Utilização da lignina no desenvolvimento de fertilizante fosfatado de liberação controlada

Abstract

Phosphorus contained in phosphate fertilizers such as MAP (monoammonium phosphate) plays important physiological roles in plants. The challenge is often that phosphorus (P), added to the soil in the form of fertilizer is not available to the plant, ie it is not absorbed by the plant. This is mainly due to soil P fixing processes. Thus, the adoption of the controlled release of phosphate fertilizer technology is advantageous in maintaining an optimal concentration of the nutrient over a longer period of time and thus avoiding nutrient losses to the medium. The use of natural polymers in combination with fertilizer becomes a good option and can improve the efficiency of fertilization. Among the most abundant natural polymers, lignin stands out as an interesting material for the development of controlled release fertilizers, and provides a new alternative of using this natural and renewable byproduct. Therefore, the objective of this study was to obtain phosphorus-based controlled release fertilizer (MAP), coated with clay, chitosan and kraft lignin at different concentrations. In addition, evaluate the formulations obtained for their ability to release phosphorus in water and analyze the final characteristics of fertilizers with and without coatings. For the preparation of the coated granules the immersion method was used to receive the lignin coating in different concentrations. The treatments were submitted to the controlled release test, in which the samples (5 g of MAP) were placed in containers containing 200 mL of distilled water at 30 °C and stored in a clearing chamber with a constant temperature of 30 °C. Aliquots were withdrawn at 10, 20, 30, 60, 120 and 180 min. Thermogravimetric analysis, infrared spectroscopy (FTIR), elemental analysis and scanning electron microscopy (SEM) were also performed. The addition of the coating and the increase in the lignin concentration used reduced the amount of apparent pores in the fertilizer by filling the voids in the surface of the granules which reduced the porosity of the granules. Subsequently, in the test for the release of phosphorus in water, the materials with 30% lignin coating (MAP2, MAP3 and MAP4) presented higher results than MAP with lignin coating at 4% (MAP1) and without coating (MAP0). In all tests the treatments MAP2, MAP3 and MAP4 presented statistically equal results. With these results we conclude that lignin coating is efficient in reducing the release rate of P present in MAP.