Sulfur is considered as 4th important macro nutrient after Nitrogen, Phosphorous and Potassium.
The Sulfur deficiency is caused due to less availability of sulfates in soil. In soil, there will be approximately 1/8 Sulfur to nitrogen ratio. If an organic matter is present in the soil, it has about 80% nitrogen and 10% Sulfur. Just as the nitrogen is absorbed into plants in the form of nitrates, the Sulfur is absorbed in the form of sulfates.
But compared to nitrates, sulfates have low mobility from older regions to younger regions in the plants;
Therefore, the chances of sulfur deficiency are observed in younger leaves of the plants.
Factors that affect the Sulfur levels in the soil are
1. Availability of Sulfur
In the soil, if the amount of Sulfur present is not enough for plants to grow well, then the soil is Sulfur deficient. This deficiency can be due to microbial activity or low availability.
2. Soil Plowing.
Plowing causes mixing up of soil, which can result in Sulfur moving to the deeper levels. The sulfates are absorbed by only the seminal roots that are present on the top layer of soil; if the sulfur is deficient in the upper layers, it leads to a decrease in the availability of Sulfur near growing regions.
3. Organic matter content.
Organic matter present in the contains various elements, including sulfur. As per studies, there exists 8:1 Nitrogen to Sulfur ratio. If the soil organic matter is high, then the sulfur level in the soil is high.
4. Microorganism availability
The micro-organisms in the soil convert the elemental sulfur into sulfates, which are easily absorbed by roots. However, in the case of low sulfur levels, these microbes use up this sulfur leading further sulfur deficiency.
The temperature in the soil affects microbial activity. Since microbes convert sulfur to sulfates, the optimum temperature is required for the maximal activity of microorganisms.
6. Harvesting time
This is a general case where the removal of sulfur takes place routinely with corn during harvesting, as harvesting season starts crop stores some amount of sulfur and while harvesting it gets removed form soil as results deficiency symptoms arise as those harvested crops take away some of the sulfur which doesn’t reach back to the soil.
Like other nutrients, the sulfur content in soil can also be determined by the examination of the soil profile.
However, for sulfur, soil profile analysis is not preferred. For analysis, soil up to a depth of 25-30 centimeters is chosen. But sulfur is available in the top layers for utilization by plant.
Also, there are chances that whole plot of land is not sulfur deficient but only some areas or slots are deficient. Hence, plant tissue examination is considered as a prominent method for the sulfur profile.
In tissue examination, if the results are showing more than 50 indexes, then the sulfur content is said to be high, between 25-50 it is moderate, below 25-10 it’s low and if it is less than 10, it’s very low.
But when the index is moderate or high, still growers add some sulfur while seeding because sulfur is a stunting element that can stunt the growth of plant or roots. It’s a key element for the formation and development of seminal roots to the deeper region for proper absorption and intake of nutrients.
When adding sulfur to low soils, farmers wait till the seminal roots grow stronger and the deeper for the availability of sulfur.
If that’s not happening and younger plants show deficiency symptoms, then the external addition of sulfur is performed.
Adding sulfur should be performed in a specific ratio with nitrogen. For every 8 ratios of nitrogen, 1 ratio of sulfur must be executed for proper soil mixture.
Methods to conserve sulfur in the soil.
- Removed organic matter during harvesting should be added back to the soil.
- Plowing should be minimized to 1 or 2 times per season as mixing up can shift sulfur to deeper layers.
- Proper examination of the soil profile and deficiency symptoms should be performed regularly.
sulfur fertilizers are grouped under 4 categories.
- Fertilizer containing sulfate
- Fertilizer containing elemental sulfur.
- Fertilizer containing both sulfate and elemental sulfur
- Fertilizer having liquid sulfur
Fertilizers containing sulfate.
There are various combinations for the supply of sulfur. But this is considered to be the most prominent way as it has an ionic form of sulfate. This is readily absorbed by the plant from the soil. Some form of sulfates are mentioned below
|Fertilizer name||Sulfate percentage|
|Potassium magnesium sulfate||22%|
|Sulfate of micro-nutrients||13%-21%|
|Ammonium phosphate sulfate||14.4%|
Fertilizer containing elemental sulfur.
This form of sulfur is mainly used to reclaim soil having greater than 15% of sodium CEC (anion exchange capacity) and mainly used for lowering the soil pH. Some forms of elemental sulfur are
|Fertilizer name||Sulfur %|
|Mono ammonium phosphate|
|Sulfur coated fertilizers||14%-20%|
Fertilizer having liquid sulfur.
This form of sulfur is available in liquid form.
|Fertilizer name||Sulfur %|