Effect of soil pH on cation and anion solubility

Abstract

Abstract The effect of soil pH on the exchangeability and solubility of soil cations (Ca, Mg, Na, K, and NH4‐N) and anions (NO3‐N, Cl, and P) was investigated for 80 soils, spanning a wide range in physical and chemical properties and taxonomic groups. This information is needed from environmental and agronomic standpoints to estimate the effect of changes in soil pH on leachability and plant availability of soil nutrients. Soils were incubated with varying amounts of acid (H2SO4) and base (CaCO3) for up to 30 days. Although acid and base amendments had no consistent effect on cation exchangeability (as determined by neutral NH4OAc), amounts of water‐soluble Ca, Mg, Na, K, NH4‐N, and P decreased, while NO3‐N and Cl increased with an increase in soil pH. The increase in cation solubility was attributed to an increase in the negative charge of the soil surface associated with the base addition. The change in surface electrostatic potential had the opposite effect on amounts of NO3‐N and Cl in solution, with increases in N mineralization with increasing soil pH also contributing to the greater amount of NO3‐N in solution. The decrease in P solubility was attributed to changes in the solubility of Fe‐, A1‐, and Ca‐P complexes. The logarithm of the amount of water‐soluble cation or anion was a linear function of soil pH. The slope of this relationship was closely related (R2 = = 0.90 ‐ 0.96) to clay content, initial soil pH, and size of the cation or anion pool maintaining solution concentration. Although the degree in soil pH buffering increased with length of incubation, no effect of time on the relationship between cation or anion solubility and pH was observed except for NO3‐N, due to N mineralization. A change in soil pH brought about by acid rain, fertilizer, and lime inputs, thus, affects cation and anion solubility. The impact of these changes on cation and anion leachability and plant availability may be assessed using the regression equations developed.