Determinação da acidez potencial de solos pela titulação direta

Abstract

The calibration of the solution SMP or the solution TSM for their use to estimate the soil potential acidity (H+Al) uses the direct soil titration by incubation with calcium carbonate for a period of 180 days, which makes the method laborious. Also, the extraction of potential acidity by calcium acetate is limited when the values of (H+Al) reach 7.0 cmolc Kg-1, or index TSM/SMP less than 5.5. Therefore, there is an alternative method of incubation with calcium hydroxide, which generates results in 5 days as well as shows similar data to the calcium carbonate. The objective of this study was to evaluate the soil incubation with calcium hydroxide and calcium carbonate, with calcium acetate extraction as methods for determining the soil H+Al. A total of 39 diverse soil types from whole Brazil was collected and a portion of 1 kg from each soil was incubated with calcium carbonate at 50, 75, 100, 125 and 150 % of potential acidity at pH 7.0, estimated by TSM and termed as "long incubation". As the "short incubation" consisted of portions of 40 g soil incubated for 5 days in an incubator at 30°C with calcium hydroxide solution in the same percentages of calcium carbonate but with addition of solid reagent of H+Al values above 8 cmolc Kg-1. We also carried the extraction of with 0.5 mol L-1 calcium acetate at pH 7.0 with 5 replicates of the samples. The results showed a positive correlation between the two incubation methods which indicates that it is possible to replace calcium carbonate incubation method with calcium hydroxide incubation to obtain the H+Al without compromising the interpretation of results.