Assessment of Spring Defoliation to Improve Fall Forage Quality of Bluebunch Wheatgrass (Agropyron spicatum)

Abstract

Bluebunch wheatgrass (Agropyron spicatum (Pursh) Scribn. & Smith) was clipped at 4 phenological stages to compare forage quality of subsequent regrowth relative to nondefoliated plants. Following 2 years of treatment, plants clipped at boot, emergence, flowering, and seed formation produced lower levels of ADF and higher values of CP and P than control plants at equivalent phenological stages. Clipping at boot and emergence for 2 years delayed flowering by 16 and 15 days, respectively, while subsequent flowering of plants clipped at flowering and seed formation occurred only sporadically. These delays in plant phenology altered forage quality on 26 October compared to nondefoliated plants. Clipping at boot, emergence, flowering, and seed formation reduced percent foliar ADF, while increasing relative proportions of CP, Ca, and P compared to untreated herbage. Crude protein in plants clipped for 2 years at emergence, flowering, and seed formation averaged 11.9%, 12.5%, and 13.7%, respectively. Phosphorus in regrowth foliage of plants clipped at flowering and seed formation equalled 0.22% and 0.26%, respectively, on 26 October. These values exceed maintenance requirements of cattle and elk, indicating that judicious grazing management can improve nutritive values of bunchgrass vegetation.