The effects of soil organic matter levels on soil solution concentrations and extractabilities of manganese, zinc and copper.

To determine the effect of soil organic matter on concentrations of metals in soil solution and their extractability from soil, solutions containing varying concentrations of Mn, Zn and Cu salts were added to five samples of a sandy loam soil with organic matter levels ranging from 0.8 to 2.4% C. Concentrations of the metals and their ions in solutions displaced from the samples after 3 weeks of incubation were determined. Extractabilities of the metals by both single extractants (EDTA and acetic acid) and by a sequential extraction scheme (calcium chloride, hydrogen peroxide, acetic acid and aqua regia), and release of the metals into solution as a function of pH were also studied. The total concentration of Mn, Zn and Cu in displaced solutions were almost independent of the organic matter status of the samples, but cupric ion concentrations were smallest in solutions displaced from samples with high organic matter content. The percentage of the total amount of each metal present in free ionic form in solution was , respectively. When EDTA and acetic acid were used as single extractants, extractability showed no discernible trend across the range of organic matter in the samples with no metal added. Acetic acid did, however, extract less of the Zn and Cu that was added to samples with more organic matter. There was no effect of organic matter status on the extractability of Mn. In the sequential extractions, smaller proportions of either native or added Cu were solubilised by calcium chloride from the samples with more organic matter than from others; also acetic acid extracted less of the added Zn and very much less added or native Cu from samples higher in organic matter. Conversely, hydrogen peroxide extracted higher concentrations of metals from samples with more organic matter than from others. In the study of effects of pH, smaller concentrations of Zn and Cu were extracted at every pH from the sample with the most organic matter than from the sample lowest in organic matter.

RESP-10167