Appraisal of some soil tests for zinc availability to late-sown wheat grown in Mollisols

Five soil extractants, namely, 0.005M diethylene triamine pentaacetic acid (DTPA) (pH 7.3), 0.005M DTPA + 1M ammonium bicarbonate (pH 7.6), Mehlich 3, 0.01M ethylene diamine tetraacetic acid (EDTA) + 0.05M ammonium carbonate (pH 8.6), and 1M magnesium chloride (MgCl2) (pH 6.0), were evaluated to predict the response of wheat to zinc (Zn) application in Mollisols. These extractants could be arranged in the following decreasing order of their Zn extracting power: Mehlich 30 > 0.005 M DTPA + 1M ammonium bicarbonate > 0.01 M EDTA + 0.05M ammonium carbonate > 0.005 M DTPA > 1MMgCl(2). The critical limits of Zn in soil, below which the yield response to late sown wheat (var. UP-2338) to Zn application could be expected, were 0.57 mg 0.005M DTPA (pH 7.3) extractable and 1.72 mg Mehlich 3-extractable Zn kg(-1) soil. The critical limit of Zn in whole shoot at 60 days after emergence was found to be 26.1 mg Zn kg(-1) plant tissue. The DTPA and Mehlich 3-extractable soil Zn also correlated significantly and positively with Zn concentration in whole shoot at 60 days after emergence and total Zn uptake by wheat at harvest.