Role of sulphur in plant nutrition
Until recently, nitrogen (N), phosphorus (P) and potassium (K) were considered as main nutrients for plants. However, studies of world leading experts in field of agrochemistry showed that sulphur (S) has to be included in this row. S - is vital nutrient for plants. S improves N and P assimilation by plants, increases draught and desease resistance. S - is the second after N protein forming element. S is a composite element of cysteine and methionine aminoacids, which are used in protein synthesis. Methionine is one of the irreplaceable aminoacids for humans and animals. S is a composite element of plant oils and vitamines. When sulphur deficiency plants stop protein synthesis. Thereby, nutrition value of a crop deminishes.
How much sulphur does plant need?
Sulphur demand varies among crops. This nutrient is basic for all plants, but especially it is required by oil crops, wheat, alfalfa, broccoli, cauliflower, celery, maize, sugar beet and sugar cane.
Sulphur in soil
As any other element sulphur exists in soil as available and not available for plants. Available sulphur is a component of readily soluble sulphates and is called as «mobile sulphur». Unavailable sulphur exists as a heavily soluble compounds (CaSO4) or as an elemental sulphur. Soils in Russia are divided into different groups depending on concentration of mobile sulphur:
- - soils with low sulphate fertility (< 6.00 mg/kg);
- - soils with moderate sulphate fertility (6.1 - 12.0 mg/kg);
- - soils with high sulphate fertility (> 12,1 mg/kg).
There is also another classification can be met in the literature (Ahmad et al., 1994), dividing soils according mobile sulphur content:
- - soils with insufficient mobile sulphur content (< 0.01 mg/kg);
- - soils with satisfactory mobile sulphur content (0.011 - 0.03 mg/kg);
- - soils with adequate mobile sulphur content (0.031 - 0.1);
- - soils with excessive mobile sulphure content (> 0.1 mg/kg).
However, the last classification can be used only for highly saline soils.