Lability of Metallic Micronutrients in a Residual Peat Soil Amended with Calcitic Limestone
Residual peatland sites are of great biological interest and the risk of mobilization of high amounts of metallic trace micronutrients should be assessed. For this, soil incubations under controlled conditions have been carried out, in order to quantify two chemical fractions of four essential metallic trace elements in relation to the addition of calcitic limestone. Surface soil samples (mineral layers rich in organic matter) were collected from the Lamèque-Portage residual peatland site in New Brunswick (Canada). Several portions (200 g) of soil amended with three rates of calcitic limestone (0 g, 10.87 g and 14.5g) were incubated in a temperature-controlled growth chamber (25°C) for 0 to 150 days. Each treatment was replicated two times. After each incubation time, soil samples were air-dried and analyzed for pH. A two-step sequential extraction was applied to soil samples for the determination of "exchangeable" (readily labile) and "carbonate-bound" (moderately labile) metallic micronutrients (Cu, Fe, Mn and Zn). Analysis of the extracts was carried out by flame atomic absorption spectrometry. The results showed that the effect of limestone on the labile forms of metallic micronutrients is time-dependent. In general, there was a highly significant effect (P<0.001) of limestone application rate on labile forms of metallic micronutrients. Application of calcitic limestone, irrespective of the rate used, markedly reduced the labile forms of metallic micronutrients compared to the control. The content of labile Cd and Pb in limed soil was very low. These results may have practical implications in phytomanagement of residual peatland sites for bioenergy plant production.
Keywords - Heavy Metal, Trace Element, Speciation, Liming.