A stochastic empirical model for regional heavy-metal balances in agroecosystems.

Mass flux balancing provides essential information for preventive strategies against heavy-metal accumulation in agricultural soils that may result from atmospheric deposition and application of fertilizers and pesticides. In this paper we present the empirical stochastic balance model, PROTERRA-S, that estimates heavy-metal and phosphorus accumulation in agricultural soils on the regional level. The basic units of these balances are land use systems defined by livestock production and cultivated crops. The model is designed to use available databases, such as regional agricultural statistics and soil information systems. In a case study, we assessed the phosphorus, cadmium, and zinc balances for the Sundgau region, Switzerland. The regional P requirements of crops were mainly supplied by animal manure (56%) and commercial fertilizers (40%). Net cadmium fluxes of the land use systems ranged from 1.0 g ha(-1) yr(-1) (dairy and mixed farm types) to 17.8 g ha(-1) yr(-1) (animal husbandry systems), whereas the regional net cadmium flux was only 1.4 g ha(-1) yr(-1). The regional net zinc flux was 605 g ha(-1) yr(-1). The smallest net zinc flux of 101 g ha(-1) yr(-1) was found for an arable farm type, whereas for animal husbandry systems fluxes up to 39.8 kg ha(-1) yr(-1) were estimated. Comparison of model results with reported metal balances of experimental farms shows that identification of agricultural land with high risks of heavy-metal accumulation benefits from stratification of heavy-metal balances according to land use systems while accounting for their P fertilization plans. Consequently, the model may support sustainable management of heavy-metal cycles in agricultural soils.