A Procedure for Predicting Soil & Phosphorus Loss with Cover Crops Using the Wind Erosion Prediction System (WEPS) Model. J.J. Grigar, USDA NRCS E. Lansing, MI, M. S. Sporcic & J. L. Lemunyon, USDA NRCS Ft. Worth, TX & T. M. Zobeck USDA ARS Lubbock, Tx.

In Michigan, wind erosion events transport soil by saltation and surface creep from level glacial lake bed soils to connecting water bodies.  In the Saginaw Bay Watershed farming is possible because of deep, open surface drains (county drains), subsurface drainage, and roadside ditches.  Soils are predominately loam, sandy loam and loamy sand texture and occasional beach ridges which are susceptible to wind erosion.  According to the 2003 USDA-NRCS Nation Resource Inventory (NRI), the average annual wind erosion rate from cropland in the United States was 1.7 billion Mg/yr (about 777 million tons).  In Michigan, the average annual rate was 2.20 tons/yr in the 2003 NRI survey.  However, most of the fence rows are gone, leaving wide, unsheltered, level and bare (fall moldboard plowed) fields.  Many fields have unsheltered distances greater than 800 meters (2640 ft.). County drains and berms, the predominant stable border, catch most of the saltation and surface creep eroding from wind erosion.  This windblown sediment is deposited directly into the drains.  The USDA Wind Erosion Prediction System Model (WEPS) can predict wind erosion rates and field boundary sediment loss by partitioning wind erosion into saltation, surface creep, suspension and PM 10.  For this study a procedure was developed with WEPS using a phosphorus enrichment factor to estimate phosphorus loss by wind erosion transported with sediment to open drains.  Using historical soil test P levels for the Saginaw Bay Watershed with an enrichment factor indicated average P loss of 6.2 pounds per acre under the conditions of little or no conservation.  However, cover crops in the crop rotation can reduce phosphorus loss to drains up to 90%.  Additional wind erosion research and soil testing is needed to validate the P enrichment factor procedure to predict the effect conservation practices such as cover crops have on environmental planning and water quality assessment.