How does P behave in the soil?

In most soils, the P content of surface horizons is greater than that of the subsoil. Phosphorus is cycled from roots to aboveground parts of the plant and is redeposited in crop residues on the soil surface. This builds up organic material and stimulates biological activity in surface layers.

In reduced tillage systems, fertilizers and manures are applied to the soil surface with little or no mechanical incorporation, thus exacerbating P buildup in the top 2 to 5 inches of soil.