Speciation of Fluid- and Granular-fertilizer Derived Cu and Mo in a Calcareous and an Acid Soil using Micro- X-ray -Fluorescence, and -Absorption.

The major reason for the widespread occurrence of micronutrient deficiency in soils is due to the low availability of micronutrients to plant roots rather than a low concentration present in soil.  Previous experiments using isotopic dilution techniques to investigate the diffusion and potential availability of Cu and Mo from different fertilizer sources in different Australian soils revealed that granular Cu and/or Mo did not move away from the point of application or did not remain exchangeable in and around point of application compared to fluid fertilizer forms. This research aimed to investigate how different forms of Cu and Mo react in a calcareous and an acid soil at the molecular level using the micro-scale spatially-resolved synchrotron techniques; namely micro-x-ray fluorescence and micro-x-ray absorption. We hypothesized that the differences in the effectiveness between granular and fluid-Cu and -Mo fertilizers may be due to different Cu/Mo reaction processes in and around fertilizer granules and fluid fertilizer bands.  Micro-XRF mapping of soil:fertilizer reactions zones indicated that diffusion of Cu, and Mo from fluid fertilizers was greater in comparison to Cu or Mo from granular fertilizers in both soils after 4 wk of incubation.  Further differential diffusion behavior of fluid and granular fertilizers of Cu and Mo appeared to be somewhat influenced by inherent soil pH.  Results examining the differences in fertilizer reaction products identified using x-ray absorption spectroscopy will also be presented.