Avaliação do período de colheita para ensilagem do girassol (Helianthus annuus L.)

Abstract

The production of good quality sunflower silage is influenced by the age of harvest. The objective of this study was to analyze the sunflower silages BRS-323 variety harvested in five different seasons (85, 92,99, 106 and 113 days post-planting), in order to indicate the most appropriate harvesting time. The design was completely randomized with five treatments and five replications, with treatments being the harvesting ages. The plants were mechanically ground into particles of 2.0 to 3.0 cm and ensiled for 35 days in PVC silos, ten centimeters in diameter and forty centimeters long. The dry matter contents varied between cutting ages, with values ranging from 15.41% to 58.67%, and probably influenced the means of losses by effluents, which decreased as dry matter levels increased. The pH values presented a linear increase (P<0.05), with averages varying from 3.62 to 6.45, ammonia nitrogen values were lower than 10%, indicating efficiency in the maintenance of the protein fraction quality. The levels of crude protein and ethereal extract presented positive linear behavior (P <0.05), probably due to the filling of the achenes on the occasion of physiological maturation. The in vitro dry matter digestibility averages varied from 66.60% to 42.42%, being negatively influenced by the value of acid detergent insoluble fiber. The gas loss averages showed a negative quadratic behavior (P <0.05), an inverse behavior to the non-fibrous carbohydrate concentration, suggesting that the reduction of these carbohydrates reduced the substrate for beneficial microorganisms, consequently promoted increase of undesirable fermentations that cause losses of dry matter through production of Co2. Considering the above, it is indicated that the harvest is performed at the stage where the back of the chapter is dark yellow and the bracts still green, a characteristic that is observed at 92 days.