Why is controlling phosphorus important?

Phosphorus is essential to plant growth. Normal applications of phosphorus are relatively harmless. Note however, that when manure application rates are based on nitrogen, the amount of phosphorus applied will often exceed the requirements of the crop. When applied in excess, soluble phosphorus can run off into surface water along with phosphorus attached to soil particles. There, it can greatly stimulate growth of algae and other aquatic plants, resulting in an unhealthy environment for fish and other water life.