Sulphur (S) is considered to be the fourth major nutrient required by plants. It is often forgotten in the fertility program, yet most crops utilize as much S as phosphorus. Critical to growth, S plays a major role in the formation of proteins, enzymes, chlorophyll and effective nodulation.
Typically, S deficient crops are spindly, later maturing and the younger leaves are pale green to yellow in colour. In canola, the leaves may cup inwards and develop a reddish or pink colouration on the underside of the leaf.
SULPHUR DEFICIENT SOILS
Generally, S deficiencies occur on soils that are coarse textured (sandy), well drained and/or low in organic matter. Deficiencies are also noted on soils with a relatively long history of canola or alfalfa production in the rotation.
Depending on the crop and its growth stage, optimal nitrogen (N) to sulphur (N:S) ratios range between 7:1 and 15:1. To obtain the optimal plant N:S ratios, soil N:S ratios should be between 5:1 and 10:1, depending upon the crop grown. The ratio in the soil should always be lower than that required by the plant to ensure adequate N:S ratios in the plant.
A soil and plant tissue analysis will help identify the need for additional S and the rate required. When soil testing information is not available and the soil is thought to be marginally deficient in S, N and S should be added in a ratio of 7:1 for canola and 10:1 for wheat.
FORMS OF SULPHUR
Plants take up S in the sulphate form (SO4=). Ammonium sulphate supplies a readily available form of sulphate. The elemental form of S must be oxidized to the sulphate form before it is available to the crop. As a result, spring applied elemental S may not supply adequate sulphate to your crop during the growing period in which it is required.
General fertilizer recommendations