SOIL CONTAMINATION OF PLANT-SURFACES FROM GRAZING AND RAINFALL INTERACTIONS

Contaminants often attach to soil particles, and their subsequent envi ronmental transport is largely determined by processes that govern soi l movement. We examined the influence of grazing intensify an soil con tamination of pastures. I;our different grazing densities of sheep wer e tested against an ungrazed control plot. Scandium concentrations wer e determined by neutron activation analysis and was used as a tracer o f soil adhesion on vegetation. Soil loadings (g soil kg(-1) dry plant) increased 60% when grazing intensity was increased by a factor of fou r (p = 0.003), Rain and wind removed soil from vegetation in the ungra zed control plots, but when grazing sheep were present, an increase in rain from 0.3 to 9.7 mm caused a 130% increase in soil contamination. Multiple regression was used to develop an equation that predicts soi l loadings as a function of grazing density, rainfall and wind speed ( p = 0.0001, r(2) = 0.78). The model predicts that if grazing managemen t were to be used as a tool to reduce contaminant intake from inadvert ent consumption of resuspended soil by grazing animals, grazing densit ies would have to be reduced 2.5 times to reduce soil loadings by 50%.