Nutrient management planning has become an important tool in an effort to improve water quality. In Wisconsin, nutrient management regulations are in the process of moving to a phosphorus (P) based standard. As such, P budgeting and the P index will greatly influence manure applications. Thus, there is a need to better understand how soil test P changes with respect to P based manure application.

In Wisconsin, only 60% of the total P applied in manure is considered to be available to the crop during the first year after application (i.e. relative availability (RA) of 0.6). From a P budgeting standpoint, this means manure is 60% as effective at increasing soil test P as the same amount of total P applied as fertilizer.