The phosphorus and potassium in manure can be considered equivalent to commercial phosphorus and potassium for building soil fertility. However, as was discussed before, the potential problems must be considered in applying manure directly to legumes. The best time to apply manure phosphorus and potassium to a legume is when the field is in corn. Remember that when manure is applied to corn to meet the nitrogen needs of the corn, excess phosphorus and potassium will be applied. Sulfur and Forages Sulfur deficiency is not a common problem in Pennsylvania.
Acid rain is a major contributor of sulfur in Pennsylvania.
Current soil tests for sulfur are not very reliable. The best approach to diagnosing a sulfur problem is to use plant tissue analysis, taking care to get a proper sample at the appropriate stage of growth. The ratio of nitrogen to sulfur in plant tissue is a good indicator of whether sulfur is adequate or deficient. For example, a nitrogen to sulfur ratio greater than 11 to 1 is an indication of sulfur deficiency in alfalfa. Ammonium sulfate, which is 24 percent sulfur, can be used as the nitrogen source on grasses.