Runoff and sediment yield from snowmelt and rainfall as influenced by forage type and grazing intensity

Currently, there is interest in Western Canada in extending the grazing sea son using perennial and annual forages. Of greatest concern is the environm ental sustainability of these grazing systems, with emphasis on their abili ty to withstand erosion. A study to examine the runoff and sediment yields of annual and perennial forages in central Alberta was initiated in 1994. R unoff and sediment yield were quantified under snowmelt and rainfall events for two seasons. Rainfall simulation was used to further examine runoff un der growing season conditions. Four forage treatments (two annuals: tritica le and a barley/triticale mixture and two perennials: smooth bromegrass and meadow bromegrass) and three grazing intensities (light, medium and heavy) were studied, each replicated four times. Total annual runoff was dominate d by snowmelt. Generally runoff volumes, sediment yields, sediment ratios a nd runoff coefficients were all low. Bare ground increased with increasing grazing intensity and was significantly greater in annuals than perennials for all grazing intensities. Litter biomass decreased with increasing grazi ng intensity and was generally similar in all species for both years at hea vy and medium grazing intensities. Results from the rainfall simulation cor roborated those under natural rainfall conditions and generally indicated t he sustainability of these grazing systems at this site.