Evaluation of different zinc sources for lowland rice production

ZnSO4, Zn-enriched farmyard manure (Zn-FYM), Zn-tetraammonia complex sorbed on FYM [Zn(NH3)(4)-FYM] and Zn-ethylenediaminetetraacetate (Zn-EDTA) were compared as Zn sources for rice production under lowland conditions. The amount of Zn supplied by Zn-EDTA was one-tenth of that supplied by the other Zn sources. Zn application to a Zn-deficient soil corrected the visual symptoms of Zn deficiency and significantly increased the total biomass, grain yields and the harvest index of rice, as well as the Zn concentration in the grain and the uptake of Zn by the straw and the grains. Even with lower rates of application (0.25 and 0.5 mg Zn kg(-1) soil), Zn-EDTA treatments gave comparable values for these parameters, and the highest "Zn-mobilization efficiency" compared to the other Zn sources. The content of diethylene-triaminepentaacetate (DTPA)-extractable Zn in the soil of the different treatments after the harvest of rice was in the order; ZnSO4 = Zn-FYM>Zn(NH3)(4)-FYM = Zn-EDTA. The application of Zn also significantly increased the number of panicles that emerged between 80 to 93 days after transplanting, though the total number of panicles at harvest remained unaffected. The calculated panicle-emergence index had a positive correlation with the grain yield of rice. The Z(n)-EDTA treatment, inspite of supplying the lowest amount of Zn, as well as leading to the lowest rate of Zn uptake, produced the highest yields. Therefore, we concluded Zn-EDTA to be the most efficient source of Zn for lowland rice production.