Soil Sulfur cheat cheat – a very short one

Soil sulfur is not a very well known element, but it is part of the macronutrients. Sulfur or S, is absorbed in the same amounts as phosphorus. Uptake of S by grasses is about 10 kg/ha,  leguminous crops 25-30 kg/ha and cabbage about 40-45 kg/ha.

The table below compares sulfur and phosphorus in the % dry material of various crops:

So why do plants need sulfur?

Plants take up sulfur in the form of S^2- and SO₂ through the leaves from the atmosfeer.

Sulfur is used in various functions in the plant such as:

• It is a component of egg whites and amino acids such as cysteine and methionine.
• It is a component of vitamin B1 and coenzyme A.
• It activates various poteolytic enzymes.
• It is an important part of the aroma in cabbage, turnips and onions.
• In conjunction with magnesium it helps with plant oil production.
• It helps with cold tolerance.
• It helps with nitrogen fixation in the soil
• It prevents nitrate accumulation by converting excess N to protein.

Deficiency symptoms of sulfur

The whole plant is light green.

Light chlorotic spots appear between the veins of leaves.

In some plants, a reddish colour may appear.

The chlorotic leaves do no dry out and don’t fall off as in the case of a fungus attack or nitrogen deficiency.

S is less mobile in plants than N.

High leaching under irrigation can cause S stress in plants without the grower noticing.  The first commercial identification was done in Malawi where S deficiency was misdiagnosed as Tea yellows. In South Africa some S deficiency occurs in Kwazulu Natal.

Conditions that are conducive to S deficiency are:

• High rainfall or high volume of irrigation.
• Coarse of rough soil texture throughout the soil profile promoting leaching.
• Warm climate that promotes biodegradation of organic material.
• The application of additional organic and non-organic material to the soil that results in wide C:S and/or N:S ratio.
• The use of fertilizer that does not contain sulfur such as double super phosphate.
• The use of crops with very high S uptake over a long time.

In intensive crop production S deficiencies are rare because most of the fertilizers and sprays already contain enough sulfur for the plant to grow optimally.

Featured image obtained from Pixabay. Image taken by Ildigo