Fate of nitrogen in dairy factory effluent irrigated onto land

Abstract

Abstract It is important to ensure that the irrigation of dairy factory effluent (DFE) onto farmland does not cause adverse effects on the wider environment, e.g., nitrate leaching and groundwater contamination, or significant emissions of nitrous oxide (N 2 O), which is a greenhouse and ozone‐depleting gas. The aim of this project was to determine the fate of nitrogen (N) from DFE applied on land. Nitrogen removals or losses by plant uptake, leaching, denitrification, volatilisation, and immobilisation were quantified on undisturbed soil lysimeters and in field studies. The soil was Templeton fine sandy loam (Typic Haplustept) and the pasture was a mixture of perennial ryegrass (Lolium perenne) and white clover (Trifolium repens) . The results showed that when DFE was applied at 300 or 600 kg N ha –1 yr –1 , 3.7–51.4% was taken up by the pasture, 0.2–0.3% was leached, 8.4–12.2% was lost by denitrification, 51.6–63.6% was recovered in the soil organic N, and <1% was lost by volatilisation. The high amount of N immobilised was probably due to the high soluble organic carbon content of the DFE (i.e., lactose). Immobilisation was probably also responsible for the relatively low nitrate leaching losses. However, the leaching losses were higher under grazed than under cut and carry systems. There is a need to study the long‐term fate of N from DFE that is immobilised in the soil.