Another factor important in productivity is the availability of sufficient mineral nutrients, such as fixed nitrogen (N), phosphorus (P), sulphur (S), potassium (K), calcium (Ca) and magnesium (Mg). As to the indefinite availability of sufficient nutrients, difficulties may well emerge (Manley and Richardson 1995; Sims and Riddell-Black 1998; Perry 1998; Ranger and Turpault 1999; Pare et al. 2002). These partly follow from the limitations of natural processes involved in making minerals available to the generation of biomass. These are deposition on soil and weather­ing (Hedin et al. 2003). On a time scale valid for forestry and cropping, there is only a very small addition to total reserves of minerals that can be made avail­able to biomass due to geologic processes such as weathering (Ranger and Turpault 1999). Thus, the availability of nutrients from reserves generated by processes such as weathering may well go down over time on a time scale relevant to cropping and forestry due to losses linked to harvesting and erosion. External inputs of N and P in cropping and forestry are, moreover, dependent on the large-scale use of geochem­ically scarce natural resources (phosphate ore and fossil fuels) that are formed in slow geological processes, which does not allow for sustainable us. Fossil fuels are used to produce N-based synthetic fertilizers (Galloway et al. 2008). We will now first consider nutrients in forests and plantations and thereafter nutrients in arable soils.