Gramíneas tropicais em condições de sombreamento artificial

Abstract

This research was carried out in the Department of Agricultural Sciences of the State University of Montes Claros (UNIMONTES) in Janaúba-MG, in order to evaluate three tropical grasses (Cenchrus ciliares L., Brachiaria brizantha cv. Marandu e Brachiaria brizantha cv. MG4) in four levels of artificial shading (30, 50, 70 and 80%) and the control. The design was in randomized blocks with four replications, constituting twenty experimental units (plots) of four square meters for every three evaluated species. Two cuts were made to evaluate bufell grass, three cuts to evaluate marandu and MG4 grasses. After collection for laboratory evaluations, plants from all plots were cut to a uniform height of 5 cm above ground level. The collection of material from the plots was performed using sampling parts of 0.25 square meters (50 x 50 cm). Two samples per plot were collected, one to evaluate yield of total dry matter and chemical analyzes, and the other to evaluate morphological and structural characteristics, production of dry matter of stems and leaves, and chemical analyzes of stems and leaves. The buffel grass showed a significant reduction in dry matter production, tiller density and blade:stem ratio in plots with shading. There was a significant increase in the contents of neutral detergent fiber and acid detergent fiber in the buffel grass stem in plots with shading. It was concluded that the buffel grass shows no tolerance to shading. With shading, the marandu grass did not present any significant changes on production of dry matter, tillers density blade:stem ratio, leaf crude protein, total crude protein, leaf neutral detergent fiber and the total acid detergent fiber. It was concluded that the marandu grass presents tolerance to artificial shading up to level of 80%. The MG4 cultivar showed no significant difference for shading treatments on the variables dry matter weight, tiller density, blade length, number of leaves per tiller, stem length, blade: stem ratio, stem neutral detergent fiber, stem fiber acid detergent, leaf and total. The amounts of crude protein of MG4 grass increased significantly in stems, leaves and whole plant in all treatments under shading. A significant reduction in contents of leaf neutral detergent fiber and the total neutral detergent fiber compared to treatment without shading. It was concluded that the MG4 grass is tolerant to shading, and the level of 80% provided the greatest results.