Effects of combinations of land use history and nitrogen application on nitrate concentration in the groundwater

Effects of differences in both land use history and levels of nitrogen (N) application on nitrate concentration in the groundwater were studied for permanent pastures located on a single soil series in the Frisian Woodlands in the north of the Netherlands. The study was carried out for three fields: A, B and C. Field A was an old pasture, field B was a reseeded pasture and field C had been previously used for growing silage maize. The models SWAP and ANIMO were used for long-term simulations of the soil organic matter and soil N dynamics. The soil data from fields A, B and C were combined with different N application levels derived from commercial dairy farms on the same soil series for 2000. Soil organic matter and soil organic N were lower in field C than in fields A and B. In field C also the probability of exceeding the environmental threshold for nitrate in groundwater of 50 mg l–1 was lowest, which was ascribed to net immobilization irrespective of the high levels of N applied. However, this probability increased rapidly when the soil properties were similar to those of the old pasture (field A). Simulated levels of N uptake were higher for field A than for fields B and C at all levels of N applied. On old pasture, reducing N application levels can lower the probability of exceeding the environmental threshold for nitrate by up to 20% whilst hardly affecting N uptake.