Visualization of Phosphorus and Zinc Diffusion From Fertilizers.

Nutrients applied to soil as fertilizer move away from the point of application mainly through diffusion. Sorption and precipitation reactions reduce the mobility of nutrients such as phosphorus (P) and zinc (Zn). The extent of diffusion of P and Zn in soil is usually assessed by laborious and destructive methods (sampling of soils in small sections) or through the use of radioisotopes (autoradiography) or synchrotron-based X-ray fluorescence microscopy. We developed a novel cheap method to visualize P and Zn diffusion from fertilizers in a simple and non-destructive way. Filter papers are impregnated with ferrihydrite (for P) or calcium carbonate (for Zn). The paper is placed on top of the soil in which a fertilizer granule or fluid fertilizer injection has been incubated for a given period. After a sufficient deployment period, the paper is removed and the P or Zn captured on the filter paper is visualized colorimetrically, using malachite-green for P or dithizone for Zn. We used this method to assess the effects of soil type, moisture content, fertilizer formulation and fertilizer additives on P and Zn diffusion from the fertilizer source. As the method is non-destructive, additional chemical measurements can be performed on the same samples. This method allows easy comparison of fertilizer sources and enables a better understanding of the physicochemical processes affecting fertilizer P and Zn behavior at the soil:fertilizer interface.