Comparison of four different extraction methods to assess plant availability of some metals in organic forest soil

The objective was to find an uncomplicated test giving the best correlation between calcium (Ca), magnesium (Mg) manganese (Mn), copper (Cu), zinc (Zn), and lead (Ph) extracted from humic forest soil and the total concentration of the element in some understorey forest plants using well-known extractants. The elements were selected because Ca, Mg, Mn, Cu, and Zn are essential nutrients to plants and Zn and Pb are potentially harmful heavy metals received over the years in the southern parts of Norway by long-range atmospheric transport. Extraction of organic podzolic surface soil (Oe and Oa horizon) from 17 different pine forests in central and southern Norway was carried out with four different reagents to evaluate uptake of Ca, Mg, Mn, Cu, Zn, and Ph in the understorey plants Deschampsia flexuosa, Vaccinium myrtillus (leaves and stems), and Vaccinium vitis-idaea (leaves and stems). The NH4OAc, NH4NO3, HCl, and EDTA solutions used to extract the soil in addition to concentrated HNO3, demonstrated variability in capacity to extract the different elements from the soil. The extractants yielded significant relations between concentrations of Ca, Mn, and Ph in the Oe or Oa horizon and some of the plants or plant compartments, even though distinct correlation was more dependent on species and plant part than the actual extractant used. In the case of Zn, Cu, and Mg only a few sporadic correlations were observed between the different plant/plant compartments and the element concentrations in the soil extracts. Altogether none of the extractants was shown to be superior to the others in providing the best correlation with the elements concentrations in selected plant/plant compartments. In the case of Ca, Mn, and Ph all the extractants including concentrated HNO3 provided significant correlations with at least some of the selected plant/plant compartments.