Vigor of needleandthread and blue grama after short duration grazing

Abstract

Grazing treatments were applied to pastures in western Nebraska from 1980 through 1983 to examine the influence of short duration grazing (SDG) on plant vigor. The 3 treatments were: (1) 4 years of SDG, (2) 3 years of SDG followed by 1 year of rest, and (3) 4 years of rest. Total nonstructural carbohydrate (TNC) concentrations of stem bases, mean tiller weight, and tiller number/plant of etiolated growth, and paired differences in spring growth between covered and uncovered plants were used to evaluate vigor of needleandthread (Stipa comata Trin. & Rupr.) and blue grama [Bouteloua gracilis (HBK) Lag. ex Griffiths]. Two 7-pasture, 1-herd SDG systems were used. Length of use and deferment periods, stocking density, stocking rate, and sequence of pasture use were constant throughout the study. Grazing treatments reduced the vigor of both study species, but the vigor of blue grama was more sensitive to treatments than needleandthread. Levels of TNC in needleandthread were not affected by grazing treatments. Concentrations of TNC in blue grama recovered to levels of ungrazed plants after 1 year of rest in some but not all pastures. Grazing increased the number of tillers/plant, but reduced total organic reserves of both species as measured by etiolated growth. Assimilates produced in early spring growth appeared to be more important for tiller initiation in plants that had been grazed than in ungrazed plants.