Sulphur Fertilizer Management for Optimum Seed Yield and Quality of Canola in the Canadian Great Plains.
Sukhdev.S. Malhi, Agriculture and Agri-Food Canada, Hwy.6 South, Melfort, SK Canada S0E 1A0, Saskatchewan, SK 1240, Canada, Jeffrey Schoenau, Univ of Saskatchewan, 51 Campus Dr., Saskatoon, SK S7N5A8, Canada, and Cynthia Grant, Agriculture & AgriFood Canada, Grand Valley Road, Brandon, MB R7A5Y3, Canada.
In the Parkland region of the Canadian prairies, canola (Brassica napus L. or Brassica rapa L.) is an important cash crop. Canola has a high requirement for sulphur (S). However, many soils in this region are deficient or potentially deficient in plant-available S for optimum canola seed yield. Application of sulphate-S at about 15-30 kg S ha-1 is usually sufficient to prevent S deficiency in canola on most of the S-deficient soils. Application of sulphate-S to canola at seeding time gives the highest increase in yield and S uptake. Deficiencies of S in canola plants can be prevented and/or corrected and seed yield improved with the use of sulphate-S fertilizers in the growing season. Application of sulphate-S at bolting can substantially restore seed yield, while an application at early flowering can moderately correct S deficiency damage. Side-banding is the most effective way to apply sulphate-S fertilizers to produce maximum seed yield and to prevent any damage to canola seedlings from seed-row placement. In relatively moist areas, broadcast-incorporation method can produce seed yield similar to side-banding in most years. Elemental S fertilizers were not effective in increasing seed yield in the year of application, and were generally less effective than sulphate-S fertilizer even after multiyear annual applications, especially when applied in spring. Autumn applied elemental S was more effective than spring applied elemental S. Banding delayed availability of elemental S as compared to broadcast application. Use of granular elemental S products is not reliable for optimum seed yield of canola under Canadian prairie conditions on S-deficient soils, particularly in the initial year and with spring application or band placement. Elemental S fertilizers may have a role to maintain or build-up sulphate-S levels in soils marginally low in S where residual benefits are desirable, but management decisions should consider both immediate and long-term effects of S fertilizer on seed yield, seed quality and economics. The findings suggest the need of future research to increase dispersion and distribution of S particles from granules for faster oxidation of elemental S in soil, and develop elemental S fertilizer products/formulations that can be used on a commercial scale to prevent and/or correct S deficiency in the growing season to optimize seed yield and quality of canola. Research is also required to determine the long-term effects of balanced application of S with other nutrients on soil quality, accumulation and distribution of nitrate-N, sulphate-S and other nutrients in the soil profile, efficiency of nutrient, water and energy use, and crop diseases. More research should be conducted in relation to soil/plant tissue testing issues for optimum seed yield and quality of canola.