Effects of Seed-Placed Sulfur and Phosphorus on Wheat, Canola and Pea Yields, Sulfur Uptake and Recovery in Saskatchewan Soils.

Sulfur (S) fertilizers are typically recommended for canola crops and occasionally recommended for cereal and pulse crops on the Canadian prairies. Sulfur sources include soluble ammonium sulfate (AS) and potassium sulfate (PS); slightly soluble calcium sulfate (gypsum); and reduced forms including elemental sulfur (ES) and liquid ammonium thiosulfate (ATS) that undergo oxidation in the soil. Our objective was to compare S fertilizer forms for their effects on yield and S uptake alone, and in combination with monoammonium phosphate (MAP) fertilizer, in three prairie soils. Crops evaluated were wheat (Triticum aestivum.), canola (Brassica napus) and yellow pea (Pisum sativum) in a Brown and Gray-Black Chernozem and a Gray Luvisol soil in Saskatchewan, Canada. The five S fertilizer forms, with and without the addition of MAP fertilizer, were applied in the seed row at rates of 20 kg S ha-1 and 20 kg P2O5 ha-1 . All soils had moderate levels of sulfate sulfur present in the soil profile at the time of seeding, and were considered marginally deficient in plant available sulfate. Sulfur deficiency is generally more frequent in the Gray Luvisol soils due to lower S mineralization capacity and lack of reserves of subsoil sulfate. In the Gray Luvisol soil, sulfate forms resulted in higher canola yield than elemental S or ATS while little response was observed from any of the S forms for the Gray-Black Chernozem and the Brown Chernozem. Ammonium thiosulfate and gypsum were most effective S sources for pea. The ATS plus MAP was most effective in increasing wheat yield at the Brown and Gray Luvisol sites. Subsoil reserves of sulfate at the Brown Chernozem site and high organic matter and good mineralization capacity in the Gray-Black Chernozem soil explains the limited plant response to S fertilization.