pH variation in soil of three different land use: use of two pH methods

Abstract

Soil pH falls among the main soil quality parameters and is the primary factor in determining the productivity of the soil through its regulation of soil nutrient availability, aggregate stability and microbial activity. The ability of soil to withstand changes in pH from both natural and human perturbations is primarily a function of the acid neutralization capacity in the soil, the dominant clay mineralogy and soil organic matter (SOM) content (AMACHER and O NEIL 2007) where SOM serves as a major reservoir for terrestrial carbon (SCHLESINGER 1991). The total acidity of a soil can be divided in three pools: (1) active acidity, a measure of the H+ activity in the soil solution at a given time; (2) salt-replaceable acidity, which indicates the hydrogen and aluminum that are easily exchangeable by other cations in an unbuffered salt solution and (3) residual acidity. Active acidity is measured by extraction of the soil with deionized water (water pH) and saltreplaceable acidity is measured in a solution of 0.01M CaCl2 (salt pH). It is know that salt pH values are lower than water pH, because of the calcium in the salt solution displaces H+ ions sorbed to soil particles into solution (AMACHER and O NEIL 2007; NRCS 2004). pH measurements with CaCl2 solution diminishes the seasonal variation of pH by providing Ca2+ ions that displace the hydronium and aluminum ions and also reduce the seasonal effect of soluble salt concentration (NRCS 2004). The aim of our study was to compare pH variation using two methods:extraction with deionized water and extraction with calcium chloride in soil of three different land use: pasture, forest and tillage soil. The differences in pH values by two methods and in different soil will be further discussed in the presentation.