Assessing the plant availability of manganese in soils using Diffusive Gradients in Thin films (DGT)

Abstract

Manganese (Mn) deficiency is a significant problem in crop production, but due to its redox instability there are presently no reliable soil tests available to predict the plant availability of this essential micronutrient. Recently, the Diffusive Gradients in Thin films technique (DGT) was shown to be superior to other existing methods in predicting plant availability for elements, such as Cu, Zn and P. However, DGT has not yet been applied to assess Mn availability. We deployed DGT devices in a range of different Scandinavian agricultural soils, equilibrated under different redox conditions. Manganese K-edge XANES spectra were also collected after the different treatments. The XANES spectra showed that anaerobic soil conditions caused the reduction of Mn(IV) and Mn(III) to Mn(II). Dynamics in Mn availability due to changing redox conditions were reflected by the DGT measurements. However, a poor and insignificant correlation between CDGT and plant tissue concentrations was found when soils were tested under aerobic conditions (r2=0.25). This correlation was significantly (p<0.01) improved by deploying DGT in anaerobically equilibrated soils (r2=0.60). Nevertheless, since the plant availability of Mn in soil is a highly dynamic process with major temporal fluctuations over a growing season, it is unlikely that the DGT techniques can be used to accurately predict the plant availability of Mn in crop production. However, this study shows that DGT is a powerful analytical tool, which can be used to provide novel information about the factors controlling availability of redox sensitive elements, such as Mn, in soil.