Source: Dou, Z., D.T. Galligan, R.D. Allshouse, J.D. Toth, C.F. Ramberg, Jr., and J.D. Ferguson. 2001. Manure sampling for nutrient analysis, variability and sampling efficacy. J. Environ. Qual. 30:1432-1437.

Managing manure nutrients is essential for good crop production and environmental care. To reduce environmental impact, it is necessary to obtain trustworthy estimates of nutrient concentrations in the manure. If manure nutrients are not sufficient, this may result in a decrease of crop yield, and if there is excess, this may contribute to pollution of water resources. It is necessary then to control the amount of manure nutrients applied so that they meet but do not exceed crop requirements. Published book values are available that provide average nutrient concentrations, yet on-farm manure sampling and nutrient testing is highly desirable because site-specific conditions cause concentrations to be highly variable. For example, total N concentration can vary by 32.2% for 5 samples to 75.9% for 15 samples in a farm that does not use agitation. This clearly illustrates the possibilities of variability and unreliable results. Manure management that includes agitation of stored manure can substantially reduce variability within manure handling systems. To determine nutrient contents, three to five samples should be used for the agitated systems, and 40 or more samples for the non-agitated. Sample variability within farms is expressed as the coefficient of variation (CV). For farms that used agitation of manure storage's, CV was mostly 6 to 8%, but on farms where no agitation was applied, CV was much higher, 20 to 30%. The authors conclude that standard book values are inadequate for guiding manure application practices. In order for sampling and testing to be accurate and reliable, multiple samples should be used and agitation should be practiced. The underlying message is that manure sampling for nutrient analysis should be advocated similarly to soil nutrient testing to encourage environmentally responsible management of manure.

Abstract author: Sonia Gil Montero, 29 October 2001.

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