Similar to nitrogen fertilization, a variety of chemical and environmental factors influence the potential for off-site movement of phosphorus. The primary means of off-site movement is by runoff due to phosphorus content at or near the soil surface. Improper handling of organic waste, notably clippings, can also be a significant source of phosphorus movement off-site, and thus clippings should not be placed in or near storm water treatment structures or wetlands. Finally, phosphorus leaching can occur, but only under very specific soil and chemical situations.
Phosphorus Runoff
Turfgrass, like other untilled systems, accumulates higher concentrations of soil P in the upper soil profile (0 to 2 inches) compared to lower depths. Frequent P fertilization, especially at higher rates, substantially increases the soil P levels in this upper profile. Consequently, P in fertilizer can be lost in runoff, as much as 20% of P fertilizer. Runoff can also wash away soil sediment and plant debris with mineral P and organic P. The runoff risks are very high during turfgrass establishment due to limited plant utilization and more runoff present than in established turf.
Phosphorus Leaching
In its rare anionic form, phosphorus can leach and is a concern for water quality issues. P leaching potential is best managed by applying P based on soil test results. When phosphorus is complexed with other elements in the soil, however, it has a low leaching potential unless it has been over applied for many seasons. Sandy soils, on the other hand, often have a low potential to fix (tie up) P and therefore are more likely to have a P leaching problem.
