Grassland management and nitrate leaching, a model approach

To calculate the effect of strategic, tactical and operational grassland management on nitrate leaching, the model Nitrogen, URinc and Pastures (NURP) was developed. Data were collected and relationships developed between (i) herbage production, herbage N content and fertilizer input, (ii) N utilization by cattle and N intake, (iii) soil mineral N accumulation and non-harvested N from fertilizers and urine, and (iv) soil mineral N and nitrate concentration in the upper groundwater. Validation of the model shows good agreement with measured data from farms and monitoring programmes. Calculations show that even on dry sandy soils nitrate concentrations of 50 mg 1-1 in the upper groundwater can be realized by a combination of restricted grazing during the growing season, housing earlier in the season and reduced fertilizer input. The effects of stocking rate, ratio dairy cows:young stock, milk production level, supplementary feeding, drought and urine scorch are discussed