Question

Bray No. 1 is

• A. $0.5\,\text{M }\text{NaHCO}_3$ at $\text{pH } 8.5$
• B. $0.5\,\text{N }\text{NaHCO}_3$ at $\text{pH } 8.5$
• C. $0.03\,\text{M }\text{NH}_4\text{F} + 0.025\,\text{N }\text{HCl}$
• D. $0.03\,\text{N }\text{NH}_4\text{F} + 0.025\,\text{N }\text{HCl}$

Hint:

Remember the diagnostic extractants for available Phosphorus:
- Acid soils $\rightarrow$ Bray No. 1 ($0.03\,\text{N }\text{NH}_4\text{F} + 0.025\,\text{N }\text{HCl}$)
- Alkaline/Neutral soils $\rightarrow$ Olsen's reagent ($0.5\,\text{M }\text{NaHCO}_3$ at $\text{pH } 8.5$)

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Bray No. 1 is a chemical extractant developed by Bray and Kurtz (1945) to estimate plant-available phosphorus in acidic to neutral soils.

Step 2: Detailed Explanation:
- The Bray No. 1 extracting solution consists of a mixture of ammonium fluoride ($\text{NH}_4\text{F}$) and hydrochloric acid ($\text{HCl}$).
- The standard chemical concentration of this extractant is $0.03\,\text{N \text{NH}_4\text{F}$ and $0.025\,\text{N }\text{HCl}$}.
- Role of $\text{F^-$ ion:} Fluoride ions form complexes with aluminum ($\text{Al}^{3+}$), which releases the phosphate adsorbed to aluminum oxides.
- Role of $\text{H^+$ ion:} The dilute acid dissolves calcium-bound phosphates and prevents the readsorption of released phosphate onto clay minerals.
- Options (A) and (B) describe Olsen's extractant, which is used for neutral to alkaline soils.

Step 3: Final Answer:
The composition of Bray No. 1 is $0.03\,\text{N }\text{NH}_4\text{F} + 0.025\,\text{N }\text{HCl}$.