Extraction of soil with CaC1, has been recommended as a measure of bioavailability of heavy metals. Interpretation of soil extraction data in terms of plant uptake potential may improve when the chemical behaviour of heavy metals in these extracts is ascertained. The effect of pH, Cd complexation by C1, and competition between Cd and Ca on Cd sorption was studied at an ionic strength of 0.03 M. Sorption of cadmium was measured in 0.01 M CaCI,, in 0.01 M Ca(NO,),, in a mixture of 0.02 M NaCl and 0.01 M NaNO,, and in 0.03 M NaNO,, at different values of pH ranging from 3.8 to 4.9. Adsorption isotherms were all linear, with a negative intercept on the y-axis. This intercept indicated (linear) desorption

On average, crops require about 30 kg ha-' y-' of P in humid regions. In some regions fertilizer and manure are applied in amounts that exceed this. The surplus of P in agricultural areas is about kg ha-' y-'. This implies an accumulation of P. The surplus of P estimated from the balance of agricultural soils of industrialized countries in Europe in the last four decades is between 800 and more than 1500 kg ha-' although this distribution is not even. Phosphorus accumulation is more than one order of magnitude higher than average in areas with intensive livestock farming. Consequently, the application of high levels of manure exceed the capacity of the soil to store P. This implies that P saturation may pose a problem. Indeed, about half of the Dutch sandy soils (approximately 300000 ha) are currently considered to be saturated with P, meaning that there is a hazard of P leaching to groundwaters in the future.Assuming current phosphate application rates, phosphate leaching is a distinct possibility over a period of decades to a century. Vulnerable areas are soils with high inputs, low sorption capacities for P, high water-tables and a low retention time for water. The possible consequence is a time-delayed increase of eutrophication of surface waters (lakes, rivers and the sea) caused by a diffuse load of P in the few next decades. Modelling the influence of different agricultural strategies shows that accumulation of P would not increase further only if the use of P increases by an amount that compensates for the increased inputs. It is proposed to change the current support system of agriculture by installing a system of financial incentives and taxes which seek to promote nutrient balances for each farm. KEY WORDS Phosphorus accumulation saturation Soils Groundwaters EUTROPHICATION IN EUROPEEutrophication of surface waters and coastal seas caused by an increasing load of nutrients, especially phosphorus, is a problem throughout Europe and efforts are needed to reduce the nutrient inputs into the surface waters. Regional balances of nutrients in surface waters (Werner, et al., 1991;Behrendt, 1991) have shown that the current levels of eutrophication cannot be stopped by the reduction of point sources (communal and industrial sewage) alone. With regard to the diffuse sources, such balances are snapshots of the current situation and do not take into account long-term and time-delayed effects. The leaching of nitrates from agricultural soils to groundwater and then surface waters, which has received increasing attention in the last two decades, shows that ignorance of the long-term effects of the relatively high applications of fertilizers in Europe leads to considerable problems of human and environmental health. In general, an estimation of the diffuse loads to surface waters need to take previous developments into account. Possible scenarios, especially those caused by time-delayed responses, or chemical time bombs (CTBs) need to be modelled. According to Stigliani (1991), CTBs have been defined as pos...

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