Sulfur and zinc availability from co-granulated Zn-enriched elemental sulfur fertilizers

Abstract

Acidification by oxidation of elemental sulfur (ES) can solubilize ZnO, providing slow release of both sulfur (S) and zinc (Zn) in soil. For this study, a new granular fertilizer with ES and ZnO was produced and evaluated. The effect of incorporating microorganisms or a carbon source in the granule was also evaluated. Four granulated ES–Zn fertilizers with and without S-oxidizing microorganisms, a commercial ES pastille, ZnSO4, and ZnO were applied to the center of Petri dishes containing two contrasting pH soils. Soil pH, CaCl2-extractable S and Zn, and remaining ES were evaluated at 30 and 60 days in two soil sections (0–5 and 5–9 mm from the fertilizer application site). A visualization test was performed to evaluate Zn diffusion over time. A significant pH decrease was observed in the acidic soil for all ES–Zn fertilizer treatments and in the alkaline soil for the Acidithiobacillus thiooxidans-inoculated treatment only. In agreement with Zn visualization tests, extractable-Zn concentrations were higher from the point of application in the acidic (62.9 mg dm–3) compared to the alkaline soil (5.5 mg dm–3). Elemental S oxidation was greater in the acidic soil (20.9%) than slightly alkaline soil (12%). The ES–Zn granular fertilizers increased S and Zn concentrations in soil and can provide a strategically slow release of nutrients to the soil.