There are four main sources of sulphur for plants:
After the industrialization of Europe and other Western countries, sulphur emissions increased until the harmful effects of sulphur dioxide emissions were recognized such as the effect of acid rain upon the surrounding environment, and also the effects on human health. Legislation has since been introduced to regulate the use of sulphur and to reduce sulphur emissions, and generally emissions in Western countries have declined considerably, but as a result however, many crops have been left with a sulphur deficiency. Due to more stringent emission controls, deposition of sulphur from the atmosphere dropped from more than 100 kg SO3/ha to as little as 25 kg SO3/ha in some areas. Leaching in arable soils has equally resulted in decreasing sulphur levels.
This, coupled with the earlier change in Europe to low sulphur fertilisers has meant that crop responses to sulphur-containing fertilisers are now becoming common. There is evidence from the UK that the reduction in sulphur emissions is running almost 10 years ahead of schedule and that the incidence of sulphur deficiency is increasing. Sulphur deficiency varies amongst the European countries, and at this point in time Eastern Europe in particular is less likely to respond to sulphur-containing fertilisers. However, with re-structuring of heavy industry in eastern states and the need to abide by EU environmental rules in the future, it is likely the same developments will take place throughout Europe. In conclusion, the need for sulphur fertilisers for optimum crop yields, for optimum use of nitrogen and for crop quality is increasing rapidly and will become more widespread in the near future.
The amount of sulphur released by breakdown of soil organic matter has been thought to be as little as 10-30 kg SO3/ha. Additional research is underway concerning an apparent inconsistency in the relatively large amount of available sulphur detected by deep soil sampling and the widespread incidence of crop responses to sulphur.
The forms of sulphur in soil organic matter are both varied and complex. It remains unclear how different fractions of organic sulphur are interrelated in the turnover processes. Microbial biomass-sulphur is probably the most active component of soil organic sulphur. Methods which fractionate soil organic sulphur into different pools according to their biological and biochemical liability need to be developed, and these may be more informative. Data on soil sulphur turnover from field studies, which are essential for developing and validating models, are scarce and scattered.
Sulphur content in organic fertilizers varies. Cow and pig manure usually contain around 1.8 kg SO3/t, cow and pig liquid manure contains around 0.8 kg SO3/m3, compost - around 3.8 kg SO3/t and poultry manure - about 8.3 kg SO3/t. During storage the content of available sulphur does not exceed 5%. Application of 30 t/ha of organic fertilizers can forward only 1.5 kg/ha of available sulphur.
Sulphur content fertilizers can be devided into three groups:
- - fertilizers that contain sulphur in sulphate form;
- - fertilizers that contain elemental sulphur;
- - liquid sulphur content fertilizers.
Among fertilizers of first group are: nitrate sulphates, ammonium sulphate, simple super phosphate, potassium sulphate, magnium sulphate and calcium sulphate. These fertilizers have an advantage that sulphur is in the sulphate form.
Fertilizers containing elemental sulphur belong to the second group. These are more concentrated. However, elemental sulphur has to be oxidized to sulphate form to become available for plant assimilation.
To a third group of fertilizers urea, covered with sulphur (SCU), and ammonium thiosulphate (ATS) solution are related.
|Sources of sulphate SO42-|
|Magnium sulphate (Epsom)||18|
|Magnium sulphate (Kiesirite)||22|
|Sources of elemental sulphur|
|Triple superphosphate granulated with sulphur||18|