Sulfur in soil and in the plant


Sulfate behaves like nitrate in the soil

In the plant nitrogen and sulfur are both essential building blocks for proteins. Sulfur deficiency will severely reduce the efficient use of nitrogen and limit protein synthesis. Since industrialization a lot of soil sulfur came from sulfur dioxide in air pollution (from burning fossil fuels). Declining emissions are reducing this source of atmospheric sulfur making balanced fertilizer application even more important.

Sulfur can only be taken up by plants from the soil solution as sulfate. As with readily-available nitrate, it can be liable to loss through leaching. Spring application of sulfate fertilizer is therefore recommended so that the plant can take it up during the period of active growth, as with nitrate. Sulfur is required together with nitrogen for the formation of proteins and uptake timings are similar.

The Sulphur Cycle


infoElemental sulfur

While sulfate fertilizer is immediately available to the crop, applications of elemental sulf ur must be converted to sulfate by bacterial activity in the soil before it becomes available. The time taken for this oxidation is unpredictable and may take many months, so the sulfate required by the crop may not be available when needed.

Protein synthesis

Sulfur is required for many growth functions in plants – like nitrogen it is principally an essential constituent of protein. There is therefore a close relationship between the quantities of nitrogen and sulfur in crops, with most taking up about 1kg of sulfur (2.5kg SO3) for every 12kg of nitrogen.

SO3 UPTAKES BY WHEAT, POTATO AND CABBAGE DURING THE GROWING SEASON
SO3 UPTAKES BY WHEAT, POTATO AND CABBAGE DURING THE GROWING SEASON

Brassica crops, such as oilseed rape, cabbage and kale, require much more sulfate. They need extra sulfur for the production of glucosinolates, which are used within the plants as a defense mechanism.

Once taken up, unlike nitrogen, sulfur does not move against the transpiration stream and cannot be taken from older leaves, for example, to support new growth. So a sufficient and continuous supply is needed in the soil to satisfy all the needs of the growing crop.

Signs of deficiency include the yellowing of young leaves or new growth. By contrast, yellowing from nitrogen deficiency affects the older leaves first.

Sulfur-deficient oilseed rape can also have purpling and upward cupping of young leaves, delayed and prolonged flowering, pale-colored flowers, and fewer, smaller pods.

The risk of sulfur deficiency can increase in countries where levels of atmospheric sulfur - from air pollution through fossil fuel combustion - decline. The US and EU have seen sulfur dioxide emissions drop rapidly.

As recently as 2001, soils in most of Indiana received more than 13 pounds of S per acre from the atmosphere. Extensive areas of southern Indiana received more than 18 pounds of S per acre. In recent data from 2015, S deposition was less than 10 pounds per acre throughout Indiana.

REDUCED SULFUR DEPOSITED ON LAND IN 2015 COMPARED TO 2001.

Red colors indicate high deposition and blue low deposition.
Source: http://nadp.isws.illinois.edu (accessed June 2017)