Sulfur Lowers Soil Alkalinity and Can Impact Plant Nutrients Like Iron

Q. I put sulfur in the ground around my yellow bells and the leaf edges which were browning cleared up. Why isn't sulfur mentioned more often?

When sulfur granules are spread on the top of dry soil it doesn't do much good. They don't dissolve and lower the soil alkalinity (measured as soil pH).

A. Sulfur is not usually mentioned much but it can be effective in soils for two reasons; it is a plant nutrient needed in large amounts by all plants and it can lower the alkalinity (soil pH) of soils under the right conditions. I dont mention it much because it needs wet soil and warm soil temperatures to work and can be a problem if the wrong kind of sulfur is used. Use sulfur, not a sulfate.

I dont want people applying a sulfate fertilizer thinking its going to work because it has sulfur in it. Ammonium sulfate is an acid type fertilizer but it is because of the ammonium in it, not the sulfur. This sulfur is reduced to its final state...sulfate, SO4...and cannot acidify the soil. Tricky thing about chemistry.

            Sulfur is needed by plants in large amounts. It is a plant nutrient. Most of our soils have enough sulfur in them from the parent rocks that adding it is not that important. If you are curious that your soil may not contain enough sulfur, send a sample to a soil testing laboratory, and find out. They need about 2 cups of soil to analyze it. Another option is to add sulfur to the soil (as you did) and look for plant improvement (which you also did).

A sulfur burner like this one burns sulfur and injects the gas from it into the irrigation system to lower the water pH (alkalinity).

            When pure sulfur dissolves in the soil it makes sulfuric acid. This acid helps to lower our soil alkalinity. This lowering of soil alkalinity is measured on the pH scale. This will not happen when using fertilizers that contain only sulfates. A lowering of alkalinity makes plant nutrients like iron, manganese, and zinc, needed in smaller amounts by plants, easily available.

 

Sulfur is available as water dispersible granules or in powder. This dissolved quicker than granules but still needs water to make it work.

            The problem with adding sulfur to soils is its granular size, the moisture needed to make sulfuric acid and warm soil temperatures. Mixing small or pulverized pure sulfur granules or sulfur powder into wet soil during the summer months has the best chance of reducing alkalinity in soil and getting good plant results quickly.