ZINC BUFFER CAPACITY OF VERTISOLS

The soil Zn buffer capacity is an important factor that regulates the concentration of plant-available Zn in soil solution. It is measured variously as Zn buffer power, Zn sorption or Zn desorption capacity. This study was conducted to determine Zn buffer power, and Zn sorption capacity and Zn desorption capacity in Vertisols as influenced by soil properties. The Zn buffer power, defined as the slope of the line relating soil solution Zn concentration to DTPA-extractable Zn, varied from 217 to 790. Soil pH was found to be the major soil parameter responsible for the variation in Zn buffer power. The sorption of Zn by these Vertisols was satisfactorily described by the Freundlich equation. The calculated values of the Freundlich parameters were closely related to the soil pH and amorphous Al and Fe content. Desorption of Zn by a series of successive extractions with DTPA was described by the Mitscherlich equation. The calculated values of desorption capacity were negatively correlated with soil pH and positively correlated with the contents of Al and Fe oxides. Work published elsewhere showed that the parameters of both the Zn buffer power and Zn desorption capacity accounted for as much as 62% of the variation in relative yield of wheat from Zn application to Vertisols.