Effects of changing land use in the Netherlands on net carbon fixation

For three land use systems, arable land, grassland and forest, average carbon flows and car­ bon pools in the Netherlands have been determined. For harvested products data are avail­ able from statistics and they were used as a basis for calculating the carbon flows. Average carbon pools, particularly in the soil, cannot be derived directly. For the calculation of this carbon pool a method has been applied that requires only three input data: the average amount of crop or tree residues, the decomposition rate of soil organic matter and the so­ called humification coefficient. For broad studies this simple method can particularly be use­ ful. However, this method can only be applied to situations in equilibrium, where the rates of incorporation of crop residues or tree litter and decomposition of soil organic matter are just equal and hence, the soil carbon is constant. In the soil, a state of equilibrium may not really occur, as continually changes in crop rotation and land use will take place. For a changing land use and hence a changing rate of incorporation of organic material it is shown how the new state of equilibrium and the rate of change in carbon pool size can be calculated. For a number of actual changes in land use in the Netherlands the resulting changes in carbon pool sizes were determined.