Adaptation of Calcium Acetate Methodology to Determine the Potential Acidity of Tropical Soils

ABSTRACT

The determination of potential acidity (H+ Al) is of great importance to assess of the degree of soil fertility because of its direct application in the calculation of the cation exchange capacity. However, the direct method of determining H+ Al presents several problems, such as inaccuracy of titration and long time to perform the analysis. Our objective was to optimize the calcium (Ca) acetate method to make it faster, more accurate and capable of being applied on a large scale in routine analysis. The simplified method to obtain the value of H+ Al was based on reading the pH after extraction with Ca acetate, without the need for titration with sodium hydroxide. The contents of H+ Al were obtained in soil samples with varying contents of organic matter (OM) and H+ Al after extraction with either 0.5 mol L⁻¹ Ca acetate or Shoemaker, McLean, and Pratt (SMP) buffer solution. The extraction of H+ Al was affected by the nature and concentration of the extraction solution, and OM contents in the soils. The simplified method of calcium acetate was able to predict the levels of H+ Al in the soil and has a high potential to be used on a large scale in laboratories.

KEYWORDS:

• Buffer solution
• aluminum
• soil analysis
• hydrogen