The influence of shading on Massai grass availability in a silvopastoral system

Silvopastoral systems may vary the temperature of air, by providing shade, which contributes to a milder microclimate, resulting in better quality of the pasture. The aim of this study was to evaluate the effect of shading by eucalyptus trees (Eucalyptus urophyllax Eucalyptus grandis) on dry matter yield of Massai grass (Panicum maximum x Panicum infestum) in a silvopastoral system, under rotational grazing, during two summer seasons in Jaboticabal, S?o Paulo State. Treatments were identified as TA = non-shaded Massai grass pasture; TB = pasture of Massai grass with eucalyptus trees spaced 12 x 2 m; TC = pasture of Massai grass with eucalyptus trees spaced 6 x 2 m, and were composed of six paddocks, of 70 m² each, distributed in a completely randomized design. A sward stick and a 0.25m² quadrat were used for measuring pasture height and density, in order to estimate the kg of DM/ha. Light interception (95%) was the criteria for starting grazing period and the residual pasture height was fixed in 20 cm. Pasture mass was assessed by cutting, drying (in a 55^oC air forced oven, for 72 hours) and weighing two representative samples from each paddock of each treatment, determining total forage dry matter yield (DMY). Samples were split in green material (composed of green leaves and green stems) and dead material (all dead material collected in the sward, during cutting process) to assess the green dry matter yield (GY), and dead material dry matter yield (DY). Data were analyzed using GLM procedure of SAS. For both years, the DMY had greater values for TA than TC (year 1:TA: 7372 kg/ha, TC: 5731 kg/ha, P<0.05; year 2:TA: 7534 kg/ha, TC: 4210 kg/ha, P = 0.003;) and did not differ from TB (year 1: 6959 kg/ha, year 2: 5966 kg/ha). The GY had greater values for TA than TC (year 1: TA: 4993 kg/ha, TC: 2872 kg/ha, P<0.05; year 2: TA: 5798 kg/ha, TC: 3215 kg/ha, P = 0.008) and did not differ from TB (year 1: 4449 kg/ha, year 2: 3215 kg/ha). Thus, DY values, from both years, were similar for all treatments. In conclusion, intense shading of Massai grass decreases total and green forage mass yield. However, dead material yield probably does not depend on the amount of shade.