Transformation of Iron and Manganese in Coastal Saline Soil

The changes in the forms of iron and manganese and the redox potential of soil were studied under submerged condition of coastal saline soil of West Bengal. There was a very sharp fall in redox potential of soil from +555mV to +210 mV within 4 days of submergence. The submergence of the soil also caused significant increase in both soluble and exchangeable forms of iron and manganese. An increase in soluble and exchangeable Fe and Mn with decrease in the redox potential in the beginning followed by a reversal of these processes after about 20 days were noticed. Addition of organic matter enhanced the initial decrease in redox potential and the increase in soluble and exchangeable Fe²⁺ and Mn²⁺ in soil. This effect was more prominent when undecomposed organic matter (powdered rice straw) was added instead of well decomposed material like farmyard manure.