on nitrification and N2O reduction. This work confirmed that N2O and NO could be produced by soils under aerobic conditions. Nitrification seemed to be the only process involved in NO production and the main process involved in N2O production by the five studied soils when the water content was low. Nevertheless, aerobic denitrification with N2O release was observed in one soil. The proportion of N emitted as NO and N2O through nitrification varied considerably from soil to soil and, in some soils, also varied with soil hydraulic potential, ranging from 0 to 2.5%, and from 0.03 to 1%, respectively. This study clearly shows that both NO emission and the gaseous N emitted in aerated conditions should be taken into account in determining the N-budget on cultivated soils.