抄録
pH of soil water change with addition of acid solution is a complex physicochemical process. In this study repetitive addition of acid solution experiments were combined with chemical equilibrium model to simulate pH change for Allophanic soil. pH of soil water after added nitric acid solution was decreased rapidly than that of sulfuric acid solution. After three to six times repetitive addition of pH 2 nitric and sulfuric acid solution pH was held as constant in both solutions due to buffering capacity of mineral weathering. Ion activities and ion-pair concentrations were calculated to determine the constant of aluminum solubility and sulfuric ion sorption isotherm. Aluminum solubility in nitric acid solution was large compared with that in sulfuric solution. Sulfuric ion adsorption was described well by Langmuir equation. Simulation model of pH in equilibrium soil water were composed of aluminum dissolution, formation of the three aluminum species, aluminum-dominant divalent base cations exchange, bicarbonate formation, sulfuric ion adsorption, charge balance and mass balance of sulfuric ion and base cations respectively. Buffering capacities due to weathering of minerals were not negligible. Then, aluminum-base cations exchange were lumped together with mineral weathering as neutralization effects in the model. pH of soil water could estimate with standard error less than 土pH 0.2 by this model.
