Ammonium Sulfate to Acidify Soil

About Soil pH

• Soils are commonly distinguished based on their soil pH. Soils with a pH above 7 are considered alkaline, whereas those with levels below 7 are acidic. Neutral soils have a pH of 7. Although soil alkalinity is desirable for some plants, it can cause nutrient deficiencies in others. Plants, like rhodondendron and blueberries, actually require very acidic soil conditions. Excessively high or low pH may result in nutrient deficiencies or toxicity, which can hinder plant growth and development.

Ammonium Sulfate and Acidity

• Ammonium sulfate is commonly used to lower the pH of soils. According to the Michigan State University Extension, it is particularly beneficial when used to amend soils with pH levels higher than 7. Ammonium sulfate is a byproduct of many industries, and is generally available in most home and garden centers. For maximum acidification, always incorporate ammonium sulfate into moist, aerated soil, since the chemical reaction will not take place without adequate soil contact.

Other Benefits

• Technically, ammonium sulfate is a fertilizer. This means that, in addition to acidifying soils, it also increases their nutrient levels. Nitrogen is one of the most important soil nutrients, and is often deficient in garden soils. Ammonium sulfate is composed of 21 percent nitrogen, and is also an excellent source of sulfur for deficient soils. This makes it an ideal soil amendment for soils that have excessively high pH levels in addition to low soil-nitrogen content.

Alternative Options

• Ammonium sulfate may not be appropriate for all soils. It should not be used to increase nitrogen levels if you need high soil pH, since it is an acidifying fertilizer that requires neutralization in order to avoid excessively low pH levels. It should also be avoided if your soil has normal or high nitrogen levels, since it will increase nitrogen content. Other acidifying soil amendments include aluminum sulfate, sulfur-coated urea and elemental sulfur.