Field Measurements of Gaseous Nitrogen Losses from an Alfisol planted with Sugar-Beets

To provide improved data for modelling gaseous N losses, denitrification measurements by the acetylene inhibition technique were conducted in an Alfisol cropped with sugar beets. This investigation is integrated into a research program designed to model water and nutrient fluxes in an agricultural water catchment area. During the cropping season (April–October) the influence of soil temperature, water, nitrate and available carbon on the release of nitrous oxide (N₂O) from the soil surface as well as on the N₂O-concentrations along the soil profile was studied. Denitrification increased with increasing soil temperature and water content. During the time of intensive plant growth denitrification was small. Both, field and laboratory studies revealed that denitrification began at temperatures between 5 and 8 °C and soil water contents above 30% (v/v). Available carbon did not seem to be a factor that limited denitrification under the prevailing climatic conditions. Assuming that the N₂O surface fluxes were representative of the amount of N denitrified, about 12 kg N ha^?1 was evolved during the cropping season. Spatial variability of N₂O evolution was, however, high and N₂O concentration in the soil profile was still high at the end of each 48 h sampling period.