Sulfur is considered as 4th important macronutrient 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 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 the younger leaves of the plants.
What Causes Sulfur Deficiency in Soil
Sulfur levels in the soil are influenced in different ways like
1. Availability of Sulfur
Sulfur is a natural component of the soil. However, there can be a deficiency due to either excess microbial activity or low availability.
2. Soil Plowing.
Plowing causes mixing up of soil, such that Sulfur moves into the deeper levels. The sulfates are absorbed by only the seminal roots present on the top layer of soil; Hence, if the sulfur is deficient in the upper layers, it decreases the availability of Sulfur near growing regions. So plowing soil should be done with care, avoiding going into deeper layers.
3. Organic matter content.
Organic matter present in the soil contains different elements, including sulfur. As per studies, Nitrogen to Sulfur exists in the ratio of 8:1. If the soil organic matter is high, then the sulfur level will also be high. Thus low organic matter can be a cause of low sulfur levels.
4. Microorganism availability
The micro-organisms in the soil convert the elemental sulfur into sulfates, which are easily absorbed by roots. However, in low sulfur levels, these microbes use up this sulfur, leading to 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. If the temperature is too high or too low, the microbial activity will be low, leading to sulfur deficiency.
6. Harvesting time
This is a general case where the sulfur is removed from the field with corn harvesting. During growth, crops stores some amount of sulfur in them. During harvest, this gets removed from the soil. Thus deficiency arises as those harvested crops taking away some of the sulfur doesn’t reach back to the soil.
Like other nutrients, the sulfur content in soil can be determined by examination of the soil profile.
But, this soil profile analysis is not preferred for sulfur. Because, for the analysis, the soil up to a depth of 25-30 centimeters is chosen. However, sulfur is available in the top layers of soil for utilization by plants.
Besides, there are also chances that the whole plot of land is not sulfur deficient and only some areas are deficient.
Hence, plant tissue examination is considered a preferred 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, farmers still add some sulfur while seeding. This is because sulfur lack of sulfur can stunt the growth of plants 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 until the seminal roots grow stronger and deeper for sulfur availability.
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.
- Organic matter removed 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 forms of sulfates are mentioned below
|Potassium magnesium sulfate
|Sulfate of micro-nutrients
|Ammonium phosphate sulfate
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
|Mono ammonium phosphate
|Sulfur coated fertilizers
Fertilizer having liquid sulfur.
This form of sulfur is available in liquid form.