Uso agrícola de resíduo da produção de ácido fosfórico (gesso) associado ao cloreto de potássio

Abstract

Searching for the use of industrial residues in agriculture has been, in the last few decades, a viable alternative to direct the rejects that, if stored improperly, may cause environmental contaminations. Agricultural gypsum is a residue produced in great quantities during the production of phosphoric acid, which is used to produce phosphate fertilizers, making it necessary to find an adequate destination for the residue. In this context, this paper aimed to verify the viability of using gypsum associated with the application of potassium, as a subsurface ground conditioner and in agricultural production. Three experiments were carried out in Fazenda Experimental do Instituto Federação de Educação, Ciência e Tecnologia do Triângulo Mineiro (IFTM), campus Uberaba, located in the city of Uberaba, Minas Gerais, on distrophic Red Latosol of medium texture, using the culture of cauliflower, corn and sorghum, in a 5x5 factorial, being evaluated five doses of gypsum (0, 500, 1.000, 2.000 and 4.000 kg ha-1) and five doses of potassium (0, 100, 180, 240 and 360 kg ha-1) of K2O in completely randomized design. In all the cultures we evaluated: the chemical attributes of the soil on layers of 0-0.20 and 0.20-0.40 m; the nutritional state of the plants; and the productive and biometrical attributes. In addition, we verified the volume of heavy metals (Cd, Cr, Pb and Ni) in the agricultural gypsum, in order to check the risks of environmental contamination after the application of this residue in the soil. The application of agricultural gypsum brought significant improvements in the volumes of calcium and sulfur on layers of 0-0,20 and 0.20-0.40 m of the soil in all evaluated cultures, which allowed the increase of Ca and S leaf volume in the cultures of corn and sorghum. However, the productivities of corn and sorghum were not influenced by the evaluated factors. There was a significant decrease in the values of potential acidity and in the volumes of Al in the soil, after the culture of corn, due to the application of gypsum. The plant height and the stem diameter in the culture of sorghum decreased linearly with the increase of gypsum application. Significant interactions between the doses of gypsum and K for the characteristics diameter of the peduncle and head height in the culture of cauliflower were verified, as well as for the volume of total soluble solids (ºBrix) in the culture of corn, in which we verified a proportional increase in its measures with the application of gypsum. The analysis of the heavy metals Cd, Pb, Cr and Ni highlighted traces of 0.004% for the volume of Cd in the sample of agricultural gypsum, pointing out the viability of the application of high doses of this residue as a soil conditioner in agriculture.