SULFHUR: THE FOURTH MACRONUTRIENT IN FERTILIZATION

In current fertilisation practices, sulphur is classified as a secondary macronutrient, but due to the increasingly widespread deficiency of this element, there are proposals to consider it the fourth macronutrient in plant fertilisation, after nitrogen (N), phosphorus (P), and potassium (K).

Sulphur deficiency in crops is becoming increasingly pronounced, and the application of this element is becoming necessary to improve crop yields.

In plant fertilisation, there is a law of the minimum, or Liebig’s Law, which states that crop yield is determined by the nutrient element that is present in the lowest quantity.

International organisations such as IPNI (International Plant Nutrition Institute) are studying the elemental sulphur requirements of our crops in order to take them into account and incorporate them into fertilisation programmes.

Requirements kg/t of grain or dry matter

Yields (t/ha)

S uptake (kg/ha)

Crop

Requirements (kg/t)

Yield (t/ha)

S uptake (kg/ha)

Alfalfa

2.7

10

27

Rapeseed

10.3

3

31

Sunflower

5.0

3

15

Maize

4.0

10

40

Soybean

7.0

4

28

Sorghum

3.7

10

37

Wheat

4.5

5

23

Source: Adapted from INPOFOS. Informaciones Agronómicas del Cono Sur, No. 4, December 1999.

The importance of sulphur in plant nutrition is determined by the functions performed by this element, both in the soil and in the plant, which include the following:

• Functions of sulphur in the soil: lowering pH, balancing electrical conductivity, increasing microbiota, and unlocking other macro- and micronutrients such as phosphorus.
• Functions of sulphur in the plant: it is necessary for the formation of essential amino acids such as cysteine and methionine; it is part of secondary metabolites involved in the smell and flavour of certain vegetables; it increases chlorophyll levels in leaves; and it also has a fungicidal and acaricidal function.