4 ways to lower and maintain soil pH
Why is our PH is so high despite the level of sulfur?
I am not a chemist however I have now been dealing with issues (native soil pH 8.4) for 2 seasons in the Mojave Desert. I have spent a lot of time trying to figure out the chemistry involved and it is quite complex since micro-organisms, irrigation water, and soil composition all factor into the final equation.
As you may be aware, elemental sulfur only modifies the pH of soil after it is oxidized by soil bacteria and converted to sulfuric acid. Secondly, the sulfur eating bacteria will only flourish if the right environmental conditions are met; Moisture, heat, and oxygen. If no oxygen is present, elemental sulfur may be digested by anaerobic bacteria producing toxic hydrogen sulfide gas. Its my understanding that elemental sulfur is unavailable to the plants as a nutrient and must be in a different form in order to be utilized by the plant. Conversely there may be forms of sulfur that cannot be utilized by soil bacteria.
If so, what can we do besides adding more sulfur to even out the PH a bit?
I don't believe that there is any likely hood that you will damage plants from excess sulfur fertilization. Its virtually unheard of.
I have used four different products to lower my soil pH.
The most commonly available elemental sulfur preparations with 10% bentonite clay, break down very slowly in the soil, may take years to be effective, and if the right conditions are not present, could be useless or detrimental. If properly utilized, elemental sulfur can be a powerful tool in maintaining a lowered pH over a long period of time but provides no immediate benefit.
Fertilizing with ammonium sulfate will lower pH over time since sulfuric acid is formed during the break down of this chemical. This will not meet your immediate concerns.
Another product that is commonly used is aluminum sulfate. Flower growers use it to lower soil pH around hydrangeas thereby turning them blue. You can think of this product as acid in powder form. When it contacts water it forms sulfuric acid (which you want), and aluminum (which you don't want). Excessive use of this product may cause aluminum toxicity.
The fourth, most effective, immediate way to lower soil pH is to add liquid sulfuric acid . The good part is that you will instantly change the pH of your soil.. The bad part is that this stuff is highly corrosive so you must take safety precautions very seriously. Contact will cause severe burns to your body. Read precautions on the bottle carefully.
I apply it prior to planting. In high concentrations it will sterilize the growing medium and kill vegetation that it comes in contact with. First, I dilute the product before application then later I thoroughly drench my planting beds with tap water to disperse the acid throughout my beds. After application you may consider tilling the soil and adding compost to recolonize the soil food web. I have planted within 24 hours of application with good results.
Concentrated sulfuric acid is found in the janitorial section of many national home improvement stores such as Lowe's and marketed as sulfuric acid "Drain Opener". It will be in a plastic bottle with a sealed clear plastic bag fully enclosing the bottle.
So there you have it, four very different products for acidifying your soil, each with its own unique pros and cons. And remember, its best to modify the soil pH in increments rechecking your results repeatedly, rather than over-correcting.
I welcome any corrections or discussion since I am always endeavoring to increase my understanding of soil chemistry and the soil food web.