Shavano SCD - Best Management Practices page 23

5.0 - BMPs for Phosphorus Fertilizer Management
Introduction Phosphorus (P) is an essential nutrient for plant growth. Phosphorus in most Colorado soils is tightly held to soil particles and does not leach; therefore, P from agricultural sources generally does not pose a threat to the Uncompahgre Valley water resources. However, the P held in organic phases from residues such as manure can dissolve in water and be lost if improperly managed. Absorbed P on soil particles can cause surface water contamination as P containing sediments move off the land in agricultural runoff. When large amounts of nutrients enter lakes and streams, they enhance the growth of algae and other aquatic weeds, thus killing more desirable species. When added to soil, P fertilizer undergoes several different reactions, including adsorption on soil particles and precipitation. A number of factors determine the speed and fate of the reactions. They include soil pH, moisture, and texture; chemical properties of the soil; and the form of fertilizer used. The net result in most Colorado soils is fixation of P by calcium in relatively insoluble and unavailable forms.	For this reason, recommendations for soils low in available Poften exceed actual crop removal. Producers can obtain maximum P benefits, while minimizing adverse environmental impacts, by adopting the appropriate components of the following BMPs. *Guidance Principle* Manage phosphorus application to maximize crop growth and economic return while protecting water quality. BMPs for Phosphorus Fertilization 5.1 Soil testing is the first step in a sound P management program and should be done a minimum of once during each crop rotation cycle. It is important to account for the P available from the soil and from outside sources such as manures and sewage sludge biosolids. Surface soil samples should normally be taken from the top six to eight inches of the soil or to the depth of the tillage layer.
Phosphorus deficiency in corn	5.2 Broadcast applications of P should be incorporated into the soil (except on perennial forages) following application. Band applications of P should be done on as many crops as feasible because it places the P where it is readily available to the plant, reduces input costs, and minimizes chances of surface runoff. 5.3 Manure is an excellent source of P for crop production; however, manure applications need to be incorporated when applied to soil to prevent potential runoff of both soluble and sediment-associated nutrients to surface waters. *5.4* Conservation practices to minimize soil erosion will also minimize potential losses of P to off-target sites (i.e., buffer strips, filter strips, conservation tillage, residue management).
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