A field study on the influence of soil pH on trace element levels in spring wheat (Triticum aestivam), potatoes (Solanum tuberosum) and carrots (Daucus carota)

Soil pH is one of the main factors influencing the solubility and availability of trace elements in arable soils. Thus pH can affect the trace element contents of agricultural crops and thereby indirectly influence human health. The aim of this study was to determine Cd, Ni, Zn, Cu, Mn, Cr, Al and Se contents in spring wheat, potatoes and carrots (Cd, Ni and Zn) and estimate their correlations with certain soil factors (surface and subsurface soil pH and organic matter content) governing the plant availability of these elements. Commercial fields were sampled in Sweden in order to cover a wide range of soil types with respect to pH, soil texture and organic matter content. Concentrations of Zn, Mn, Ni (grain) and Cd (straw) in spring wheat (n=43); Cd, Ni, Zn,Mn, Cu and Al in potatoes (n=69); and Cd, Ni and Zn in carrots (n=36) showed significant negative correlations with surface soil pH (0-25 cm). The Se content of potatoes and Cr content of spring wheat straw were positively correlated with soil pH. Stepwise multiple regressions including a combination of soil pHs (0-25 and 25-50 cm) and organic matter contents (0-25 cm) showed that the organic matter content as well as the surface and subsurface soil pH significantly influenced concentrations of several trace elements in one or more of the studied crops. It was concluded that, if acid deposition together with other acidifying processes (fertilisation, harvest of biomass, etc.) are not balanced by a sufficient amount of liming there might be a decrease in the pH of arable soils, which, in turn will lead to decreased levels of Se in edible crops but an overall increase concentrations of other trace elements.