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Abstract Understanding the effect of soil pH on the distribution of micronutrients among soil forms is a necessary precursor to designing micronutrient extractants that extract the form of the metal available to plants. An experiment was undertaken to determine effects of soil pH changes from different liming sources on the distribution of Mn, Cu, Fe, and Zn among soil fractions and to relate the amounts of micronutrients in the fractions to that extracted by the Mehlich I and DTPA extractants. A sandy soil was amended with rates of 0, 0.99, and 1.98 g kg −1 of three liming materials: calcitic limestone, dolomitic limestone, and an industrial by‐product containing 203 g kg −1 Mg. Following a greenhouse experiment, the soils were extracted with DTPA and Mehlich I and fractionated into exchangeable, organic, Mn oxide, amorphous Fe oxide, crystalline Fe oxide and residual fractions. The extracts and fractions were analyzed for Mn, Cu, Fe, and Zn, and there were very few differences among lime sources. Increasing lime rates decreased exchangeable Zn and increased organic fraction Zn and Mn. This increase in Zn and Mn in the organic fraction as pH is increased shows that pH does not influence metals in some fractions in the same manner as it does plant availability. Iron decreased in the exchangeable and organic fractions as pH increased. Correlations between DTPA‐ or Mehlich I‐micronutrients and those in the fractions were significant ( P = 0.05) only for the exchangeable and organic fractions. DTPA‐extractable Fe and Zn values were well‐correlated with plant uptake (0.842** and 0.377*, respectively). The results indicate that a micronutrient soil extractant should remove the exchangeable fraction but none of the oxide fractions and for Mn and Zn, none of the organic fraction.
L. M. Shuman (Mon,) studied this question.