Reaction of three veld grasses to different schedules of grazing and resting. 2. Residual effects on vigour

Abstract

Seven defoliation treatments involving grazing at intervals with sheep until mid-January or mid-March, or for the whole growing season at each of two stocking intensities, or resting for the whole growing season (control treatment) were applied on veld during the 1985-86 growing season. Residual effects of the treatments on root mass and the mass of non-structural carbohydrates (NSC) in the roots of populations of the three most abundant grass species, Heteropogon contortus, Themeda triandra and Trachypogon spicatus were determined in the winter of 1986. Shoot yields in the 1986-87 growing season were measured by harvesting species separately on both a tuft basal area and quadrat basis. In general, the defoliation treatments resulted in marked reductions in root and NSC mass in all species as compared with the control. Residual effects on shoot yields were relatively small, and, in sharp contrast to previous findings, correlations between effects on roots and on shoot yields were, except in the case of Trachypogon, generally poor. Discrepancies were found between the residual effects on shoot yields of species measured on a per unit tuft basal area or a quadrat basis. The implications of such discrepancies are discussed. © 1989 Taylor & Francis Group, LLC.