AMMONIA VOLATILISATION FROM IRRIGATED ACIDIC DAIRY PASTURES SOILS IN SOUTH-EAST AUSTRALIA

摘要

This paper reports ammonia emissions from irrigated, fertilized, acidic pastures soils grazed intensively by dairy cattle at DPI Kyabram, measured in summer and autumn using micrometrological techniques. The farming system is representative of dairy practice in south-east Australia. Irrigation bays are 65m x 365m and are grazed in rotation by 315 cows. After grazing for 2 to 3 days, the bays are fertilized with urea at 50kgN/ha and irrigated with 50mm of water. The regrowth period is about one month. Ammonia emissions were calculated through application of a Lagrangian model of atmospheric dispersion. Model inputs were ammonia concentrations on the boundaries of the bay, wind speed, wind direction, and atmospheric stability. Coefficients of variation for calculated fluxes were usually < 10%. Emissions from the pastures before grazing were negligible. Emissions from the whole herd during the grazing phases were 14.8 kg N in summer, but only 2.0 kg N in autumn, corresponding to emission factors of 12% and 1% for an assumed annual input of N in excreta of 150 kg N·cow~(-1)·yr~(-1). Only 1% of the urea-N was lost when irrigation followed fertilization immediately, but 6% was lost when irrigation was delayed for 3 days. The dispersion model appears to be a very useful tool for assessing gas emissions from agricultural operations.