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In the past, environmental Phosphorus (P) parameters like soil P indices have been used to catogorize the potential risk of P losses from agricultural land. In order to assess the actual risk of P pollution of groundwater and surface waters, dynamic process oriented soil and water quality models have been frequently used. Recently, an approximating model for phosphorus, called SIMPLE, has been developed. This model approximates the output from a complex dynamic water quality model. The approximating model is called a metamodel. This simple P-model proves to be a powerful tool for quick assessment of the risk of P pollution from agricultural land to surface waters.

The increased input of fertilizers and animal wastes after 1950 has boosted agricultural crop production to a high level in many industrialized countries, but it has also contributed to increased nitrogen and phosphorus emissions from agriculture to groundwaters and surface waters. This paper summarizes the pathways and controls of nitrogen and phosphorus losses to surface waters, and it presents estimates andpredictions of the losses from agricultural soils in The Netherlandsinto surface waters, before and after the implementation of policiesand measures to reduce nutrient losses from agriculture. Implementation of the nutrient accounting system MINAS, aiming at a step-wise lowering of nitrogen and phosphorus surpluses at farm level, will decrease the total nitrogen and phosphorus surpluses between the years 1985 and 2008 by 58 and 82%, respectively. These large decreases are theresult of a strong decrease in the input via fertilizers and animal wastes, combined with only a minor decrease in the output via harvested products. Nitrogen emissions from agricultural land to surface waters will decrease by 38% between 1985 and 2008. Phosphorus emissions from agricultural land to surface waters are expected not to decreaseon the short term. [ABSTRACT FROM AUTHOR]

Nitrate concentrations in groundwater are correlated with the nitrogen surpluses at the soil surface. In the Netherlands, both nitrogen surpluses of agricultural land and nitrate concentrations in the groundwater of sandy soils are high. At present, nitrate concentrations inthe groundwater of sandy soils exceed the 1980 EC Directive on the Quality of Water Intended for Human Consumption by a factor of 1 to 5.This paper discusses the effects of a series of policies and measures launched by the Dutch government from 1986 onwards to decrease nitrogen losses to acceptable levels. Main focus is on the nitrogen and phosphorus accounting system MINAS, which will be implemented from 1998 onwards. The possible effects of the MINAS policy and measures on the nitrate contamination of groundwater have been examined via whole-farm analyses and simulation models, with a main focus on the nitrateleaky sandy soils and dairy farming systems. With MINAS, all farmershave to account for the nitrogen and phosphorus that is entering andleaving the farm. Further, MINAS includes charged and levy-free surpluses. The height of charges and the height of the levy-free surpluses together regulate the actual nitrogen surpluses at the farms. Levy-free nitrogen surpluses will be lowered step-wise to 100 kg for arable land and 180 kg per ha for grassland in 2008. Following the implementation of the series of policy measures in the late eighties, data statistics indicate that the nitrogen surplus decreased from a mean of347 kg per ha agricultural land 1985 to a mean of 299 kg per ha in 1995. Following the implementation of MINAS, our model predictions indicate that the nitrogen surplus at farm level will decrease further to a mean of 147 kg per ha in 2008, i.e. a reduction of 58% with reference to 1985. Mean nitrate concentrations at the average lowest groundwater level will decrease by 60%. Ultimately, 12% of the agricultural land (on sandy soils) will still have a nitrate concentration in the grou [ABSTRACT FROM AUTHOR]