Comparação de métodos de determinação do calcário residual no solo

Abstract

Correcting soil acidity by liming is necessary in the Cerrado region, as important nutrients become more available for crops, promoting increased productivity. The depth of action of surface lime to correct soil acidity varies with product dosage and particle size, application form, soil type, climatic conditions, cultivation system and time after application. In this sense, the determination of the non-exchangeable fractions of Ca and Mg in the soil, which theoretically represents the fraction of the remaining limestone (“residual limestone”) that has not yet been dissolved in the soil, combined with the chemical characteristics contained in the fertility analysis. It can be an important tool to help determine when limestone needs to be reapplied in a no-till system. The general objective was to compare the estimation of residual limestone (unreacted limestone) obtained by the method with hot HCl and KCl with tube percolation, in soil samples, trying to evaluate conditions for the optimization in order to increase the practicality in routine determinations. The study was conducted at CPMUA - Federal University of Mato Grosso (UFMT), Campus Universitário do Araguaia, Barra do Garças - MT, with soils collected from two grain-producing farms and native forest, with two known limestone levels in each condition. The methods were the use of 1 M KCl with percolation in the tube (Sample of 10 cm3 of soil on an adapted mechanism with filter paper and beaker), the determination of residual limestone in the soil was carried out after filtering together prepared with an adapted percolation tube , placing 10 cm3 of soil between filter papers and then 100 mL of KCl solution, which form infiltrates in the sample (for the first extraction of Ca and Mg), in the second extraction (residual limestone) it was tested two variations of the method, the one using 0.5N HCl, hot for ten minutes and the one with 0.8N HCl for 5 minutes). Significance of the interaction between methods and conditions of the soil collection sites was observed, both for Ca and Mg contents, so the conditions of residual limestone determination in the laboratory can influence the analytical determinations according to the place of origin of the samples of soil. Therefore, non-exchangeable Ca and Mg contents by the 0.8 M HCl and 0.5 M HCl method can be used to estimate the amount of limestone remaining in the soil.