MAY 2020
AGRICULTURE
Until the most recent amendment to the European regulations on fertilisers (Regulation (EU) 2019/1009), sulphur wasn’t considered a macronutrient, unlike phosphorous, nitrogen or potassium. The needs of this element were met by contamination or the contribution of sulphates from phytosanitary products which no longer exist, without the need for specific contributions.
Until the 1990’s, sulphur deficiencies in agricultural crops were extremely rare. This was mainly due to the fact that the availability of sulphur was guaranteed by the industrial SOx emissions generated by fuel combustion, by the well-known acid rain.
More restrictive environmental laws that came into effect, as well as the ban of certain sulphur rich agricultural chemicals and, namely, the increasing extraction of crops in increasingly intense agriculture have caused a sharp decrease in the availability of sulphur for plants in cultivated crops.
This phenomenon explains why sulphur deficiencies in crops are quite frequent today, even though they were rare 20 years ago. In this sense, a sulphur deficiency is more likely to occur under the following conditions:
Nowadays, agronomists from all over the world stress the need to consider the extra contribution of sulphur as a macronutrient, similar to NPK, given its essential importance for the optimum growth and development of crops.
Sulphur, along with nitrogen, is essential for the formation of vegetable proteins, through the amino acids cysteine and methionine, as well as for the synthesis of fatty acids and vitamins. Sulphur also has a significant impact on the quality, flavour and smell of crops, something that is increasingly important to the final consumer.
Sulphur is also involved in photosynthesis process, in the energy metabolism of the plant and in the production of carbohydrates.
Based on this information, the best way to provide sulphur in soil is in the form of elemental sulphur, as it is naturally oxidised by the soil’s microbiota until it is turned into sulphates which can be directly assimilated by the plant.
During this oxidisation process, the soil’s pH is lowered and this increases the availability of nutrients such as phosphorous, iron and copper, which remain blocked in soils with a basic pH.
On the other hand, the application of elemental sulphur contributes to the elimination of sodium retained in the soil change complex, balancing out its electrical conductivity.
In addition to this, sulphur is closely linked to nitrogen in a multitude of biological processes, as a component of the enzyme needed for nitrogen assimilation, and its deficiency severely affects the plants’ ability to metabolise it properly.
Using Liebig’s Law of the Minimum as a reference, the growth of plants is limited by the essential nutrient with the lowest concentration. Therefore, as Singh and Schwan's (2011) theory notes “for every kilogram of sulphur deficiency in the soil, fifteen kilograms of nitrogen will no longer be assimilated by the plants”.
Nitrogen application efficiency requires a proportional increase in sulphur fertilisation, otherwise this nitrogen will not be assimilated by the plant and costs, contamination and imbalance in the crop will be increased.
Finally, the enormous importance of sulphur as a natural product in organically certified crops shouldn’t be forgotten, as it is one of few viable alternatives for providing the plant with the nutrients it needs to promote the optimum development of its crops and, at the same time, increase its protection against plagues and diseases.
Watch this video to find out more information and get to know the benefits of sulphur as a macronutrient in agriculture.
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