Vertical biomass distributions for western wheatgrass (Agropyron smifhii Rydb.) from 3 locations in western South Dakota were evaluated to determine effects of location, date, topographic position, past grazing history (vigor), and phenological develop ment. A linear, quadratic regression was used for model develop ment and testing, and analysis was by general linear hypothesis testing. All factors except topographic position were significant; however, only phenological development was useful in a general model for estimating utilization from the percentage of height remaining. This factor was best expressed in 3 leaf-classes of 2-4, 5-6, and 7-10 leaves per tiller. Thus, height-weight relationships can be improved as a biomass predictor if separate regressions are used for these 3 phenological classes.

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