Department of Plant Sciences

Problems with Mn deficiency are significant in global crop production. Attempts to assess the plant availability of Mn have been impeded as it is highly redox sensitive and can be present in soil in a variety of chemical species having very different plant availability depending on the soil conditions. The Diffusive Gradients in Thin-films (DGT) technique is one of the most promising techniques for assessing plant nutrient and contaminant availability in soils. We tested the possibility of using DGT to assess Mn availability in soils under different conditions relevant to agricultural crops. It was found that it worked perfectly at pH 4 to 6 in model solutions with Mn concentrations relevant to agricultural soils. When different concentrations of competing cations (Ca, Mg, and Fe) were added at pH 6.5 the DGT still worked satisfactorily, but there were some indications that the highest concentrations influenced the DGT adsorbtion of Mn. Synchrotron analysis showed that Mn(II), which is the most prevalent oxidation state of Mn, was depleted in the soil when exposed to the DGT. Different soil deployment time showed that the DGT was able to register differences in plant availability caused by redox changes. Thus, our results suggest that the DGT technique may represent an efficient and reliable way of getting information on the plant availability of Mn in agricultural soils. Furthermore, the DGT technique appears to be a strong tool to assess the mechanisms controlling Mn availability in soil, including the redox potential and availability of carbon.