Soil N2O Emissions from Recovered Organic Waste Application in Versailles Plain (France): A Laboratory Approach

Within the framework of the French Gessol3 programme (Prostock) we sought to characterize the emissions of nitrous oxide (N 2 O) from organic wastes applied on the Versailles plain in relation with the main soil types of this area. Four different soils with contrasting textures as well as four organic waste products used to fertilize crops were selected. N 2 O and CO 2 flux measurements were estimated during 13 days after application of the various types of Exogenous Organic Matter (EOM) by using a laboratory setup with soil columns prepared by combining the different types of soil and the EOM treatments. Soil columns were prepared by homogeneously adding the various waste products to provide an equivalent of 4 t C org ha −1 of input. They were maintained at their maximum water holding capacities. Hydraulic potentials of soil-cylinder in relation to soil water contents were also characterized. Two EOMs were very labile while the other two were much more stable. Three days after treatment, N 2 O fluxes were negligible for the EOMs with a weak mineralization rate. Only the initial mineral nitrogen content of these two wastes contributed to the emissions. However, for the two labile products the C/N ratios were very different (6 and 38). This led to a non-significant production of NH 4 + during the mineralization and weak N 2 O fluxes for the product with a high C/N ratio. Concerning the EOM with a high mineralization rate and low C/N ratio, large NH 4 + amounts were released during the mineralization of the EOM, leading, for all four soils, to a slowing down of the nitrification rate and of N 2 O emissions. These slowdowns were even more pronounced when the Cation Exchange Capacity (CEC) and pH of the soils were low. Nitrous oxide emissions were found to be greater for soils with higher clay contents. Clay soils have a higher water holding capacity and, due to the buffering effect of their CEC, they can maintain an active nitrification rate with high soil NH 4 + contents. For CO 2 and N 2 O flux magnitudes, soil properties were as important as the EOM characteristics.