Effects of effluent and urea application on groundwater, soil and pastures at WTARS

Abstract

encouraged by many regional councils, and the use of urea fertiliser on dairy farms has increased over recent years. A 3-year trial was started in September 1997 to investigate the effects of urea and dairy effluent applications on pastures, soils and groundwater quality. Twenty-one 0.25 ha paddocks received urea or dairy effluent at rates of 0, 100, 200, or 400 kg N/ha/yr, and were grazed by dairy cows. Increasing nitrogen application rates resulted in increased pasture production and ryegrass content, and nitrate leaching to ground water. Nitrate leaching was estimated to be 14, 18, 26 and 56 kg N/ha/yr for the 0, 100, 200 and 400 kg N/ha/yr application rates respectively. No differences in these responses were measured between urea and effluent when applied at the same rate of nitrogen. Application of dairy effluent resulted in increased average pasture potassium levels from 3.65%DM to 4.00%DM, which may have implications for animal health. Application of dairy effluent also decreased soil sulphur levels and increased soil magnesium status. Keywords: dairy effluent, groundwater, nitrate leaching, nitrogen, pasture, soil, urea