Author : Weerapun Chotivanich

Summary : Twenty-four profiles and 40 surface soil samples were obtained from the major corn-producing regions of Thailand. The study aimed to evaluate the amount, distribution, and availability of micronutrient cations in the soils. As a consequence of the study an experiment was conducted to determine the form and method of zinc application for corn grown on zinc-deficient soils. As a consequence of the study an experiment was conducted to determine the form amd method of zinc (Zn) application for corn grown on zinc-deficient soils. The total amount of iron (Fe), manganese (Mn), zinc (Zn), and copper (Cn) varied from 1.60 to 12.60 percent, 110 to 6175 ppm, 12 to 87 ppm, and 14 to 180 ppm, respectively. Diethylene triamine penta acetic (DTPA) extractable Fe, Mn, Zn, and Cu ranged from 0.40 to 66.00, 0.20 to 68.00, 0.14 to 4.74 and 0.20 to 11.62 ppm, respectively. Available Fe in the soil profiles increased with the increase in CEC and available Mn increased with increase in organic matter the increase in either organic matter or CEC. Available Cu had no correlation with other soil characteristics. In general, the total quantities of these elements were relatively uniformly distributed throughout the soil profiles but their available forms decreased with depth. The double pot technique for diagnosing micronutrient deficient soils was used with corn (Zea mays L.) as test plant. The critical levels for corn using the sufficient quocient (SQ) procedure were 0.841 for Fe, 0.692 for Zn, and tentatively 0.81 for Mn and 0.82 for Cu. The SQ compared favorably with visual deficiency symptoms and the DTPA soil test. This method was found handy, cheap, and simple. Zinc application significantly increased the dry weight of corn planted in zinc-deficient soils. Commercial sources of zinc were Zn solution.