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 u nfertilized soil, a suboptimally fertilized rapeseed crop and an overf ertilized rapeseed crop. Fluxes varied from -1 g to 100 g N2O-nitrogen ha(-1) day(-1). The highest rates of N2O emissions were measured duri ng spring on the hydromorphic leached brown soil which had been fertil ized with nitrogen (N); the total emissions during a 5-month period ex ceeded 3500 g N ha(-1). Significant fluxes were also observed during t he summer. Very marked effects of soil type and management were observ ed. Two factors - the soil hydraulic behaviour and the ability of the microbial population to reduce N2O - appear to be essential in determi ning emissions of N2O by soils. In fact, the hydromorphic leached brow n soil showed the highest emissions, despite having the lowest denitri fication potential because of its water-filled pore space and low N2O reductase activity. Soil management also appears to affect both soil n itrate content and N2O emissions.