Rheology and Flowability Properties of Liquid Dairy and Swine Waste

Preferential flow of liquid animal manures to tile lines has led to some Midwestern farmers and commercial manure applicators polluting water bodies of a state. These flows have resulted because of large macropores (up to 12 mm diameter or 0.47 inches) in the soil. However, this occurrence is not predictable based on the current understanding of liquid manure properties and soil properties, but is most likely associated with solids content, size and shape of particles in the manure, and macropore (worm holes, cracks, root channels) size and length. This paper reports how moisture content and viscosity of dairy and swine liquid manures affects its ability to flow based on laboratory studies on flow rates of manure through macropores of 7.24 mm (0.285 inches) and 1.27 cm (0.5 inches). Results showed viscosity decreased exponentially as moisture content increased and that dairy manure had a higher viscosity than the hog manure at comparable moisture level. Results of a 29 hole 7.24 mm sieve test showed swine manure with solids 13.2% and dairy manure with 5.8% had flow-abilities 1/10 that of water. Results of a 0.5 inch funnel test indicated hog and dairy manure would not flow if greater than 20% and 13% solids, respectively, even if the soil had holes as large as 0.5 inches. Results of this work show that lowering manure moisture , i.e. increasing solids, would be effective in preventing preferential flow at time of application.