Sulphur fertilization: What has changed?
Cynthia Grant, AAFC Brandon Research Centre, Box 1000a, R.R.#3, Brandon, MB R7A 5Y3 E-mail: Cynthia.grant@agr.gc.ca

Sulphur is one of the major limiting nutrients for canola production, after nitrogen and phosphorus. Other crops have a lower sulphur requirement that, so are less likely than canola to respond to sulphur applications. In many parts of the world sulphur deficiencies are occurring more often than in the past because of depletion of soil organic matter, decreased atmospheric deposition resulting from clean air legislation, and use of purer fertilizer sources that are low in sulphur. Sulphur deficiencies can be affected by weather conditions. Extremely wet conditions may leach sulphur below the rooting zone, increasing the likelihood of sulphur deficiency. A range of sulphur fertilizer sources are sold, but plants can only use the sulphate form. Therefore, other sulphur sources must convert to sulphate before they can be used by the crop. Various modified elemental sulphur fertilizers have been formulated to hasten the oxidation to sulphate. The speed of conversion of elemental sulphur to sulphate depends on environmental conditions and the size and dispersion of the fertilizer particles, but is normally too slow to supply sufficient sulphur to a canola crop in the year of application. Sulphate fertilizers sources can be effective whether broadcast, in-soil banded or placed in the seed-row, so placement options are varied. However, soluble sulphur fertilizers can be damaging to germinating seedlings if placed too near the seed. The damaging effects of different seed-placed nitrogen, phosphate and sulphur fertilizers can be cumulative, so care must be taken to avoid placing too much fertilizer in the seed-row and the interactive effects of the various fertilizer sources should be considered.