Biomass components and structural features in Guinea grass under different frequencies and intensities of defoliation

Abstract

The objective of this work was to evaluate the effect of frequencies and intensities of defoliation on the biomass components and on the canopy structure of Guinea grass (Panicum maximum 'Aruana IZ‑5') pasture under intermittent sheep stocking. Two defoliation frequencies (DF), with 85 and 95% interception levels of the photosynthetically active radiation (Ipar) incident on the top of the canopy, and two defoliation intensities (DI), with residual leaf area index (LAIr) of 1.0 and 1.8 were evaluated. A completely randomized design was carried out, in a 2x2 factorial arrangement. Biomass components and the structural features in the pre‑grazing conditions were affected mainly by DF, with the reduction of green biomass of culms and of dead forage, and were also affected by the increase in the height of the first alive ligule. Pastures managed with lower DF provided lower leaf blade/culm ratio, with 1.65 average, while pastures managed with greater DF showed 2.40 mean leaf blade/culm ratio. Components of the residual biomass were affected by the DI, with a greater residual green forage biomass in pastures managed with LAIr of 1.8. Swards grazed at 95% Ipar and 1.8 LAIr showed residual green biomass of culms and residual dead forage biomass superior to those of the other managements. For grazing by sheep, 'Aruana' Guinea grass should be managed with a 85% Ipar frequency and defoliation intensity corresponding to LAIr of 1.0.