Nitrous oxide emissions under different soil and land management conditions

Nitrous oxide (N2O) emissions of three different soils -- a rendzina on cryoturbed soil, a hydromorphic leached brown soil and a superficial soil on a calcareous plateau -- were measured using the chamber method. Each site included four types of land management: bare soil, seeded unfertilized soil, a suboptimally fertilized rapeseed crop and an overfertilized rapeseed crop. Fluxes varied from -1 g to 100 g N2O-nitrogen ha-1 day-1. The highest rates of N2O emissions were measured during spring on the hydromorphic leached brown soil which had been fertilized with nitrogen (N); the total emissions during a 5-month period exceeded 3500 g N ha-1. Significant fluxes were also observed during the summer. Very marked effects of soil type and management were observed. Two factors -- the soil hydraulic behaviour and the ability of the microbial population to reduce N2O -- appear to be essential in determining emissions of N2O by soils. In fact, the hydromorphic leached brown soil showed the highest emissions, despite having the lowest denitrification potential because of its water-filled pore space and low N2O reductase activity. Soil management also appears to affect both soil nitrate content and N2O emissions.