Soil Sulfur: How It Works

Soil sulfur could also be invisible to our eyes, however in our minds, sulfur is a yellow, powdery substance that we most affiliate with poor-smelling issues. Onions and garlic, as an example, each have a sure scent that may be attributed to sulfur. However sulfur not often will get the eye it ought to in soil and plant well being. Personally, I discover it to be essentially the most fascinating nutrient we as gardeners can examine. 

Sulfur itself is a crucial plant nutrient that has been written off as one thing poisonous to fret about within the soil science area. Whereas in earlier many years not worrying about sulfur could have been nice, issues have modified. This is because of extra efficacious environmental legal guidelines within the US and the world. The draw back: that, mixed with adjustments in fertilizer, led to extra widespread sulfur deficiencies. 

This text dives into the significance of sulfur in vegetation and soil. Diagnosing deficiencies, amending sulfur, and studying how sulfur cycles and its significance in vegetation will even be coated.  

Sulfur’s Function in Crops

Elemental sulfur. Supply: Nationwide Pesticide Data Heart

Sulfur is provided to the plant within the sulfate (SO42-) kind, taken in by the roots through soil answer. Generally sulfur dioxide (SO2) is taken in from the encircling air by leaf stomata. Nevertheless, the amount taken up in its gaseous kind is restricted. 

Sulfur has a crucial position in amino acid formation. Mixed with nitrogen, sulfur types many amino acid chains, that are the constructing blocks of proteins. Sulfur can be crucial within the technique of photosynthesis. Since photosynthesis is a vital course of the place a plant synthesizes its personal meals, guaranteeing enough sulfur is current is crucial. 

Sulfur is an important nutrient within the organic nitrogen fixation course of carried out by micro organism in relationship with vegetation and soil. That is why leguminous crops will want extra sulfur in comparison with different crops. Lastly, sulfur is a vital a part of the manufacturing of the pungent oils present in crops like garlic. 

Sulfur within the Soil

Just like its position in vegetation, proteins have a dominant position in relation to sulfur in micro and macro organisms present in soil. Since sulfate is just not a positively charged ion, it’s not concerned with cation change, the place totally different ions bond to 1 one other to create a functioning system of nutrient transmission to vegetation.

It’s as a substitute concerned in anion change, the place sure ions take away themselves for a similar objective. However some sulfur remains to be leached out of the soil profile on this course of. Outdoors of these items, the main position of sulfur is for decreasing soil pH

Soil pH

Sulfur-containing compounds are generally utilized in agriculture to decrease soil pH and thus make them extra acidic. It’s necessary to notice and perceive {that a} pH check measures the variety of free hydrogen ions in an answer. The distinction between every pH delineation is important, even when we’re speaking a few leap from a pH of 5 to six. As many people know, soil pH may be the distinction between a hospitable and inhospitable surroundings for a plant. 

The explanation sulfur acidifies soil is because of its reactions within the soil. Particularly, elemental sulfur creates a response that yields sulfate and free hydrogen atoms, which improve the soil acidity. Most sulfur-containing compounds have an effect on the soil pH. Elemental sulfur is essentially the most generally used to decrease pH, which gardeners add to soil within the type of compost or a sulfur-specific modification. 

An necessary factor to think about with elemental sulfur is that when it lowers pH, there’s a important organic impact on soil microbes. It’s not a chemical response, like liming the soil, the place carbonate works to extend soil pH. Which means that it might take a bit longer to decrease the pH than it will with lime, however sulfur will get the job achieved. 

Since this can be a organic response, making use of an elevated quantity of elemental sulfur is just not one of the best concept. Doing this might decrease pH to a degree the place aluminum toxicity is possible. I might suggest solely making use of elemental sulfur as directed on your soil texture sort and local weather. Sulfuric acid can be used to decrease soil pH extra quickly. Nevertheless, I don’t suggest this since it could go poorly for non-professionals. 

In the end, as with every thing involving soil and vegetation, utilizing a soil check can inform you the pH degree of your soil with certainty. In a traditional circumstance, the pH won’t be extremely acidic or fundamental on the pH scale. 

In some uncommon situations, iron sulfide could also be discovered on the soil floor. For those who discover this black substance in your soil, know that is of nice concern. More often than not, you gained’t discover iron sulfide in your backyard. However for those who not often see it, cowl up this acidic substance.   

Sulfur Necessities

As a result of it’s a macronutrient, vegetation want sulfur in increased portions than they’d micronutrients. After we take into consideration sulfur’s position in proteins and amino acids, we see the way it’s crucial for vegetation. As it’s with all vitamins, totally different species of vegetation require various quantities and combos. 

Sulfur percentages in dry matter can vary from .2-.5%. However figuring out what a plant wants based mostly on the proportion of a nutrient in its tissues is just not one of the simplest ways to measure how a lot sulfur so as to add to the soil. The easiest way to find out that is by measuring the ratio of nitrogen to sulfur. 

A 12:1 (N:S) or decrease ratio is usually current in leaf tissues. When the ratio of nitrogen turns into too nice, then the plant will begin to construct up sugars which are a magnet for various pests and ailments. Subsequently, the steadiness of sulfur to nitrogen is necessary for plant security.  

Recognizing a Sulfur Deficiency

Sulfur deficiencies are sometimes misdiagnosed as nitrogen deficiencies. It is because each assist a plant retain its inexperienced coloration. In both of those deficiencies, the principle symptom is yellowing, chlorotic leaves. Nevertheless, particulars are key when diagnosing points that happen with vegetation. 

Yellowing leaves, related to sulfur deficiencies, present up on newer leaves. Then again, nitrogen-deficient vegetation present this symptom on older leaves. It is because nitrogen is well translocated in vegetation and might fluidly transfer from one location to a different. Sulfur, then again, doesn’t transfer by plant tissues as simply.   

Sulfur deficiency in young leaves
Sulfur deficiency in younger leaves. Supply: Penn State

Sulfur Cycle

Let’s dive into the methods sulfur enters and exits the soil. It is very important perceive the sulfur cycle, and the way environmental rules which have benefited us have additionally impacted soils. 


Till just lately, sulfur deposition – a course of the place sulfur sediment within the air settles on the soil floor – was the first approach sulfur entered soils. As years went on and we burned coal and fossil fuels, they launched sulfur dioxide into the air. This compound was mixed with rainwater, and when it rained, the sulfur turned to sulfate within the soil. 

As establishments worldwide have moved to enact extra air air pollution measures, there was a big discount in sulfur dioxide launched to the environment. These rules have in the end benefited us as people, however they’ve restricted the methods sulfur beforehand entered the soil.


Many sulfate-containing minerals are weathered and damaged down by various pure processes. These minerals embody gypsum, epsomite, and a number of other others. The weathering course of takes time to interrupt down minerals, however when it’s full, sulfur is launched into the environment and turns into sulfate after interacting with oxygen. 

Then, within the technique of sulfur deposition we mentioned within the final part, sulfur settles on the earth and penetrates the bottom by irrigation water and rain.  

Natural Matter

Sulfur enters soils mostly by natural matter. That is the place 95% of sulfur absorption happens in vegetation. Sulfates are launched to plant roots as natural matter is damaged down by soil microbes. So long as soil microbes are energetic, this continuous and necessary technique of releasing sulfate happens. 

Natural matter content material varies relying on the kind of soils in query. Soils with higher clay content material have a higher capability to carry natural matter in comparison with sandy soils. 

Different Sources

Irrigation water offers a number of the sulfur provided to vegetation. That is one other approach sulfate is added to soils in a approach vegetation can entry it. Nevertheless, this isn’t a big approach it’s added to soils. Up to now, nitrogen fertilizer and different fertilizers contained sulfate as properly. 

Sadly, sulfur has taken a again seat, and ranges are a lot much less in business fertilizers, attributable to decreased ranges of atmospheric sulfur. In actuality, NPK ought to change to NPS due to sulfur’s influence on plant well being and its growing demand.  

Methods Sulfur Is Eliminated

Contemplating sulfur is an anion, or a negatively charged ion, it doesn’t cling to soil particles and tends to leach out of the soil profile. Whereas it doesn’t have the leaching potential that the anion nitrate does, it nonetheless leaches out at a excessive charge. However it doesn’t have the identical position in air pollution that phosphorus and nitrogen have. 

Probably the most important approach sulfur is faraway from soils is thru plant matter elimination. Eradicating plant matter and harvesting crops takes sulfur out of soils. Gardeners can keep away from this by leaving as a lot natural matter as attainable intact within the area. Utilizing a chop-and-drop technique with cowl crops is a method so as to add sulfur to soils. There are additionally sulfur-based soil modification merchandise that do the identical.  

A diagram of the soil sulfur cycle.
The sulfur cycle. Supply: Bantle

Sulfur Amendments 

There are such a lot of modification merchandise that enhance sulfur ranges in soil, there’s not sufficient time for them on this piece. Right here, I’ll solely record just a few of an important and customary ones.The simplest and most accessible of those merchandise is compost. Together with a well-rounded compost with a very good carbon-to-sulfur ratio can add sulfur whereas making it out there to your vegetation. 

Gypsum is one other frequent soil modification, out there in many various merchandise. I actually like gypsum as a soil modification, because it doesn’t have a powerful influence on pH however provides sulfur to plant roots. The one draw back is it takes some time to interrupt down in comparison with different related merchandise. 

Elemental sulfur, most frequently within the type of sulfuric acid, is an apparent alternative. Particularly in sandy soils that leach sulfur and have elevated pH, merchandise that include modification kill two birds with one stone, decreasing soil pH and offering sulfuric compounds to your vegetation. 

Epsom salt, the stuff you employ for private care, can work properly as a sulfur fertilizer. It’s recognized chemically as magnesium sulfate, and a seek for it’s positive to be fruitful. Nevertheless, keep in mind to check your soil earlier than you fill it with Epsom salt, as additions of extra may harm soils that have already got sufficient magnesium current. 

Steadily Requested Questions

Q: What does sulfur do to soil?

A: Typically, sulfur-containing compounds are used to scale back soil acidity. 

Q: How do you get sulfur in soil?

A: There are a number of methods to extend sulfur in soil. Growing the SOM (soil natural matter)  will increase sulfur. Offering natural matter additionally improves microbiome well being and will increase soil fertility and carbon sequestration. There are additionally loads of soil amendments that present soil with sulfur.

Q: What occurs if there may be an excessive amount of sulfur in soil?

A: An excessive amount of elemental sulfur causes acidity, which may leach poisonous metals into the encircling air and water. Aluminum toxicity happens when the soil pH falls under 4.5. Present liming brokers to enhance pH. Train endurance, as adjusting soil pH adjustments the chemistry of soil. 

Q: How a lot sulfur ought to I add to my soil?

A: The quantity of sulfur wanted is dependent upon a number of issues. Understanding your soil sort and doing a soil check is vital earlier than you add amendments. 

Q: Does my soil want sulfur?

A: Do a soil check to find out if sulfur must be added. In a container backyard, the necessity for sulfur is much less possible than it’s in a raised mattress or massive farm.   

Q: Is sulfur a very good fertilizer?

A: It’s a wonderful fertilizer. Offering a fertilizer that features sulfate is nice for the backyard. Gypsum, Epsom salt, and compost all add sulfur amongst different vitamins to soil. 

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