Factors Affecting Nitrous Oxide Emission from a Sandy Grassland Soil under Controlled Field Conditions

Abstract

The atmospheric concentration of N 2 O currently rises by ~0.25% per year. Soils are the most important N 2 O sources. Many factors affect N 2 O emission from soils, via their influence on transport and nitrification and denitrification. The processes and factors determining N 2 O emission from a sandy grassland soil were studied in the Netherlands during the second half of 1993. Four grassland plots on sand (1.25 m x 1.25 m x 1 m) were intensively monitored with respect to fluxes from the soil and below-ground profiles of temperature, soil water potential, soil moisture content, N 2 O, CO 2, O 2 and several dissolved nutrients. Treatments were: height of groundwater table and amount of nitrate-N fertilizer. Initial results indicate that the relation between the mean N 2 O fluxes from soil and the nitrate-N fertilization rate exhibits a threshold phenomenon. Fluxes at 0 and 250 kg N/ha (in 5 equal dressing, 3-5 weeks apart) were similar. An application of 500 kg N/ha (in 5 equal dressings, 3-5 weeks apart), however, increased fluxes by a factor 4. No relation was found between N 2 O fluxes and below-ground N 2 O profiles in the upper soil layer. From the surface to the groundwater, the N 2 O concentrations first increased and then decreased with depth. Soil moisture content showed a similar profile.