Abstract
Some recent papers have recommended moderate intensities of defoliation in order to maximize herbage intake at different time-scales. Most of them, however, did not assess the grazing dynamics of individual tillers during the stocking period. Therefore, the objective of this work was to describe the defoliation dynamics of kikuyugrass (Pennisetum clandestinum Hochst ex. Chiov) pastures subjected to different intensities of defoliation (40, 50, 60, and 70% of the initial height). Twelve 1500 m2 plots were strip-grazed over 24 h, and the frequency and severity of defoliation of individual tillers were assessed in 40 tagged tillers per experimental unit. From these data (n = 1920), we calculated the grazed area in the upper, second, and third horizon, and the total grazed area. We found that the frequency of defoliation by leaf category (expanding, mature, and senescent) increased linearly with the intensity of defoliation, and that reductions in extended tillers could not be used as a proxy to estimate the frequency of defoliation. Moreover, 22% of the second and third horizons were already exploited with intensities of defoliation of 40%, raising the possibility that the exploitation of lower grazing horizons could be more related to stocking density and relatively independent of the grazed area.
Highlights
Defoliation dynamics in pastures can be characterized by both the frequency and severity of defoliation of individual tillers [1]
The frequency of defoliation is closely related to the average stocking density used within a period of time [2]; from this perspective, Wade [3] demonstrated that the frequency of defoliation is linearly related to the stocking density
The severity of defoliation is influenced by factors related to the canopy structure, such as height, bulk density, and the physical barrier imposed by the presence of stems [4,5,6]
Summary
Defoliation dynamics in pastures can be characterized by both the frequency and severity of defoliation of individual tillers [1]. The severity of defoliation (proportion of material removed at each bite event) is influenced by factors related to the canopy structure, such as height, bulk density, and the physical barrier imposed by the presence of stems [4,5,6]. Is relevant for understanding the grazing dynamics, mainly in pastures under intermittent stocking. According to these authors, animals seek to harvest the first horizon (upper half, composed mostly of leaves) until approximately 70–75% of this horizon has been removed; in terms of the intensity of defoliation (proportion of canopy height removal), this would correspond to a reduction of approximately 40% of the pre-grazing height [10]. As herbage depletion increases beyond these levels, animals would progressively graze lower horizons composed of higher proportions of high tensile
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