INCREASING STOCKING DENSITY REDUCES EMISSIONS OF FUGITIVE DUST FROM CATTLE FEEDYARDS

摘要

The moisture and compaction dynamics of an open-lot corral surface in a cattle feedyard depend strongly on the spatial density at which the animals are stocked. Because the moisture content and bulk density of the corral surface directly influence its intrinsic dust susceptibility, emission of fugitive dust from a feedyard surface should be sensitive to changes in stocking density. In the summer of 2012 we measured airborne dust concentrations upwind and downwind of feedyard pens stocked at two different densities, 718 (control) and 1,435 hd ha(-1), over a 160-d feeding period. Doubled stocking density was achieved in two different ways, by (A) confining cattle to half the pen area using electric-cross fencing and (B) doubling the number of cattle in the pens. Path-averaged dust concentrations were measured upwind and downwind of feedyard pens using an optical particle sizer (OPS model 3330, TSI Inc., Shoreview, Minn) and an earlier-model optical sensor (model DUSTTRAK II 8530, TSI Inc., Shoreview, Minn.) mounted on mobile monitoring platforms. Because the monitoring platforms used different instruments, during the data analysis phase DUSTTRAK data were compared only to DUSTTRAK data, and OPS data were compared only to OPS data. Downwind 1-min concentrations of dust varied from 1 to 4,478 mu g m(-3) for the control pens, 1 to 2,431 mu g m(-3) for the pens with cross-fencing (treatment A), and 1 to 2,872 mu g m(-3) for the pens with twice as many cattle as the control pens (treatment B). Dispersion modeling using AERMOD revealed that the apparent dust-emission fluxes from treatments A and B were 79.4% and 80.6% lower, respectively, than the apparent emission flux from the control pens (23.45 mu g m(-2) s(-1) We conclude that stocking-density manipulation is likely to be a viable Beneficial Management Practice (BMP) for controlling fugitive dust from open-lot cattle feedyards but that improved, path-averaged monitoring techniques appropriate to the feedyard source geometry are needed.