Nutrient Content for Dairy and Swine Manure in Wisconsin, 1998-2010
John Peters, Department of Soil Science, UW-Madison
The nutrient value of manure can be assigned by using estimated “book” or average available N, P2O5 and K2O content. However, testing manure may better indicate how animal management and other factors actually affect nutrient content. Data in the livestock waste facilities handbook (MWPS, 2007) provides “typical” or average nutrient content for manure of several animal types in the upper Midwest. These values probably give an acceptable estimate for the “typical” producers, especially if sampling methods do not represent the pit, pack or gutter adequately. However, an analysis of a well-sampled system should give a better estimate of the manure nutrient value for individual farms especially if herd and manure management is not “typical”. In Table 1, the MWPS total nutrient estimates are compared to actual manure analysis of samples analyzed by Wisconsin based laboratories between 1998 and June 2010. In most cases the summary values compare quite well with the established norms. The following laboratories; AgSource Laboratory, Dairyland Laboratory, Rock River Laboratory and the UW Soil and Forage Laboratory provided manure analysis results for this summary. The cooperation of these laboratories in providing their data for this summary is greatly appreciated.
Even though on average the actual farm values compare well to the MWPS estimates in most cases, the actual analysis values can range widely from the MWPS estimates as can be seen by the wide ranges found in the data sets. This could be the result of different management practices on farms or other on farm differences, or improper sampling techniques. Taking multiple samples over time and averaging these values will help reduce the potential for using a single anomalous laboratory result as the basis for crediting nutrients on a farm.
Using book values is one way to attempt to properly credit applied nutrients from manure. However, if the manure from any farm varies from the norm, using a standard value may be inappropriate. The alternative is testing and the number of manure samples tested by public and private laboratories has increased greatly from 1998 to their current levels in 2010. Many producers still do not sample manure properly, but by following recommended sampling guidelines and keeping long-term records, the appropriate manure nutrient content values can be obtained for a farm.
MWPS Livestock waste facilities handbook. Handbook #18, 2nd ed. Midwest Plan Service. Ames, Iowa, 2007.