The importance of sulphur

Most New Zealand soils are inherently deficient in sulphur (S). Managing this deficiency has been part of our agriculture since the first S deficiencies were discovered earlier last century. S is derived from soil parent materials and atmospheric deposition. As these amounts are generally low, fertiliser S must be applied to our pastures.

Plant S requirements
S is an important constituent of many enzymes in both plants and animals, with those enzymes being necessary for biochemical processes. It is required by plants for photosynthesis, as it is involved in chlorophyll production. It is also part of some proteins and vitamins. Deficiency of S can appear similar to nitrogen deficiency, with leaves becoming lighter and yellowish. Unlike nitrogen deficiency, it is generally first visible in the young leaves. It is often observed in winter, when significant rainfall has reduced the amount of sulphate in the soil, and paddocks become yellow or even orange-looking.

 Legumes (including clover) are more at risk of S deficiency than grasses, and crops have varying S requirements.

Elemental S or sulphate-S?

There are two forms of S fertiliser used in New Zealand - sulphate and elemental. Sulphate-containing fertilisers include Superten, Sulphurgain, Pasturezeal G2, Pasturemag and Sulphate of Ammonia. The sulphate-S is readily plant available.

Some fertilisers contain elemental S - examples are Pasturemag Peat, Pasturemag Pumice and the Sulphurgain range. Elemental S is more slowly available, as it needs to be converted to sulphate by soil bacteria before plants can use it. Elemental S is less prone to leaching.

Whether you are best to use elemental S or sulphate-S or both depends on a number of factors. Elemental S is most suited for use in the following situations:
  • On low ASC soils, such as peats, pumice and podzols, and some free-draining sedimentary soils
  • In high rainfall areas
  • When annual fertiliser applications are made in autumn
  • When fertiliser is applied less frequently than annually.

Sulphate-S is best used when you need the S to be available quickly, e.g. to support spring pasture growth, or in crop starter fertilisers.

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