Implicações produtivas de intervenções pontuais de alta severidade em pastos de azevém anual manejados sob lotação intermitente

Abstract

The use and management of pastures, in beef and dairy cattle industry, encounters some impasses regarding the choice of the appropriate management model for each situation. Grazing management has, as one of the main objectives, ensure vigorous regrowth, since the remaining leaf area has a high correlation with the pasture’s potential regrowth. The aim of this study was to evaluate the effect of tactical high level defoliations (70%) on productive and nutritive characteristics of italian ryegrass pastures managed under intermittent stocking method. The experiment was conducted in Pato Branco/PR, Brazil. The experimental treatments consisted of four defoliation strategies, starting from a single pre-cut height of 20 cm: constant severity of defoliation of 40%; severity of 40% with tactical interventions of 70% at the second (70I) or fourth (70F) cut; intercalating (changing) 40% and 70% over the cycles. The treatments were applied following a completely randomized design with three replicates, totaling 12 experimental units. It was evaluated: forage production; morphogenetic and structural characteristics; leaf lamina proportion on upper and lower strata; forage nutritive vale on upper strata (NDF, ADF, CP, in vitro digestibility). The data were grouped as the mean of the experimental unit (i.e. mean of periods), analyzed by GLM of SAS and the means compared by Student’s “t” test. The level of significance was set at 5% (P < 0.05). Regarding canopy structure, only the lower strata had differences among treatments, and the treatment 40 showed the greater levels of forage and leaf lamina mass, and leaf lamina proportion. For morphogenetic and structural characteristics, the treatment 40 showed the greater leaf appearance and elongation rates, LAI, and senescence. The forage production, accumulation rate, and nutritive value, were not different among treatments. Considering the condition applied in this experiment (i.e. pre-cutting height),tactical high level defoliations (70%) seems do not affect forage productive capacity, as well as forage nutritive value, of Italian ryegrass pastures.