Certified Crop Advisor Practice Exam

Which of the following sources of phosphorus is a liquid?

1. Monoammonium phosphate

2. Ammonium polyphosphate

3. Rock phosphate

4. Superphosphate

The correct answer is: Ammonium polyphosphate

Ammonium polyphosphate is a liquid source of phosphorus due to its formulation and manufacturing process. This phosphate fertilizer consists of a combination of ammonium and polyphosphate, allowing it to be produced in a liquid form. The liquid state is advantageous for certain application methods, such as fertigation, where nutrients are delivered directly through irrigation systems. The other options, while they are valuable sources of phosphorus, do not come in liquid form. Monoammonium phosphate is typically available as a solid granular fertilizer, and rock phosphate is naturally occurring and is usually mined as a solid. Superphosphate is another solid fertilizer that results from the reaction of rock phosphate with sulfuric acid, producing a solid product rather than a liquid. Thus, ammonium polyphosphate stands out as the only liquid phosphorus source among the provided choices.