Efeitos do manejo nutricional na cultura do sorgo sacarino [Sorghum bicolor (L.) Moench]

Abstract

Sweet sorghum [Sorghum bicolor (L.) Moench], a Poaceae originating in Central-East Africa, has great potential for the production of bioenergy, and is also part of the energy matrix of countries such as China, United States and European Union. In Brazil, due to the importance of sugarcane as a source of renewable energy, research on the agricultural and industrial process of sweet sorghum is still incipient. With regard to fertilization, there are few regions with established recommendations and the nutritional requirements of the available genotypes are practically unknown. The objective of this work was to evaluate whether the increase in doses of primary macronutrients can contribute to the increase in productivity and technological yield of a hybrid cultivar of sweet sorghum. The experiment was carried out in an experimental area at the Federal University of São Carlos (UFSCar), in a randomized block design, with five replications, composed of four doses of NPK fertilization, defined according to the recommendation of the Agronomic Institute of Campinas (Technical Bulletin 200). The recommended doses (RD) were respectively 110-90-120 kg ha-1 of N-P2O5-K2O, constituting the following treatments: 0% of the RD, 50% of the RD, 100% of the RD and 150% of the RD. At 105 days after the emergence of the plants, height (m), stem diameter (mm), number of internodes, stem production (t ha-1), green biomass (t ha-1), dry biomass (t ha-1), dry shoot weight (g plant-1), moisture (%), Brix% juice, pol% juice, fiber (%), total recoverable sugar (kg t-1), and juice purity (%). Increasing doses of primary macronutrients did not provide significant responses (p≤0.05) on the biometric, technological and yield parameters of the sweet sorghum (cultivar NS 105), allowing to conclude that the initial soil fertility was sufficient for the development of the crop. The low industrial quality of sweet sorghum juice was influenced by climatic factors that triggered a high infestation of Ergot, a disease caused by African Claviceps. The maximum productivity and maximum economic productivity dose cannot be determined due to the lack of significant adjustment of the quadratic regression equation.