PO 46: Describe environmental effects from nutrient loss by:

Erosion is the loss of soil particles, often due to wind or water.  Ammonium N (NH₄⁺) is a cation, and thus is readily adsorbed onto the soil CEC.  This holds the ammonium N in a readily-available form which is not susceptible to leaching or denitrification.  However, since most of the CEC is in the clay fraction of the soil, and since this is the fraction that is most susceptible to detachment and erosion, there can be a significant loss of available N when erosion occurs.  Similarly, P is held mainly in insoluble forms in the soil, thus making erosion the predominant mechanism for P loss.  When the eroded soil enters water, the dilution effect will solubize some of the P, which can lead to eutrophication.

Runoff represents a loss of nutrients dissolved in water that drains off a field.  P is commonly lost through runoff.  The capacity for a soil to fix P is very large; however, it is not infinite.  It is possible to add enough P to use up most of the available Fe and Al (which bind it to soil particles), at least in the surface soil.  When this happens, the soil is said to be saturated with P.  Thus, additional P is not fixed, and it remains soluble and can be lost with runoff.  This becomes very important when large amounts of P are added to the soil surface.  The surface layer of soil can become saturated very quickly, and then when there is runoff over the surface, it interacts with this saturated surface soil layer and picks up significant amounts of soluble P and transports it off the field.  If this runoff goes into a water body, the P is immediately available to cause eutrophication.  In very sandy soils with little natural Fe and Al, there is little capacity to hold the P, and thus it becomes saturated more quickly.  In these soils, soluble P loss is an even greater concern, and even P leaching can be significant.