Roslyn Baird

Sulfur and Zinc Availability from Co-granulated Zn-Enriched Elemental Sulfur Fertilizers

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.

Erratum to: Availability of fertiliser sulphate and elemental sulphur to canola in two consecutive crops

Aims We compared elemental sulphur (ES) and sulphate fertilisers in terms of yield and S uptake. Methods Two consecutive canola crops were grown on S-labelled soil amended with ammonium sulphate, ES-bentonite pastilles (90 % ES), or S-fortified ammonium phosphate (NP) fertilisers containing both sulphate-S and ES (5–8 % ES). The shoot yield, S concentration and specific activity of S in the shoot were determined. Results In the first crop, the yield was significantly lower in the control (without added ES) and ES pastille treatments than in the other treatments. Sulphur uptake was highly correlated with the added sulphate rate. In the second crop, the yield and S uptake was highest for the S-fortified NP fertilizers. The contribution of ES to the S uptake was circa 20% in the first crop and 43% in the second crop for the S-fortified NP fertilisers, but was negligible for the ES pastilles. Modelling indicated an oxidation rate of 0.6−0.7 % per day for the S-fortified NP fertilisers and 0.03 % per day for the ES pastilles. Conclusions The contribution of ES pastilles to S uptake was negligible in both crops. In contrast, Sfortified NP fertilisers showed a significant contribution of ES and higher S availability than sulphate-only fertiliser in the second crop.

Slow-release boron fertilisers: co-granulation of boron sources with mono-ammonium phosphate (MAP)

The application of pure boron (B) fertilisers, independent of other macronutrients, is impractical due to the increased cost of dual handling and spreading. Bulk blending of B with other micronutrients is also an unattractive option as the relatively low rates of B required results in poor nutrient distribution in the field. Co-granulating B with other macronutrients such as mono-ammonium phosphate (MAP) may overcome these problems. Five B sources (boron phosphate (BPO4) synthesised at 500 and 800°C for 1 h, colemanite, ulexite and borax) were co-granulated with MAP to targeted B contents of 0.5, 1.0 and 2.0%. The co-granulated BPO4 had lower water solubility than co-granulated colemanite, ulexite and borax. Boron released from co-granulated borax, ulexite and colemanite was remarkably greater than co-granulated BPO4 products. Over a 4-week soil incubation period with weekly leaching of one pore volume of water, the cumulative B release from co-granulated ulexite, borax and colemanite was 97, 75 and 58%, respectively, but only 16 and 4% for the co-granulated BPO4 synthesised at 500 and 800°C, respectively. Co-granulated BPO4 products have potential as a high quality fertiliser to increase crop yield with slow B release.