ABSTRACT
Phosphorus (P) is a primary nutrient necessary for plant growth. When the P level in soil is below what is essential for plant needs, P is supplied to the soil by the addition of P fertilizer or organic residuals (i.e., manure). Because of the P fertilizer use in the past few decades or application of manure or other organic residuals, a greater portion of the soils in each state in the United States have soil test P levels that exceed the critical level for plant growth. The excess P in soil is then subjected to leaching loss or transport in surface runoff either in soluble or in particulate (sediment-bound) forms. Phosphorus that is moving downward in the soil profile can eventually reach the ground water, especially in areas with shallow or perched groundwater. Phosphorus moving downward in the soil may also be intercepted by artificial drainage systems (i.e., tile drains) that are located within 1-2m from the soil surface.
