Within the last three decades, the rice-wheat cropping system has triggered, and with time, aggravated soil micronutrient deficiencies in the Indo-Gangetic Plains (IGP). This has largely been due to the shift from an earlier rice and wheat monoculture with low yielding, long duration indigenous varieties, to an intensive rice-wheat rotation cropping system with short duration modern high yielding varieties on the same piece of land. The problems related to micronutrient deficiency in the IGP are more due to the size of its available pools in the soil rather than its total contents and are greatly influenced by crop management, or rather its mismanagement. Deficiency of zinc is widespread in the IGP, but with the extensive use of zinc sulfate, zinc deficiency has reduced in some areas of the region. Meanwhile, the deficiency of Fe, Mn and B has increased in the IGP. Deficiency of Cu and Mo is location specific and can limit rice and wheat yields. The adoption and spread of the rice-wheat system in permeable coarse textured soils, particularly in the western IGP, not only caused iron deficiency in rice but also resulted in the emergence of manganese deficiency in wheat. In highly calcareous and acidic soils, boron is the next limiting micronutrient in
The sorption of low concentrations of cadmium by the calcium-saturated <2 �m fraction of four soils was studied in the presence of variable concentrations of calcium and zinc, as a model of reactions in contaminated soils. The sorbed cadmium and zinc was determined by radioisotopic procedures and partitioned experimentally into specifically and non-specifically sorbed forms. With cadmium the non-specifically sorbed form usually exceeded specifically sorbed. Specific sorption of cadmium was depressed by competition with zinc but not the reverse. The non-specifically sorbed component of sorbed cadmium, as defined by rapid exchange with calcium nitrate solution, was preferred over calcium by the clay exchanger, with separation factors of 4-10 for cadmium saturations of <1% CEC. Some implications for the management of soil as a sink for heavy metal pollutants are discussed.
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