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

Forty bulk soil samples have been collected in paddy fields in eastern part of Mazandaran. Twenty soil types have been selected based on different phsico-chemical soil properties in terms of available phosphorus and zinc that had a wide range of soil test level. A factorial experiment (20×2) have been arranged as completely randomized block design with 3 replication including 2 levels of Zn (0 and 10 µg/g as ZnSO4, 7H2O), and 20 soils. A greenhouse experiment has been carried out in plastic pot in 2002. Different chemical forms of Zn such as exchengable, absorbed, organic, carbonate, and residual have been fractionated by Sposito method. Results showed that KNO3-Zn ( Exchengable Zn ) was the beyond detection limit of A.A ( Atomic Absorption) that was determined as non detectable (ND) zinc. Absorbed Zn of nontreated soils ( native Zn ), ranged from 0.06 to 0.82 µg Zn/g soil. Zn application increased mean absorbed Zn level and relative Zn percentage from 0.34 µg Zn/g soil and 0.7 percent in control to 0.49 µg Zn/g soil and 0.7 percent in the samples that was treated with10 µg Zn /g soil respectively. Native organic Zn content of soils ranged between non detectable (ND) to 1.7 µg Zn/g soil ( mean = 0.51 µg Zn/g soil). Mean and relative organic Zn increased 0.51 µg Zn/g soil and 0.8 percent in control to 0.96 µg Zn/g soil and 1.4 percent in the samples that was treated with 10 µg Zn /g soil. Carbonate Zn of non-treated soils ranged from 4.8 to 21 µg Zn/g soil ( mean = 0.51 µg Zn/g soil). Mean zinc content of carbonate Zn form has been increased 9.4 µg Zn/g soil in control to 12.9 µg Zn/g soil as influenced using 10 µg Zn/g soil treatment. Residual fraction of Zn content in non-treated soils ranged from 40.1 to 77.7 µg Zn/g soil (mean= 53.17 µg Zn/g soil and relative percentage = 83 percent ). Mean content residual has been up to 57.3 µg Zn/g soil while relative level of residual fraction has been decreased by 79 percent using 10 µg Zn/g soil treatment. Consequently ,distribution of native Zn in different soil chemical fractions are as fallow: Residual > Carbonate Organic Adsorbed Exchengable Redistribution of Zn fractions as affected by 10 µg Zn/g soil are as fallow: Residual Carbonate Organic Adsorbed Exchengable