Chemical composition of two warm-season perennial grasses subjected to proportions of defoliation

摘要

Two experiments were conducted to assess the effect of pre-grazing heights and proportions of defoliation on morphological and chemical composition of the grazing layer of two warm-season perennial grasses of contrasting structures (tall tufted grass-elephant grass, Exp. I; small size stoloniferous grass-kikuyu grass, Exp. II) under intermittent stocking management. The treatments were as follows: Exp. I-factorial arrangement between two pre-grazing heights (90 and 120 cm) and two proportions of defoliation (removal of 50% or 70% of the initial pre-grazing heights); Exp. II-four pre-grazing heights (10, 15, 20 and 25 cm) combined with the same proportion of defoliation (50% of the initial pre-grazing heights). Forage samples were collected at pre-grazing heights and clipped into the grazing layer (cutting heights defined by treatments). The following variables were analyzed: (a) forage mass; (b) proportion of leaves, stems, and dead material; (c) crude protein, neutral detergent fiber, and acid detergent fiber contents. In a general way, there were no significant differences in morphological and chemical composition of the grazing layer of treatments with proportions of defoliation of 50%. Although the treatments of 70% (Exp. I) and 10 cm (Exp. II) showed some differences, both targets impaired the grazing process and were considered as unpractical under field situations. It was concluded that forage chemical composition of warm-season perennial grasses does not change in the upper half of the sward within a range of pre-grazing heights, provided moderate proportions of defoliation (around 50%) are used.