Reactivity of two acidity correctives in a medium texture soil

Abstract

For crops to have good productivity, it is necessary to adopt agricultural practices that ensure an adequate supply of water and nutrients, and neutralize toxic elements in the soil, especially exchangeable aluminum, both in the arable layer and in the subsurface. One of these agricultural practices usually employed in both small and medium and large rural properties is the correction of soil acidity, which aims, in addition to neutralizing exchangeable aluminum, to provide calcium and magnesium for plants. Several materials have been used to correct soil acidity, with carbonates, oxides, hydroxides or silicates as neutralizing components. In the present work, the reactivity of two acidity correctives was evaluated in a soil of medium texture, with high aluminum saturation: 72.96%. The correctives used were a steel slag (calcium silicate), and a dolomitic limestone, applied in doses equivalent to one, one and a half, two, and two and a half times the analytically predicted amount, to raise the base saturation to 60%, using calcium acetate with H+ + Al3+ extractor. The study also included a control treatment, which did not receive acidity correction. The method used to evaluate the reactivity of the two correctives was soil incubation. The block design was used, with six repetitions per concealer dose. The experimental units were plastic bags with 3.0 kg of soil. After mixing the correctives with the soil, in the doses corresponding to each treatment, they were transferred to plastic bags and incubated at 70% of the maximum water retention capacity for ninety days. After the incubation period, the soil was analyzed for pH in CaCl2, pH in H2O, exchangeable aluminum (Al+3), and base saturation (V %). Steel slag and dolomitic limestone had the same efficiency to neutralize aluminum and increase base saturation. The pH in CaCl2 and pH in H2O were highly correlated, with the average pH in H2O being 0.50 units greater than the pH in CaCl2. The equation to relate pH in CaCl2 to pH in H2O was Y= 1.0273 x + 0.4716, with R2 = 0.9730. Complete neutralization of Al+3 occurred when the soil pH was raised to 5.03 (pH in CaCl2) or pH 5.50 (pH in H2O). The extraction of H+ + Al3+ with calcium acetate resulted in an underestimation of the cation exchange capacity at pH 7.0 (CTC T), and consequently of the corrective dose to be applied. On average, there was a need to double the amount of concealer predicted analytically to reach the desired base saturation. The equation to relate base saturation with corrective doses, in CaCO3 equivalents, was Y= 9.1476x + 3.8439, with R2 of 0.9449.