ARCHIVE: Fertiliser Manual (RB209)

Sulphur

(Section 8 contains additional information for grassland)

Sulphur is an important plant nutrient and plants need about the same amount of sulphur as of phosphorus. Historically, the crop’s requirement for sulphur has been met from fertilisers that contain sulphur (e.g., ammonium sulphate) or contained sulphur as a co-product (e.g., calcium sulphate is a co-product in single superphosphate but not in triple superphosphate or ammonium phosphates). Many of these sources containing sulphur are no longer widely used.

Additionally, in the past, large amounts of sulphur were released into the atmosphere from industrial processes and this sulphur was deposited on land. However, atmospheric deposition has declined greatly in recent years and levels in 2007 were only about 10% of those in 1980. Consequently, crops should be monitored for signs of sulphur deficiency.

The map shows sulphur deposition in England, Wales and Northern Ireland in 2006.

The occurrence of sulphur deficiency

There is an increasing risk of sulphur deficiency in England and Wales in a wide range of crops including cereals, oilseed rape, brassica vegetables, peas and grass. Oilseed rape and grass grown for silage are particularly sensitive to sulphur deficiency. As atmospheric deposition of sulphur continues to decline, it is likely that the risk of deficiency will affect an increasingly wide range of crops grown on many different soil types.

Currently the best guide for assessing the risk of sulphur deficiency is soil type and field location. Sandy, shallow or medium textured soils that contain little organic matter are most susceptible to sulphur deficiency. Sulphate-S (SO42-, the form of sulphur taken up by crops) is not retained in soil because it is soluble in water and is easily leached. Deep silty or clay soils, or fields that have received regular applications of organic manure and organic soils are less likely to show deficiency. Sulphur is retained in soil in organic matter and can become available to plants, like nitrogen, when organic matter is decomposed by soil microbes.

Diagnostic methods

Sulphur deficiency causes paling of young leaves and crop stunting that can easily be confused with nitrogen deficiency (which usually affects older leaves first). In oilseed rape, middle and upper leaves can show interveinal yellowing, and flower petals are unusually pale. Leaf analysis is a useful guide to diagnosing deficiency in cereals, oilseed rape and grass but interpretative criteria have not yet been established for other crops. Although analytical results may be available too late to correct deficiency in the current crop, they can be useful for decisions on sulphur use for future crops. The procedures for plant sampling and interpretation of analytical results are given with each crop recommendation table. The malate/sulphate ratio test, developed for oilseed rape and cereals, can give a prediction of likely deficiency.

Soil analysis for sulphate-S to 90 cm depth can help identify severely deficient soils but in other situations is not as reliable a guide as leaf analysis.

Sulphur recommendations are given as kg SO3/ha not kg S/ha. Conversion tables are given in Appendix 8.

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