Rock phosphate, bone meal, and superphosphate are suitable. The acids formed during composting will aid in solubilization of rock phosphate, converting some of it to a material that is similar to superphosphate. Many procedures for composting call for adding of lime or wood ashes to the pile. Adding of these materials should be avoided. The increase in alkalinity from their addition will accelerate the loss of ammonia by volatilization and will lower the value of the final compost.
Compost piles undergo changes in pH as composting proceeds.
The initial reaction of the pile will be acidic, but development of this acidity is part of a natural process. These organisms die out as the composition of the residues changes. Another group of microorganisms then dominates in the process of composting. These organisms use different substrates and have different effects on pH than the original group. Nothing needs to be done to alter this sequence of events.