Question

The water soluble P (as % $\text{P}_2\text{O}_5$) in diammonium phosphate (DAP) is

• A. 45
• B. 45
• C. 40
• D. 40

Hint:

Remember the nutrient profile of DAP:
- Total \( \text{N} = 18\% \)
- Total \( \text{P}_2\text{O}_5 = 46\% \)
- Water-soluble \( \text{P}_2\text{O}_5 = 41\% \)
This is a high-analysis, highly water-soluble fertilizer.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Diammonium phosphate (DAP) is the most widely used phosphatic fertilizer in India and globally.
It is a highly concentrated NP binary fertilizer.
Fertilizer standards are strictly regulated by quality control legislation, such as the Fertilizer Control Order (FCO) in India, which specifies the minimum nutrient contents and solubility requirements for commercial fertilizers.

Step 2: Detailed Explanation:
Let us analyze the chemical composition and legal standards for commercial DAP:
Total Nutrient Content: Standard commercial DAP contains \( 18\% \) nitrogen (\( \text{N} \)) and \( 46\% \) total phosphorus (expressed as phosphorus pentoxide, \( \text{P}_2\text{O}_5 \)).
Phosphorus Fractions: The total phosphorus in phosphatic fertilizers is divided into water-soluble, citrate-soluble, and citrate-insoluble fractions.
Plants can easily absorb water-soluble phosphorus, making it the most valuable fraction in the fertilizer.
Quality Standards: According to the Fertilizer Control Order (FCO) specifications for DAP:
- Minimum total nitrogen: \( 0\% \)
- Minimum total phosphate (as \( \text{P}_2\text{O}_5 \)): \( 40\% \)
- Minimum water-soluble phosphate (as \( \text{P}_2\text{O}_5 \)): 40%
This requirement ensures that at least \( 89\% \) of the total phosphorus in DAP (\( \frac{41}{46} \times 100 \approx 81\% \)) is in a highly soluble form that is readily available to crops immediately after application.
Therefore, the water-soluble \( \text{P}_2\text{O}_5 \) content in standard DAP is \( 40\% \) (commonly rounded or specified as \( 40\% \) to \( 46\% \) depending on the specific option listed in competitive exams, with \( 40 \) or \( 40.5 \) being the closest matching choices).

Step 3: Final Answer:
The water soluble P (as % $\text{P}_2\text{O}_5$) in diammonium phosphate (DAP) is 40.