Because it is a naturally occurring mineral, sulfur is approved as an organic soil amendment. However, it is not fast acting, it's effects are temporary and it takes a great deal to effect any significant change in soil pH.

Thank you for your advice

I see you live in Italy. Do you know the pH of the soil now? And where to you want it to be?

Do you know the nature of your soil? Is it mostly organic material, mostly clay, limestone? Seems to me there is a lot of limesone in Italy but I may be thinking of somewhere else. Are you trying to grow something that is not adapted to your area?

I'm not a big fan of using sulfur. It becomes sulfuric acid and kills the soil fungi as it changes the pH of the soil. Still, if you need to change the pH, sulfur is about the only organic approved material that will get you there quickly. General organic gardening with organic fertilizers usually changes the pH without doing anything else.

Applying large quantities of organic matter to soil will tend to raise the soils pH, not lower it. Sulfur is an acceptable way to lower your soils pH if that needs to be done, however, sufficient levels of organic matter in the soil can provide a buffer so plants will grow quite well even if the soils pH is not to their liking.

sufficient levels of organic matter in the soil can provide a buffer so plants will grow quite well even if the soils pH is not to their liking

On what do you base this statement?

Kimmsr,
Large amounts of organic matter will not raise the pH, it will stablize it! I don't know where you got that info. from, but it's inaccurate!

Ron
"The Garden Guy"
http://www.TheGardenGuy.org
Brand New Article & Garden Journal Entry 2/27

The pH of my soil that was 5.7 when we first moved here 35 plus years ago is today 7.2 with no lime of any kind, or any other mineral "fertilizer" added. The only thing added to this soil over those years was organic matter, compost, shredded leaves, etc. The only thing that could possibly have changed the soil pH here is that organic matter, since the rain and snow we get come from Milwaukee and the Chicago area where it picks up the sulfur dioxides that make it acidic. It has been established that compost, even when made from materials that react with a very acidic measure, will when finished composting be at or nearly at, neutral.
What I have seen is that soils, with inadequate levels of organic matter that do not drain well, are anaerobic, will tend to be acidic, while soils with adequate levels of organic matter in them, but also have sufficient levels of air, ie. aerobic soils, will tend to be more neutral.

As every gardening situation is different, it helps to make suggestions or recommendations that are based on science rather than empirical observations that may be influenced by issues or variables about which we have no first hand knowledge.

And the science is:

1) Organic matter does not raise soil pH, at least to any permanent degree (some OM, like certain animal manures, may be highly alkaline and provide a temporary bump until they are fully decomposed). OM tends to lower pH slightly, due to a) carbon dioxide from decomposing organic matter and root respiration dissolving in soil water to form a weak organic acid; and b) formation of strong organic and inorganic acids, such as nitric and sulfuric acid, from decaying organic matter. Once the decomposition process is pretty much complete, the resultant product is more or less neutral in pH.

2) Soils high in organic matter tend to resist changes in pH. This is because OM has a buffering capacity as a result of a high cation exchange capacity (CEC) that holds and binds elements - specifically hydrogen - that would ordinarily affect swings in pH. Thus, OM tends to be a stabilizing factor in soils rather a major activator in the adjusting of soil pH.

3) The addition of OM to a soil doesn't increase the range of plants that will grow in that soil except indirectly. And that's because of its physical properties that encourage the development of populations of beneficial soil organisms, its ability to improve soil texture and therefore its moisture holding capacities and its ability to bind and hold nutrients necessary for plant growth and health until they can be digested and made available by the soil organisms.

But the bottom line is that unless the soil pH is in the range that most plants prefer (slightly acidic to neutral), simply adding large quantities of OM is not going to supercede or override a pH that is greatly skewed in one direction or another. Or at least not in any kind of rapid fashion. If the pH is not to the
'plant's liking', it is not to the plant's liking and simply adding OM is not going to make "plants grow quite well" irrespective of pH.

If your soil is highly alkaline, adding recognized soil acidifiers is the only reliable way to make adjustments, which may very well be quite temporary and need to be repeated periodically. These would include elemental sulfur, peat moss, large quantities of not fully decomposed organic matter or ammonium based synthetic fertilizers. And of course, the last is not an option in an organic gardening context.

I'm more on gardengal's side of the explanation on this. She sort of said two different things but on the whole I am reading into it that OM will tend to neutralize both low and high pH soils and hold them toward neutral. I've been repeating that for years. I don't know where I first read it but the total accumulated experiences I've read on the forums seem to agree with it. For example (anecdotal, yes) my soil is white limestone with a pH in the 8s somewhere. There is no available iron in that soil until the pH drops below a certain level. My soil has enough organic matter in it, and I continually add organic fertilizer to it, that the pH drops enough to release the iron. When we get heavy rain, the pH rises back up and the iron becomes bound up - grass turns yellow. If I do nothing or if I fertilize with anything, it will not be until next spring until the pH has changed back enough that iron is available. Then I start to disagree with gardengal. I won't use sulfur because it is a common fungicide. I need all the fungi I can get. The only (other) material that makes a significant difference in in my yard is greensand. For some reason when I apply 40 pounds per 1,000 square feet of greensand, the grass will be dark green again in 3 weeks. I don't believe greensand is a recognized soil acidifier but it is the only thing that works for us in limestone.

This year I'm doing an experiment. For the past couple of years I bought greensand and never had a chance to put it out. This year I'm going to do it. If we get any rain before May I'll do it then. Otherwise I'll put it down on Memorial Day instead of corn meal fertilizer.

David,

Let us know how that turns out. I think greensand helps keep my lawn green despite growing on limestone rubbles. I have tens of thousand of earthworms that apparently turned the top 4-6 inches into nice crumbly black stuff and maybe made the iron from greensand more available to the root zone after digesting materials. Greensand is pretty cheap over here so I can just buy a lot and not go broke. I'm always shocked just how much more other places charges for greensand.

I am aware of what the Ag schools think about getting soil pH in the range that most plants grow best in, but gardeners in Ireland, Australia, New Zeland, England, Canada, Germany, The Netherlands, Malaysia, and a couple of other places I have probably forgotten, all have found the same thing happen with their soils, adding sufficient quantities of organic matter will change the soils pH. I am also aware that the initial tilling in of OM can cause a drop of soil pH, and that may well be another reason to not till your soil, very probably my applying the compost and shredded leaf mulches onto the soil and not in may be part of why the pH went up, and may also explain why in other soils the pH dropped toward neutral. Several soil scientists I have talked with are at a loss to explain because this is contrary to what they have been taught, which may well be wrong information, too.

dchall, I'd encourage you to study the sulfur cycle as it pertains to soils. Sulfur is a critical plant nutrient and goes through transformations to both organic and nonorganic compounds from mineralization and oxidation by soil microbes. It is very similar to the nitrogen cycle in that regards. It is just as necessary in maintaining a correctly diverse soil biology as all the other basic soil elements and is often lacking in heavily cropped soils. While it is often used as a topical fungicide, it does not necessarily follow that it is a uniformly acting fungicide when applied as as soil amendment, killing all the valuable soil fungi. In many cases, applications of elemental sulfur actually stimulate soil biology.

The interactions of basic soil elements and the soil microfauna are very complex and it is risky to make broad assumptions on how they interact just based on the principles that sulfur (or carbon as well, for that matter) has fungicidal properties, therefore it must kill off all beneficial soil-dwelling fungi as well. It is not that simple.

And sulfuric acid is only one of a number of compounds that are produced by applying elemental sulfur or sulfur fertilizers - more common is the oxidation of sulfur to sulfate or hydrogen sulfate. Sulfuric acid also gets rapidly converted to other compounds based on the presence of sulfur oxidizing microbes, soil mineral content, moisture, temperature and pH.

dchall, I'd encourage you to study the sulfur cycle as it pertains to soils.

Do you have any suggestions?

Again it's the dose that makes the poison. I'd like to know more.

I thought that bacteria were involved in turning sulfur into something that changes the soil pH.

Kimmsr: there may be any number of reasons why the soil scientists were at a loss to explain your situation, one could be you didn't provide them with enough information or incorrect information through no fault of your own. It is encumbent upon them to ask the right questions and helpful for you to provide accurate and precise information when there is no other.

I did some web searching using keywords 'sulfur' 'fungi' and similar. Some fungi are involved in conversion of sulfur, so I'm going to believe that moderate amounts of sulfur pellets are ok in soil.