Forage dry mass accumulation and structural characteristics of Piatã grass in silvopastoral systems in the Brazilian savannah

The presence of trees in silvopastoral systems causes changes in the microclimate of the understory where there is the cultivation of forages. This study evaluated the forage dry mass and the structural characteristics of Piatã grass under two densities of trees in a silvopastoral system, in contrast to a treeless area in the rainy and dry seasons of the Brazilian savannah region, so called Brazilian Cerrado. The forage was Brachiaria brizantha cv. BRS Piatã and the tree species was the eucalyptus (Eucalyptus grandis × E. urophylla) planted in the North-South direction in the treatments: forage grown in treeless area (control); forage grown in eucalyptus understory with spacing between rows of 22 m (SSP22); forage grown in eucalyptus understory with spacing between rows of 12 m (SSP12). The experimental design was a randomized complete block with three replications and evaluations conducted from April 2013 to April 2014. There was a reduction in cumulative dry mass and in accumulation rate of Piatã grass in silvopastoral system in the rainy season and the Western side suffered greater interference from trees during this season. For every 1% reduction in photosynthetically active radiation occurred a decrease of 1.35% in the forage dry mass, corresponding to 42.8 kg ha−1. The structural characteristics of Piatã grass have changed in both dry and rainy seasons in silvopastoral system. The spacing between rows of Eucalyptus greater than 22 m is less damaging for pasture productivity when the trees of the silvopastoral system are planted in North-South direction.