Department of Soils, Punjab Agricultural University, Ludhiana, Punjab, 141004
*Present address: Department of Soil Science and Agricultural Chemistry, Rajendra Agricultural University, Pusa, Samastipur, Bihar, 848125
The solubility of iron, manganese, copper and zinc in calcareous soils was determined by modified DTP A equilibrium method which enables the simultaneous measurement of the solubility of the micronutrient cations. Soluble hydroxy ions of Fe were found to increase the total metal ion activity several fold over Fe3+ activity in equilibrium with ferric oxides and hydroxides. The hydroxy ions of Cu and Zn could enhance their net activity up to the exetnt of 10 to 100 times over the Cu2+ and Zn2+ activities in soil solution. A concept of Fe ion buffer system likely to regulate the activities of Fe3+ ionic species is proposed. Complexing of metal ions by natural organic ligands seems to exert a profound influence on their pH dependent solubility as is evident from a significant correlation between the activities of these metal ions and organic carbon content of the soils.
Solubility, calcareous soils, DTPA, hydroxy metal ions, metal ion buffer
