Differentiation Between the pH Effect and the Bicarbonate Ion Effect in Causing Lime-Induced Chlorosis

Lime-induced chlorosis has been recognized for many years as a problem where plants are grown on calcareous soils. There are many factors associated with and influencing this form of iron chlorosis and because of this it has been very difficult to determine the relationship between the factors and chlorosis. There are high concentrations of bicarbonate in calcareous soils. Because of this high concentration, it was believed that the presence of the bicarbonate ion was causing chlorosis. It has been proposed that the pH of the growth medium was the causitive factor of lime-induced chlorosis. Most calcareous soils have a pH range around 8.0. At this pH the solubility of iron is very low, and it was believed that chlorosis was a result of iron being insoluble at a high pH. Iron chlorosis has been induced in plants by increasing the phosphorus concentration in the growth medium. Iron phosphates have a low solubility and it was believed that the available iron was precipitated by the phosphates. The interference of metals such as calcium, nickel, cobalt, zinc, and copper appears to be a factor affecting the absorption of iron by plants. It was thought that an interfering ion (Ni, Co, Ca, Zn) may interfere with the translocation of iron in the malic or malonic acid complexes (Tiffin and Brown, 1962)