ACCUMULATION OF SOME METALS BY LEGUMES AND THEIR EXTRACTABILITY FROM ACID-MINE SPOILS

A greenhouse study was conducted to investigate the growth (dry matter yield) of selected legume cover crops; phytoaccumulation of metals such as Zn, Mn, Pb, Cu, Ni, and Al; and extractability of heavy metals from three different Alabama acid mine spoils. The spoils were amended based on soil test recommended levels of N, P, K, Ca, and Mg prior to plant growth. Metals were extracted by three extractants (Mehlich 1, DTPA, and 0.1 M HCl) and values correlated with their accumulation by the selected legumes. Among the cover crops, kobe lespedeza [Lespedeza striata (Thung.) Hook & Arn.], sericea lespedeza [Lespedeza cuneata (Dum.) G. Don], and red clover (Trifolium pratense L.) did not survive the stressful conditions of the spoils. However, cowpea (Vigna unguiculata L.) followed by 'Bragg' soybean [Glycine max (L.) Merr.] generally produced the highest dry matter yield while accumulating the largest quantity of metals, except Al, from spoils. The extractability of most metals from the spoils was generally in the order of: 0.1 M HCl > Mehlich 1 > DTPA. Mehlich 1 did not extract Pb and 0.1 M HCl did not extract Ni, whereas DTPA extracted all the metals in a smaller amount relative to HCl and Mehlich 1. All the extractants were quite effective in removing plant-available Zn from the spoils. In general, the extractants' ability to predict plant-available metals depended on the crop species, spoil type, and extractant used.