Heavy-metal balances of agro-ecosystems in the Netherlands

Heavy-metal flows (Cd, Cu, Pb, and Zn) of arable, dairy and mixed farming systems in the Netherlands were studied, and farm-gate and field-scale balances calculated. On the field-scale, static and dynamic balances were distinguished. By determining the characteristic metal flows, it became possible to differentiate between farming systems and to select the most viable options for sustainable heavy-metal management. Crop rotation, and choice of fertilizers, clearly influenced the heavy-metal balance of arable farming systems. In dairy farming systems, the role of feed management was very important, but the effects on the heavy-metal balance were not always straightforward. Mixed farming systems compared favourably with specialized (arable or dairy) farming systems with regard to heavy-metal accumulation. Due to the internal cycling of feedstuff and manure, lower inputs were required and therefore the import of heavy-metal containing raw materials and products was minimized. Uncertainties related to the calculation of heavy-metal balances are discussed.