Many soils which have received manure or synthetic applications over a number of years contain relatively high levels of soil phosphorus. In soils which have not been so fertilized, phosphorus levels may be low. Rock powders suc as colloidal phosphate and rock phosphate can be applied to build up the phosphorus-supplying power of a soil over time. However, these products become available to plants very slowly, and cannot be relied upon to supply adequate phosphorus to a crop the year of application when soil level of phosphorus are low. They are more efficiently used by incorporating into a compost-making operation where the.
