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Manure Phosphorus and Surface Water Protection I: Basic Concepts of Soil and Water P

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Manure P

Livestock in animal feeding operations produce the equivalent of approximately 187 million tons of manure annually in the U.S., based on an average water content of 50 percent. This is approximately equal to a single heap that is 2,640 feet wide at the base and 3,290 feet high, and that may contain about two million tons of phosphate (Fig. 4). Nutrients in this manure are sufficient to meet 25 percent of the nitrogen (N) and P needs, and 45 percent of the potassium need, of the crops produced in the United States.  Efficient manure use can reduce fertilizer need.

Fig. 4.  Agronomically sound use of manure can substantially reduce fertilizer requirements.  (Graphic by Bahman Eghball)



Manure can be challenging to use as a nutrient source because P concentration varies widely with manure type, and manure is a bulky P source. Solid manure may contain only five to 10 pounds P per ton, while concentrations for manures with high water content are even less. Most manure P is in inorganic forms (50 to 95 percent); and, generally, 60 to 70 percent of manure P is estimated to become available to the first crop after application. Manure is bulky and costly to transport to distant fields, often resulting in over-application of manure to fields near the animal feeding operation. Another concern of crop producers is that manure application often results in uneven application of nutrients across a field, due to variation in manure nutrient content and manure physical qualities, and inadequacy of the application equipment or equipment operation. Careful management is required to achieve a uniform application of manure P to the land.

Manure has advantages over chemical fertilizers as a nutrient source. In addition to the nutrients applied, manure application often results in increased yield compared with use of fertilizer alone, possibly due to improved physical, chemical and microbial soil properties. With beef feedlot manure, the liming effect can be significant, and enough to avoid problems of soil acidification.  The equivalent of approximately 60 to 70 pounds of agricultural lime per ton of manure has been measured for typical beef feedlot manure. Following manure application, runoff from heavy rainfall or snow melt events is often less due to improved water infiltration, which often means more water available to the crop and less soil erosion. In a study conducted in eastern Nebraska, runoff from land with composted manure applied was less than half of the runoff where no manure was applied during the years of application. This effect persisted over the four years following the last application of compost as shown in Figure 5.  The online Extension publication, Calculating the Value of Manure for Crop Production, includes a manure value calculator, which can be used to estimate the value of manure, consider nutrients applied and whether these are needed for crop production, the higher yields that may result, as well as the costs of using manure. In short, manure often is an abundant and valuable resource.

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