Effects of sugar beet pulp on cheatgrass and bluebunch wheatgrass growth under controlled conditions

Abstract

Cheatgrass (Bromus tectorum L.,) an invasive, annual grass species, degrades range and pasture lands by out competing and replacing preferred native grass species resulting in economic and ecological losses. Current control strategies are costly and ecological risky. Soil nitrogen depletion by promoting microbial nitrogen utilization by application of a carbohydrate energy source such as sucrose may decrease cheatgrass's competiveness and permit seedling establishment of preferred native species. Review of the literature reveals attempts at restoration of native grasses and elimination of cheatgrass by nitrogen depletion with sucrose applications have failed or at best achieved limited success. We believe one reason for failure is that soil microbes utilize applied simple carbohydrates such as sucrose too rapidly resulting in only short periods of nitrogen depletion, and that application of sugar beet pulp may promote a longer state of nitrogen depletion. We hypothesize the growth of nitrogen dependent invasive grasses will be inhibited by nitrogen deprivation produced by mulch application of coarse granulated sugar beet pulp, and that the inhibition of growth is not related to a passive mulch effect. In a four armed green house study, we compared cheatgrass and bluebunch wheatgrass growth after application of ground sugar beet pulp at rates of 0.0, 0.5, 1.0 2.0 and 4.0 tons per acre. As a control, granite chicken grit was similarly applied in equal volumes to rule out a passive mulch effect. At 35 days, there was a negative linear relationship between rate of sugar beet pulp application and cheatgrass growth (p <0.001) and BBW growth (p<0.002). The negative effect of sugar beet pulp on cheatgrass growth was twice the negative effect on blue bunch growth. Granite grit application did not decrease growth of either species. We conclude that sugar beet pulp application depresses cheatgrass growth and that the cause is not a passive mulch effect. Our data indicates that longer duration nitrogen deprivation may aid in promoting restoration of cheatgrass dominated acreages, and treatments such as sugar beet pulp application may permit native grass seedling emergence and establishment.