Reaction of three veld grasses to different schedules of grazing and resting. 1. Patterns of shoot growth

Abstract

Seven defoliation treatments involving grazing at three-weekly intervals with sheep until mid-January or mid- March, or for the whole growing season, at each of two stocking rates, or resting for the whole growing season, were applied on veld during the 1985-86 season. Mass per unit basal area of the shoot components, green leaf, dry leaf and stem plus inflorescence of populations of tufts of the three most abundant grass species, Heteropogon contortus, Themeda triandra and Trachypogon spicatus, was determined at intervals during the periods of rest. Relative utilization was estimated by observations on samples of tufts after each grazing occasion. Within treatments, growth patterns during rest periods of the populations of the three species were broadly similar, though production per unit tuft basal area decreased in the ratio 100:65:40 for Trachypogon, Themeda and Heteropogon respectively. Using the cumulative growth curves, absolute and relative growth rates for the whole shoot and green leaf in certain of the treatments were established. A pervasive feature of the growth patterns was a tendency towards senescence in the latter half of the growing season. Defoliation by grazing was only partially effective in delaying this process. Amounts of herbage of each species which were present at the start of the rest periods beginning in mid-January and mid-March were generally proportional to the stocking pressure prior to the rest. However, within species, there was a poor correlation between this result and estimated relative utilization. © 1989 Taylor & Francis Group, LLC.