Toxic Metals in Acid Soil: II. Estimation of Plant-Available Manganese
1971
Hoyt, Paul B. | Nyborg, M.
Manganese in 40 acid surface soils was measured by eight methods and statistically compared with the concentrations of Mn in barley (Hordeum vulgare L.), turnip rape (Brassica campestris L.), and alfalfa (Medicago sativa L.) grown on the soils in a greenhouse study. Of the eight methods, a 16-hr extraction with 0.01M CaCl₂ gave by far the best estimate of plant-available Mn, the correlation coefficients being 0.76, 0.73, and 0.86 between Mn extracted from the soil and the concentrations of Mn in barley, rape, and alfalfa, respectively. Another form of soluble Mn, that extracted by 0.1N HOAc, gave the next best estimate of plant-available Mn. The other five extraction methods, consisting of 0.1N H₃PO₄ or 0.002N HCl for soluble Mn, 1N KCl or 1N NH₄OAc (pH 3) for exchangeable Mn, and 0.2% hydroquinone in 1N NH₄OAc (pH 7) for easily reducible Mn, gave fair to poor estimates of available Mn. Total Mn gave a poorer estimate than did any of the methods used for extractable Mn. On arranging the soils in two groups of equal number, having pH ranges of 4.15–5.14 and 5.15–5.63, good measurements of available Mn in both groups were given by only the 0.01M CaCl₂ method. Manganese in the three plant species was correlated with soil pH but not with percent base saturation. Besides being related negatively to soil pH, Mn in the plants also was related positively to total soil Mn and negatively to soil exchange capacity as shown by multiple regression analyses.
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