Physical and thermal characteristics of dairy cattle manure

Greenhouse and regulated gas emissions from animal waste are naturally mediated by moisture content and temperature. As with soils, emissions from manure could be readily estimated given the physical, hydraulic, and thermal properties are described by models and microbes and nutrients are not limiting factors. The objectives of this study were to measure and model physical, hydraulic, and thermal properties of dairy manure to support advanced modeling of gas and water fluxes in addition to solute, colloid, and heat transport. A series of soil science measurement techniques were applied to determine a set of fundamental properties of as-excreted dairy cattle manure. Relationships between manure dielectric permittivity and volumetric water content (θ) were obtained using time-domain reflectometry and capacitance-based dielectric measurements. The measured water retention characteristic for cattle manure was similar to organic peat soil. The unsaturated hydraulic conductivity function of dairy manure was inferred from inverse numerical fitting of laboratory manure evaporation results. The thermal properties of dairy manure, including thermal conductivity, thermal diffusivity, and bulk volumetric heat capacity, were also determined using three penta-needle heat pulse probes. The accuracy of the heat capacity measurements was determined from a comparison of theoretical θ, estimated from the measured thermal properties with that determined by the capacitance-based dielectric measurement. These data represent a novel and unique contribution for advancing prediction and modeling capabilities of gas emissions from cattle manure, although the uncertainties associated with the complexities of shrinkage, surface crust formation, and cracking must also be considered.