Nutrient variability in manures: Implications for sampling and regional database creation

ABSTRACT:

The variability of manure nutrient levels within and across farms makes manure sampling and development of reliable tabular values challenging. The chemical characteristics of beef, dairy, horse, sheep, and chicken solid manures in Colorado were evaluated by sampling six to ten different livestock operations for each manure type and comparing the results to values found in the literature. Due to the semi-arid climate of Colorado, manure tends to be drier and have lower ammonium (NH₄-N) levels and higher phosphate (P₂O₅) and potash (K₂O) levels than those reported in the Midwest. Within-farm variability was assessed by analyzing ten sub-samples from each of nine manure sources. Coefficients of variation were calculated and the sample numbers necessary to achieve 10% probable error were determined. On average, about 25 sub-samples are necessary for nitrogen (N), phosphorus (P), and potassium (K) characterization of solid manures, but determining NH₄-N and nitrate (NO₃-N) concentrations requires over 100 sub-samples to form a representative sample, due to their relatively low concentrations. Data from Colorado, Utah, and New Mexico were combined to form a Mountain West Manure Database. The manure types, with a minimum of 72 farms represented in the database, have narrow confidence intervals. Until we have adequate sample numbers (>72 farms) to establish reliable table values based on local data for all manure types, manure sampling will be recommended.