Laboratory Evaluation of the Dust-Emission Potential of Cattle Feedlot Surfaces

A laboratory apparatus was developed for measuring the dust-emission potential of cattle feedlot surfaces as affected by manure surface characteristics. A feedlot surface was simulated with a layer of dry, loose, sieved feedlot manure, either with or without a compacted soil layer underneath. The vertical action of the cattle hoof was reproduced by dropping a steel weight onto the manure surface. High-volume samplers for PM sub(10) (paniculate matter smaller than 10 mu m aerodynamic equivalent diameter) were used to collect suspended PM sub(10). The effects of kinetic energy of the falling weight, manure depth, manure moisture content, bulk density, and surface amendment (sawdust, wheat straw, and surface water application) were investigated. For each manure depth, PM sub(10) emission was directly related to the kinetic energy of the falling weight. For each weight drop, PM sub(10) emission did not differ significantly with manure depth. In addition, PM sub(10) emission was inversely related to the manure moisture content. Compaction of the manure surface reduced PM sub(10) emission. Increased amounts of water, sawdust, or wheat straw to the manure surface also significantly decreased PM sub(10) emission in initial tests, but dislodging/displacement of wheat straw and penetration of the wetted surface crust by the falling weight increased the emission potential for subsequent tests. The weight drop test chamber developed is a simple and repeatable method that can be used to compare relative effectiveness of different dust abatement measures. While the measurements are reproducible, the vertical action of the cattle hoof is highly simplified; thus, the WDTC might not fully reproduce the actual vertical action of the cattle hoof on a feedlot surface. In addition, the resulting aerosol may not have similar physical characteristics as those of dust emitted from feedlots.