Particle Size and Nutrient Distribution in Fresh Dairy Manure

Particle size was quantified in dairy manure from three different age groups; lactating cows, heifers, and calves. Manure was separated according to five different screen sizes: 2.0, 1.0, 0.5, 0.25, and 0.125 mm. The material on each screen was analyzed for Total Solids (TS), Nitrogen (N), Phosphorus (P), and Potassium (K). The majority of nutrients in the manure were found to be associated with particle sizes smaller than 0.125 mm, specifically 86% of N, 85% of P, and 99.8% of K. Furthermore, particle sizes smaller than 0.125 mm accounted for 46% of TS. Maximum expected removals with standard mechanical separators used on dairy farms would be 19% TS and 5% of N, 5% of P, and 0.07% of K excreted as fresh manure when 2.0-mm screen is used. Maximum anticipated removal when a double screen separator system is used is 31% of TS, 7% of N, 7% of P, and 0.09% of K excreted as fresh manure with both the 2.0- and 1.0- mm screens. Actual removal values under field conditions would vary depending on particle size and quantity of bedding used.