Distribution and Transformation of Zinc Fractions from Zinc Sulfate Coated Urea Fertilizer on Three Rice Soils.

Zinc deficiency in mid-southern rice production is commonly ameliorated with surface broadcast applications of granular zinc sulfate (ZnSO₄). A drawback to using ZnSO₄ is the rate of ZnSO₄  fertilizer that must be used to evenly distribute Zn across the field. Zinc sulfate coated urea fertilizers (ZSCU) are manufactured to improve nitrogen use efficiency but may also improve Zn spatial distribution and change the soil fractions of Zn as the Zn is released into soil solution. Limited research exists on the Zn release rate from ZSCU or the distribution and transformation of ZnSO₄ coated urea after application. The objectives of this study were to (i) determine the Zn release rate from experimental ZSCU and (ii) evaluate the distribution and transformation of Zn fractions 7, 15, 30 and 60 d following application of ZSCU. Zinc release from ZSCU was examined for three rice soils using the kinetic batch method with 0.01 M CaCl₂. Zinc was applied to 1g of soil at a rate of 60 mg Zn kg^-1. Treatments were replicated three times. A completely randomized design was used to evaluate fractions of Zn in three soils at different times after application. Zinc was surface applied as either zinc sulfate or ZSCU at 80 mg Zn kg^-1. Zinc fractions were analyzed for water soluble, exchangeable, Mn-oxide soluble, organic soluble, Fe-oxide soluble and residual Zn at 7, 15, 30 and 60 days after fertilization. The release and distribution of Zn from both ZSCU and ZnSO₄was influenced by soil properties including pH, CEC and clay content. Soil extractable Zn fractions in increasing order was water soluble < exchangeable < Mn-oxide soluble < organic soluble < Fe-oxide soluble < residual.