A new system of self-regulation mineral charges has been introduced on 1 January, 1998. In section 13af of the fertilizing Substances Act a basis has been laid for the method of calculation of such charges and this Decrees further elaborates the method of calculation insofar as the loss of animal-related nitrogen concerned. An additional correction regards the some substances ("strooisel") used for the keeping of animals. These substances, the use of which is encouraged, have a high nitrogen los