The nature of acidity in selected acid soils

Abstract

Most of the soils in the eastern one-third of Texas are acid. To this date little work has been done to evaluate the acid status of these soils. The present effort was initiated to study total acidity and the contribution of the components to that acidity. Organic matter and acid sulfate minerals were among those components analyzed in order to determine their contribution to soil acidity. Total titratable soil acidity increases with increasing clay contents. A regression line with a slope of 0.37 and r² value of 0.62 indicated the clay constitutents of the various soils of this study had a direct influence on total acidity. Two kaolinitic soils, Katy and Hockley, showed a smaller increase in acidity with clay percentage than the other kaolinitic and smectitic soils probably due to the presence of relatively more kaolinite. The kaolinitic-smectitic, Cuthbert, and other smectitic soils (Beaumont, Falba, Sacul and Aubrey) increased in acidity with increasing clay content at a higher level than the kaolinitic soils. Correlation between the clay of these soils and nonexchangeable acidity was 0.72. However, correlation between 2:1 clay minerals and non-exchangeable acidity was poor (r² = less than 0.19). Total non-exchangeable acidity was higher in the A horizons than the B and C horizons in all soils. Pyrophosphate extraction and titration methods indicated that the hydroxy A1 (non-exchangeable acidity) was easily removed in the Beaumont, Sacul and Aubrey surface soils..