Ammonium sulfate is a highly effective, nitrogen-rich fertilizer used to promote vigorous vegetative growth. It is valued for its dual-nutrient composition, providing plants with a readily available source of nitrogen. Its properties make it a popular choice for growers seeking to quickly boost leaf and stem development. This compound also provides a secondary nutrient that impacts overall plant health and soil chemistry.
Chemical Identity and Composition
Ammonium sulfate is an inorganic salt with the chemical formula (NH4)2SO4. As a commercial fertilizer, it is commonly labeled with an N-P-K ratio of 21-0-0, indicating it contains 21% nitrogen. The nitrogen content is exclusively in the ammonium form, which is rapidly soluble in water and immediately available for plant uptake.
Beyond nitrogen, this compound contains a substantial amount of sulfur, typically around 24% by weight. This high sulfur content, delivered in the sulfate form, distinguishes it from many other nitrogen-only fertilizers. Manufacturers produce this crystalline solid by reacting heated ammonia gas with sulfuric acid. The resulting highly soluble crystals are suitable for direct application or for mixing into liquid fertilizer solutions.
Impact on Soil pH and Plant Nutrition
The compound’s primary mechanism of action revolves around the fate of the ammonium ion. Once applied, soil bacteria begin nitrification, converting the ammonium (NH4) into nitrate (NO3). This microbial transformation releases hydrogen ions (H+) into the soil solution, which causes the soil’s acidity to increase. This makes ammonium sulfate a highly effective acidifying fertilizer.
This acidifying effect is especially beneficial for managing alkaline or high-pH soils, as it improves the availability of micronutrients like iron, manganese, and zinc. The reduction in pH liberates these elements for absorption. The sulfur component is also a major nutritional benefit for plants, as it is a necessary building block for synthesizing proteins, amino acids, and enzymes. Furthermore, sulfur is required for the formation of chlorophyll.
Guidelines for Application
Applying ammonium sulfate requires an understanding of its potent acidifying effect and high nitrogen concentration. It is particularly well-suited for plants that thrive in acidic soil conditions, such as blueberries, rhododendrons, and azaleas. Crops with high sulfur requirements, including onions, garlic, and members of the cabbage family, also show a strong response to this fertilizer.
Soil testing is a prerequisite for application. This testing prevents over-application, which could excessively lower the soil pH or lead to nutrient imbalance. For turf or garden areas, a general guideline is to apply the granular product at a rate of approximately 0.5 pounds per 100 square feet, adjusted based on soil test results.
Application Timing and Watering
The fertilizer should be applied during the plant’s active growing season. After spreading the granules, thoroughly watering the area is important to dissolve the fertilizer and move the nutrients into the root zone. Immediate watering also minimizes the risk of leaf or root “burn” that can occur if the highly concentrated salt remains in direct contact with plant tissue.
Safety and Storage
Safe handling practices, such as wearing gloves and avoiding direct contact with the eyes and skin, should be followed. The product must be stored in a cool, dry place away from children and pets.