Get reliable rangeland science

Historically over 50 years of rainfall/runoff research using rainfall simulators has been conducted at various rangeland sites in the West, however these sites rarely have consecutive yearly measurements. This limits the understanding of dynamic annual conditions and the interactions of grazing, plant productivity, and annual weed presence on runoff, infiltration and erosion. Rainfall runoff was measured with a rotating boom rainfall simulator on plots defined as light, moderate and heavy grazing. Simulations were conducted for three consecutive years at the Central Plains Experimental Range, Nunn CO. This site has had 53 years of known grazing (Bouteloua gracilis�(H.B.K.),�Buchloe dactyloides�(Nutt.) Engleman). Simulations were also conducted at the High Plains Grasslands Research Station, Cheyenne WY, with 12 years of recorded grazing (Bouteloua gracilis�(H.B.K.),�Pascopyrum smithii�(Rydb.)) The simulator rained on 3 x 10 m plot pairs with controlled rainfall amounts and intensities.� Simulations were conducted when the soil was dry, wet and very wet.� Raining on dry soil allowed evaluation of vegetation, surface roughness, and soil hydrophobicity on water infiltration.� Raining on wet soil measured the effects of soil bulk density and soil organic matter on runoff and infiltration. At the High Plains Grassland Research Station heavy grazing resulted in the greatest runoff, however light grazing showed more runoff than the moderate grazing treatment.� At the Central Plains Experimental Range heavy grazing similarly showed higher runoff rates than lower intensity grazing. Decreasing heavy grazing at the Colorado site resulted in a decrease in runoff within a year of the decrease over the 3 year study period. In conclusion while grazing intensity can effect runoff rates the effect is short term and can be reduced with rotational pasture use.