How Sulfate Fertilizers Work

Sulfate Fertilizers

• Nitrogen fertilizers make soil more acidic over time, according to University of Guelph. Those growing acid-loving plants or who have alkaline soils find that their plants display unhealthy growth when the pH is outside of their range. A condition called chlorosis occurs when the soil is too alkaline. Chlorosis causes plant yellowing due to lack of chlorophyll. Plants that cannot adequately absorb the nutrients in soil outside of their preferred range suffer from nutritional deficiencies. Gardeners with alkaline soils benefit from using a sulfate fertilizer as long as their soil pH is 7.0 or below. Sulfate fertilizer is ineffective when the soil pH is above 7.0.

Types of Sulfate Fertilizers

• Numerous types of sulfate fertilizers are effective in lowering the soil's pH. For example, ammonia sulfate is converted into nitrate by the soil's bacteria. Ammonium polysulfide is applied into irrigation water, directly into the soil or by mixing with anhydrous ammonia or ammonia solutions, according to North Dakota State University. Because this type of sulfate fertilizer is not compatible with acidic fertilizers, gardeners cannot use it with a fertilizer high in salt.

Soil Testing

• Sulfate fertilizers should only be applied to alkaline soils to properly work. Test the soil in your yard before applying. Make several 3- to 4-inch holes in the yard and collect half a cup of soil from each. Mix the soil in a bucket. Remove any vegetation or debris. Send one cup of soil to your local cooperative extension office for an accurate assessment of your soil's pH and makeup. Wait a few weeks for results.

Other Factors

• Aluminum sulfate fertilizer should be applied at a higher rate than elemental sulfur, according to Iowa State University. Apply sulfate fertilizer at a rate five to six times higher than you would using elemental sulfur to lower the soil's pH. However, refrain from using more than 5 lbs. of aluminum or iron sulfate per 100 square feet. Using too much sulfate at one time will burn the plants. You may have to use several applications of sulfate fertilizers to achieve a range optimal for growing.