Manure increases the solubility of P in soils, whether applied once or repeatedly. Long-term application of manure often results in the build-up of soil P to the point that a critical degree of soil P saturation is reached. Although this is good in terms of crop yield potential, the risk of P transfer from soil to water bodies may increase. Areas characterized by a high density of confined livestock operations are more at risk than others. Several modes of transport can result in P transfer from soils to waters. Results from studies conducted in the Prairies indicate that the calcareous nature of the soils does not preclude the downward movement of P deep into the soil profile. Movement of P will probably be accentuated by irrigation or incidental flooding. Overland transport by wind and water probably dominates in the Prairies, but subsurface transfer by lateral flow or seepage may also contribute to the load of P reaching water bodies. Areas most at risk can be identified by the Phosphorus Index (PI).
However, the PIa