Certified Crop Advisor Practice Exam

Which material is known to reduce phosphorus availability in manures?

1. Gypsum

2. Alum

3. Lime

4. Compost

The correct answer is: Alum

Alum, or aluminum sulfate, is known to reduce phosphorus availability in manures due to its chemical properties. When added to manure, alum reacts with phosphorus to form aluminum phosphate, which is less soluble and thus less available for plant uptake. This process not only decreases the phosphorus content that may be released into the environment when the manure is applied to fields but also helps prevent potential water quality issues associated with phosphorus runoff. In contrast, gypsum primarily provides calcium and sulfur without significantly affecting phosphorus availability. Lime is mainly used to raise soil pH and does not have a substantial effect on phosphorus. Compost can improve nutrient availability in soils but does not specifically reduce phosphorus availability. Hence, alum is the effective choice for addressing phosphorus management in manure.