EXTRACTABLE ZINC AND MANGANESE AS RELATED TO APPLIED CADMIUM IN CONTRASTING INDIAN SOILS

Soil chemical interaction of applied cadmium (Cd) and native zinc (Zn) and manganese (Mn) was studied in four contrasting Indian soil types, namely, an ultisol, an alfisol, an entisol and a vertisol with and wi thout sewage sludge amendment. The soils after incubation periods up t o 16 weeks were sequentially extracted with 0.5 M KNO3, deionised wate r, 0.5 M NaOH, 0.05 M Na(2)EDTA and 4 M HNO3; these extracted fraction s represent the exchangeable, adsorbed, organic-bound, carbonate and s ulfide/residual forms of Zn and Mn, respectively. Results indicated th at in both Cd-treated and Cd-enriched sludge treated soils very small amounts of plant-available Zn could be extracted and the sulfide/resid ual fraction was the predominant Zn fraction extracted throughout the incubation period of 16 weeks. High amounts of organic-bound Zn presen t in sewage sludge were transformed into sulfide/residual or bound for ms during the incubation period. Data on the extraction of Mn from dif ferent Cd- and Cd-enriched sludge treated soils revealed that high amo unts of exchangeable Mn were extracted in ultisol and alfisol througho ut the period of 16 weeks of incubation, indicating its presence in pl ant-available forms for a longer period of time in these two soil type s. In the case of entisol and vertisol, the extraction pattern was ver y much different and only very small amounts of plant-available Mn cou ld be extracted, possibly due to the higher pH, cation exchange capaci ty and silt/clay loam texture of these soils.