According to the organic dairy farmers the management and the diet composition on their farms differs that much from a conventional dairy farm that an exception to the currently applied standards of N and P excretion can be justified. The more extensive nature of the management, the slowly digestible feed, the lower protein levels in grass, the smaller proportion of concentrates, etc.. are all factors warranting such an exception. With this project, the N and P excretions from cows being fed organic diets, will be determined as precisely as possible and compared with that of the conventional dairy farming, taking, as far as possible, into account the specific characteristics of organic dairy farming. The methodology to derive these excretions will be as comparable as possible as to that used for deriving the excretions of conventional dairy farming. The excretions will be derived, on the one hand from theoretical calculations (based on data from the organic dairy sector) and on the other hand from balance and feeding trials with cows being fed organic diets, and from validation trials on 3 organic farms.