Método alternativo para estimar a reatividade de corretivos de acidez do solo

Abstract

The reactivity of soil acidity correctives is an important parameter in liming calculations and is currently determined by the sieve method. Brazilian legislation considers only the particle size distribution of the correctives as a factor for estimating reactivity, disregarding the solubility of the parent rock of the materials. In this context, the objective of this study was to propose an alternative and complementary method for estimating reactivity, also taking into account the solubility of the correctives. Three experiments were conducted using five corrective materials (Material 1 – 44,23% CaO and 7,68% MgO; Material 2 – 31,73% CaO and 20,26% MgO; Material 3 – 55,58% CaO and 1,84% MgO; Material 4 – 34,62% CaO and 23,79% MgO; and Material 5 – 46,17% CaO and 13,44% MgO) and five particle size fractions (<0,297; 0,297–0,500; 0,500–0,840; 0,840– 1,000; and 1,000–1,700 mm). The first experiment was carried out in a laboratory at the Federal University of Uberlândia (UFU), campus Umuarama, where a chemical test was developed to estimate reactivity; the estimation was based on the volume of hydrochloric acid (HCl) consumed to maintain the solution with distilled water and the correctives at pH 6. The second experiment consisted of a 120 daysincubation test to evaluate reactivity through the increase in pH in water, pH in calcium chloride, calcium and magnesium contents, and the reduction of soil potential acidity. Finally, sorghum cultivation was evaluated in a greenhouse to verify the influence of correctives and particle sizes on crop development and soil chemical attributes; two sowings were carried out to compare soils with different chemical attributes and buffering capacity. The variables were subjected to analysis of variance, and when significant, the means were compared using Tukey's test (α = 0,05). The chemical test showed that, within the same particle size, materials presented different reactivities, and that finer particle sizes resulted in greater reactivity of the correctives. After the incubation test, it was inferred that particle size is an important factor for estimating the rate of action of correctives in the soil; however, other factors such as rock solubility, neutralizing power, and Ca and Mg contents can also affect reactivity. The interaction between materials and particle size influenced the Mg content in the soil (first sowing) and the Mg content in leaves (second sowing). Increases in foliar Ca and Mg contents, as well as in soil Mg, were proportional to the concentration of these elements in each material.