Chemical Forms of Residual Zn as Affected by Zinc Sulfate in Some Mazandaran Prov. Soils

This experiment was conducted to study different chemical forms of Zn (native and applied Zn) in some selected paddy soils of Mazandaran. Twenty soil samples with the widest range of physicochemical properties, especially with respect to the levels of available Zn and P, were selected out of some 40 surface soils (0-30 cm) collected in rice paddies of east Mazandaran. A completely randomaized block factorial experiment (20×2) with two levels of Zn (0 and 10 µg Zn/g soil as ZnSO4.7H2O) and three replications was carried out on the 20 soils in the greenhouse. Different chemical forms of Zn i.e., exchangeable, sorbed, organic, carbonate, and residual were fractionated by 0.5M KNO3, XH2O, 0.5M NaOH, 0.05M Na2EDTA and 4M HNO3 extractants, respectively in order to determine the amount and chemical form of Zn fractions.The extracted Zn was determined by atomic absorption and ICP-AES instruments. The results showed that KNO3-Zn (exchangeable Zn) was determined as non detectable (ND) zinc. Total Zn, in untreated soils (native Zn) ranged from 49.3 to 84 µg/g with a mean of 63.4 µg/g. Distribution of native Zn in different soil chemical fractions were in the fallowing order: Residual >>> Carbonate> Organic> Sorbed> Exchangeable Most of the applied ZnSO4 was converted to residual and carbonate forms as much as 40.4 and 34.9 percent respectivily. Redistribution of Zn fractions as affected by 10 μg Zn/g soil were in the fallowing order: Residual > Carbonate> Organic> Sorbed> Exchangeable