Desenvolvimento de fertilizante organomineral fosfatado a base de borra de café tratado termicamente para fins de liberação lenta

Abstract

Brazil is one of the largest agricultural producers in the world, with a growing demand for planted areas. However, Brazilian soils need supplementation of various nutrients, including phosphorus (P), besides sources of organic matter. Since traditional fertilization has low efficiency due to losses such as leaching and volatilization and P fixation in the soil, the use of slow-release fertilizers can optimize fertilization performance. Nevertheless, such fertilizers are expensive, making their use unfeasible. In this context, the use of organo-mineral fertilizers based on biomass can be a sustainable alternative for soil nutrition and increased agricultural productivity. Because of this, the objective of this work was to produce pelletized organomineral fertilizers of slow-release, from coffee grounds (CG) impregnated with a triple superphosphate paste (TSP). A 2³ factorial experimental planning was implemented in order to evaluate the influence of the percentage of binder (sugar cane molasses), of the mass ratio between TSP and CG and the drying temperature, on the pellet resistance and its release capacity nutrients in the water. The release kinetics of P was studied using the Weibull and Korsmeyer-Peppas kinetic models. The fertilizer with the best performance was submitted to thermal treatment (TT) in a muffle, at temperatures of 300 and 400 ºC by different exposure times (10, 30 and 90 minutes). Then, the mass loss kinetics during TT was evaluated using a global reaction model; the fall resistance of the new pellets and the release kinetics of P. The characterization of CG revealed its great potential as a soil conditioner. The study of fertilizer formulation showed that the addition of molasses and the amount of fertilizer were the factors that influenced the mechanical resistance of the pellet the most. The formulation with 10% molasses and 2.5 g fertilizer / g CG, dried at 100ºC showed the best resistance to falling and a slower release of P, taking about 13.8 h to release 90% of P. As for TT, the loss of mass due to devolatilization followed first-order kinetics. The TT fertilizer at 400ºC for 30 min showed the best performance and it complies with the slow release classification requirements. It showed kinetics of P release according to the Korsmeyer-Peppas (KP) model, being controlled by the Fickian diffusion associated with the rupture of the pellet by swelling/relaxation of the matrix. The half-life of the release of the optimized sample was 3078 times greater than that of TSP powder and 30 times greater than that of the sample without TT. Thus, it is concluded that TT was essential to increase the performance of the fertilizer, since it increases the resistance of the pellet, creating a stronger bond between the nutrient and the carbonized biomass, which hinders the mass transfer and improves the slow release performance. The formulation developed in this work has the potential to minimize P losses in the soil by leaching, to increase water retention in the soil, in addition to providing organic matter, acting as a soil conditioner.