Lysimeter study of the fate of nutrients following subsurface injection and surface application of dairy pond sludge to pasture

The fate of nutrients in an organic waste (dairy pond sludge) was determined after surface application and subsurface injection into field plots on a free draining pasture soil. Soil monolith lysimeters were collected from the field plots and used to monitor plant uptake and leaching losses of nitrogen, phosphorus and potassium for 2 years following a single waste application, and for 1 year following two successive annual applications. Volatilisation losses of ammonia were low due to the low ammonium-nitrogen content of the waste and its near-neutral pH. Substantial nitrification occurred following waste injection. Nitrate leaching losses were low, even though nitrate accumulation following nitrification was high and macropore flow was a significant transport mechanism in this soil. The amount of nitrate leached was consistently higher following subsurface injection compared to surface application, although the concentration and amount lost in the drainage water was still relatively low, The low leaching losses were attributed to enhanced plant uptake of nutrients and possibly denitrification within the soil. Pasture plant production was increased by up to 40% following both methods of waste application.