Sorgo sacarino: interações entre déficit hídrico e época de colheita na produção de biomassa, qualidade de caldo e vigor de sementes

Abstract

The objective of this work was to evaluate the effect of the interval between irrigations during the reproductive stage and the harvest season on: a) the production and partition of fresh biomass and sorghum from sweet sorghum plants; b) the technological parameters of the culture aiming at ethanol production and leaf concentration of macronutrients; c) and the physiological maturation and vigor of seeds produced under such conditions. For this, or this, two experiments were conducted in a greenhouse, in Federal Institute of Education, Science and Technology of Ceará campus Umirim and campus Limoeiro do Norte, with the cultivar of sweet sorghum BRS 511. The factors consisted of three irrigation managements during the reproductive phase (full irrigation; irrigation every 4 days and 8 days) and the harvest was carried out at four different seasons (86, 94, 102 and 110 days after sowing - DAS) aiming to evaluate the biomass production and two seasons (102 and 110 DAS) to evaluate seed maturation. The replacement of water every 8 days caused a sharp reduction in the leaf area, with a reduction of 36.3% in the 1st experiment and up to 100% in the 2nd experiment. The production of total fresh matter showed high average values under continuous irrigation (1st experiment = 223.8 g plant-1 and 2nd experiment = 277.6 g plant-1). Most of the variables showed a reduction in their values with the late completion of the harvest, except for the partition of fresh and dry stem material in the 1st experiment, which obtained an increase of 10.3 and 37.13%, respectively. The harvest at 102 after sowing showed a higher volume (82.52 ml plant-1) and broth extraction efficiency (40.26%). The application of irrigation every 8 days caused a reduction of up to 26.4 and 29.2% in the nitrogen and phosphorus leaf content, respectively. The production of seeds per panicle and the weight of a thousand seeds was significantly influenced by the increase in the interval between irrigations in the 2nd experiment, with a reduction of 50.4 and 46.3%, respectively. There was also a reduction of up to 43.4% in the first germination count and 16.3% in the germination. Thus, the replacement of water every 4 or 8 days associated with late harvest does not favor a good production of biomass and soluble solids, impairing the estimated ethanol yield. In order to produce high quality seeds, the culture of sweet sorghum must be irrigated daily during the reproductive stage.