Assessing Certified Manure Analysis Laboratory Accuracy and Variability

Abstract

HighlightsManure analysis proficiency laboratories were assessed for accuracy and precision.Total nitrogen analysis was accurate and precise and is a strength of industry.Ammonium analysis resulted in most variability in laboratory results.Phosphorus and potassium mean comparison indicated significant differences between lab results.Abstract.Nutrient management planning (NMP) is an effective method for ensuring proper nutrient applications to agricultural fields. At livestock facilities, quantifying manure nutrient content is crucial for producers to obtain accurate and precise data to properly apply nutrients to the field to optimize crop yields while minimizing nutrient losses to the environment. In this study, eight manure analysis proficiency program (MAP) certified laboratories each received six replicates of four manure samples (two dairy and two swine) and analyzed for total solids (TS), total nitrogen (TN), ammoniacal nitrogen (NH4-N), phosphate (P2O5), and potash (K2O). Laboratories were compared using the MAP robust statistics comparison approach and a one-way ANOVA using laboratory means. Total nitrogen analysis had high precision and accuracy across laboratories selected for analysis. However, laboratories had less accuracy and precision in determining NH4-N concentrations. Additionally, while P2O5 and K2O met MAP standards for accuracy and precision, there was concerns for reading accuracy, as the median absolute deviation (MAD) to overall median ratio was high (ranging from 5.9% to 14.4%) and many of the laboratory means were statistically different. Keywords: Laboratory variability, Manure, Nutrient analysis.