Water quality in the U.S. is threatened by contamination with nutrients, primarily nitrogen (N) and phosphorus (P). Animal manure can be a valuable resource for farmers, providing nutrients, improving soil structure and increasing vegetative cover to reduce erosion potential. At the same time, application of manure nutrients in excess of crop requirements can result in environmental contamination.
Environmental concerns with P are primarily associated with pollution of surface water (streams, lakes, rivers). Excess P in water causes algae to grow rapidly, or to “bloom.” The decomposition of this algae consumes dissolved oxygen in the water and impairs the survival and productivity of fish, clams, crabs, oysters and other animal life. An algae bloom and subsequent decrease in dissolved oxygen may be caused by runoff of P when application to land is in excess of crop requirements.