The total acidity including residual and exchangeable acidity. Often it is calculated by subtraction of exchangeable bases from the cation exchange capacity determined by ammonium exchange at pH 7. 0. It can be determined directly using pH buffer-salt mixtures (e.g. BaCl2 plus triethanolamine, pH 8. 0 or 8. 2) and titrating the basicity neutralized after reaction with a soil.