According to the Potash Development Association (PDA), sulphur is an essential nutrient for all plants and animals.
But, as its behaviour in the soil is very similar to that of nitrogen, high rainfall can lead to leaching.
This could lead to sulphur deficiencies despite attempts to avoid this.
Sulphur is known to be important for yield and crop quality.
However there is strengthening evidence to suggest that sulphur has an important relationship with a large number of other nutrients.
So, ensuring an adequate supply through the growing season could be key to ensuring these other nutrients are taken up efficiently also.
Sulphur
Sulphur is an essential nutrient for all plants and animals, with some crops more vulnerable to deficiency than others.
Historically, sulphur was deposited on land from the atmosphere in more than adequate quantities for optimal growth and development throughout many parts of the UK and Ireland.
However, as the burning of high sulphur coal in power stations was switched to imported natural gas, aerial deposition declined dramatically.
This continued when emissions regulations forced flue gas desulphurisation units to be fitted, and now very little of the element is deposited on our fields.
As recently as 30 years ago, there was as much as 130kg/ha/year of sulphur was deposited.
However, it is now estimated that this figure could be as low as 1-3kg/ha over the year.
As a result of this reduction, soils are now showing critical signs of sulphur deficiency and applications of the element to crops has become an essential part of nutrient management planning on tillage farms.
Nutrition planning
Sulphur in the soil behaves in a similar way to nitrogen. It becomes plant-available from the breakdown of organic matter, and to some extent from soil minerals.
Soils which are organic or heavy textured are more able to supply sulphur than light and inorganic soils.
Plants take up sulphur in the form of the sulphate anion. These predominate in the soil solution, which means they are at risk of leaching, depending on the soil texture and rainfall – again just like nitrate.
This risk must be taken into account by growers when nutrient planning.
Both the organic processes leading to the availability of sulphur for plants, and its leaching potential cause levels of the element in soil solutions to vary by month and by year.
Sulphur is essential for protein synthesis, to maintain the balance of amino and sulphur-containing compounds.
Due to the central role of both sulphur and nitrogen in the synthesis of proteins, the supplies of these nutrients in plants are highly inter-related and a shortage in the availability of sulphur will reduce the efficiency of nitrogen use.
As well as protein synthesis, sulphur is essential for plants to form enzymes, vitamins, and chlorophyll. In legumes, it is crucial in nodule development and efficient nitrogen fixation and is critical for determining the nutritional quality of foods.
Up to now, it has been usual practice to apply a readily soluble source of sulphate in the early spring in the expectation that it will provide the chemical element throughout the growing season.
However, it is now believed that sulphur should be applied throughout the growing season to match both available nitrogen for these and possible leaching losses.
