Manure Phosphorus

Managing manure resources has become increasingly difficult for producers. Regulations keep everyone guessing what will be happening next. Over the last year, an emphasis of phosphorus management of manure has made nitrogen a secondary concern.

Many types of manure have very high concentrations of phosphorus in relation to what the crop needs and the nitrogen concentration of the manure. Due to environmental concerns of excess phosphorus applications and phosphorus runoff, many states are beginning to regulate manure application. In many areas, these regulations now consider the phosphorus content of the manure first and the nitrogen content of the manure second. Minnesota regulations that were put in place almost a year ago have a phosphorus based regulation in place. Minnesota regulations include the following. There cannot be long- term soil phosphorus buildup near surface waters, and a manure management plan with phosphorus management strategy is required if applying manure to soils with extremely high phosphorus levels and a facility with over 300 animal units. South Dakota and Nebraska are in the process of evaluating the best approach for handling the large amounts of phosphorus in manure. Iowa uses a phosphorus index with three main components to determine the maximum amount of phosphorus to apply. These components are: Erosion Component, Runoff Component, and Subsurface Drainage Component. Each component uses several variables to determine value.

With phosphorus based manure management, the manure will typically have to be applied to more acres and some source of commercial nitrogen will need to be applied to fully meet the nitrogen needs of the crop. The average sample of dairy manure tested at AGVISE Laboratories last year contained 25 lbs./1,000 gallons of Nitrogen and 12lbs./1,000 gallons of phosphate. The average fertilizer recommendation for 160 bushel corn using University of Minnesota recommendations would call for 115 lbs of nitrogen and 30 lbs of phosphate per acre. Sweep injecting 3,000 gallons/acre of this average dairy manure would meet the phosphate requirements of the 160/bushel /acre corn crop. This amount of manure would only supply the crop with 41 lbs/acre of nitrogen, thus an

additional 74 pounds/acre of nitrogen are needed for the crop. This is just one example using average manure and soil analysis. Swine and poultry manures contain higher concentrations of phosphorus, requiring even greater applications of additional nitrogen.

As crop advisors, consultants and fertilizer dealers, it will be important to help producers use their manure and supplement any short comings with commercial fertilizers. As the regulations develop or are changed, it is important for you to be aware of what they are so you can help your growers develop a sound fertility management plan.