In Germany now all farms with more than 20 hectares or 50 large livestock units (50 cow) or more than 750 kilogram supplied nitrogen are required to do mineral bookkeeping. It concerns the supply and removal of nitrogen and phosphorus, for example via feed, milk, animals and fertilizer. When buying additional feed, the N and P quantities must be taken into account and documented. Another important flow of nutrients results from the purchase and sale of animals. In dairy farms the nitrogen and phosphorus in the milk sold must also be balanced