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  • Sulphur (S)
    1632.064
    S
  • Ionic form
  • Anion/Cation
    SO42-
  • Leaf
  • Origine: Volcanic
  • >40mm around the root

Sulphur

(S)

Alongside the primary nutrients (N, P and K), sulphur is the most important secondary nutrient (Mg, Ca and S). However, sulphur fertilization is a relatively new topic. Following a sharp reduction in atmospheric fallout and other sources of supply (through plant protection products or animal manure), the application of sulphur through mineral fertilization has become crucial. Soil microbial activity (mineralisation) releases sulphur in available form. Mineralisation depends on soil temperature. Like nitrogen, it is mobile and sensitive to the risk of leaching in its plant available form (sulphate, SO42-) due to winter rainfall. Therefore, the first application of sulphur should occur after wintertime when vegetation restarts, in a balanced ratio together with nitrogen.
S
Plant
Plant
Soil
Soil
Crops
Crops
Origin
Origin
Keys
Keys
Importance for plant life
Sulphur is indispensable for many essential amino acids, particularly cysteine and methionine. Plants need it early on in chlorophyll for photosynthesis and protein formation. Sulphur deficiency leads to the discoloration or yellow staining of cereal crops at the end of winter.
Absorption mechanisms
Plants absorb sulphur through their roots in the form of sulphate SO42- Sulphur is mobile in the soil solution and its uptake by the plant is semi-passive and semi-active.  

INTERACTIONS AND SPECIAL FEATURES
Only the sulphate form can be taken up by plants. The elemental form needs to be oxidised to facilitate uptake. The thiosulphate form is an intermediate form.
As soon as the temperature is high enough (>12°C), organic matter, in which most of the soil-sulphur is stored, is mineralised and supplies the crops in the summer months.
Cycle diagram

1. The recycling of nutrients contained in organic matter such as livestock effluent, crop residues and other organic by- products of human activities, is an important resource for fertilization.

2. Fertilizer manufacturing can lead to formulations containing sulphur in sulphate form.

3. Some plant protection products add sulphate or elemental sulphur, which oxidises into sulphate in the soil.

4. Sulphur emissions from factories and vehicle exhaust declined significantly, leading to a sharp drop in atmospheric fallout in the past 40 years.

5. The incorporation into microbial or plant biomass transforms mineral sulphate into organic sulphur. The activity of soil bacteria is mainly stimulated by the presence of ammonia, nitrogen and sulphate. Organic sulphur must be mineralised to be absorbed by plants. Mineralization of organic matter  in the soil liberates sulphate.

6. In aerobic conditions, the ultimate form of mineral sulphur is sulphate, but in anaerobic conditions, sulphate may be reduced to sulphide and hydrogen sulphide (H2S).

7. Sulphate leaching occurs mainly in winter, when surplus water carries sulphate out of the reach of roots.

8. Plants only take up sulphur through the roots in sulphate form.

9. Leaf absorption in the form of elemental sulphur (S) vapour is possible, but limited.

10. Sulphur is exported via the harvest as food and fodder.

Sensitivity table

Sensitivity meter:
  • Very

  • Fairly

  • Moderately

S SO₃
Cabbage
Winter Rapeseed
Spring Barley
Winter Barley
Winter Wheat
Potatoes
Sugar Beet
Sunflower
Apple
Carrot
Cherries
Cucumber
Grape Vine
Lettuce
Pear
Grain Maize
Silage Maize
Strawberry
Tomato
Fiber Flax

Sensibility table & Symptomes

Sulphur is not very mobile in the plant. Deficiency generally appears in young leaves, leading to a yellowing of the leaf. It can be easily mistaken for nitrogen deficiency.

Excess & Needs

Excess sulphur can acidify the soil, which is positive in calcareous soils. Gypsum (calcium sulphate) does not interfere with the pH.

Sulphur is of natural origin, either in the elemental form from volcanic rock or from the purification of gas or petroleum. Atmospheric fallout of sulphur in the form of acid rain, which was significant in the 20th century, has been reduced by more than 80% in most countries.
Soil content
Sulphur measured via soil analyses (such as the Scott method) is closely linked to the organic matter content of the soil. Crop, climate and soil texture are the most relevant parameters to consider. 
Organic matter content
Most sulphur present in soil is in organic form; as a result, the higher the organic matter content of the soil, the more sulphur is provided from mineralisation during the growth period. Regular applications of organic fertilizers can greatly reduce the risk of deficiency considering though that only the sulphate form is directly available and mineralization depends on appropriate soil temperature.
Texture
Like nitrogen, sulphur is highly mobile in the soil solution, with a high leaching risk if rainfall is abundant in the autumn and winter. Losses are greater in filtering textures like sandy soils.
Climate
The frequencies and quantities of water largely determine the leaching of sulphur. The heavier the winter rainfall, the more sulphur is leached.