Sweet sorghum for ethanol production in the semi-arid: response to potassium silicate and maturation

The sweet sorghum is an important alternative source to ethanol production, and in a function of its rusticity and tolerance to adverse environment present high potential to Brazilian semi-arid region. With the purpose of seeking recommendations to improvements in agronomic performance, the objective of this study was to assess the biomass yield and juice quality of sweet sorghum cultivars as a function of foliar fertilization with potassium silicate and determine the optimal harvest time. The experiment was conducted in the semi-arid region (Pentecoste, CE, Brazil) in 2014 and 2015, using three genotypes (BRS 506, BRS 511 and EJX 7C30) fertilized with potassium silicate (0, 500, 1000 and 1500 mL ha(-1)) and harvested at 90, 97, 104 and 111 days after sowing (DAS). The experiment was arranged in randomized blocks with four replications in a split-split-plot design (3 x 4 x 4). The total biomass and juice yield, total soluble solids (degrees Brix), total soluble carbohydrates and estimated ethanol production were determined for each year. In 2014, the mean biomass yield for BRS 506, BRS 511 and EJX 7C30 were 58.6, 64.9 and 24.5 Mg ha(-1), respectively. As for 2015, the biomass yield of BRS 506 and BRS 511 decreased by 8.5 and 21 %. The juice of BRS 506 and BRS 511 showed a high quality standard, and the latter cultivar stood out with 157 g L-1 of total soluble carbohydrates at 111 DAS. The cultivars BRS 506 and BRS 511 showed high juice quality when harvested at 111 DAS.