Much of the N ingested by livestock is excreted; slurries from housed animals therefore represent substantial pools of N. Recycling through the soil-piant-animal system can reduce fertilizer usage, but current waste management practices often result in water or atmospheric pollution. This may occur directly, for example through contamination of water by a leaking slurry store, or indirectly through losses of plant nutrients, especially N, to the wider environment. The adverse effects of gaseous losses, from NH3, volatilisation and denitrification, and of nitrate leaching are becoming increasingly well recognised. Such losses also reduce the amounts of N available for uptake by plants and may account for low, variable crop responses to applied slurries. The objectives of this study are to quantify losses of N following application of slurries to land and to examine strategies for reduction, so conserving N for uptake by plants.

Following application of slurries to land, mainly grassland, N losses through NH3, volatilisation were measured by using small wind tunnels or micrometeorological techniques, through denitrification by a soil core incubation method with acetylene inhibition and through nitrate leaching in lysimeter experiments.