Soil extractants used for available nutrients:
(A) 2 M KCl extract is used for determination of mineral N (NH₄ and NO₃) using soil:solution ratio of 1:10.
(B) DTPA extractant (pH 7.5) is used for determination of micronutrients using soil:solution ratio of 1:20.
(C) Ammonium acetate (1 N) solution is used for determination of potassium using soil:solution ratio of 1:5.
(D) Olsen reagent (0.5 M NaHCO₃, pH 8.5) is used for determination of available P in soil using soil:solution ratio of 1:20.
Choose the correct answer from the options given below:

Question

Which of the following statements is false?

Answer 1

This question tests whether you remember the exact reagent, pH and soil to solution ratio fixed for each standard soil test, since a small change in any one of these numbers turns a correct method into a wrong one.

(A) 2 M KCl for mineral N at 1:10: Correct. Potassium chloride solution pulls out both ammonium and nitrate forms of nitrogen, and the fixed ratio for this test is 1:10.
(B) DTPA at pH 7.5 for micronutrients at 1:20: Wrong. The DTPA test for zinc, copper, iron and manganese runs at pH 7.3, and the soil to solution ratio is 1:2, not 1:20, so both numbers here are off.
(C) Ammonium acetate (1 N) for potassium at 1:5: Correct. Neutral normal ammonium acetate at a 1:5 ratio is the accepted method for available potassium.
(D) Olsen reagent for available P at 1:20: Correct. Olsen's 0.5 M sodium bicarbonate at pH 8.5 is used for available phosphorus, at the standard 1:20 ratio.

Since (B) carries a wrong pH and a wrong ratio while (A), (C) and (D) all state the correct reagent, pH and ratio, only (A), (C) and (D) hold true together.

Let's summarize:

DTPA works at pH 7.3 with a 1:2 soil to solution ratio, not pH 7.5 or 1:20.
KCl for nitrogen, ammonium acetate for potassium and Olsen reagent for phosphorus are all stated correctly in the question.

So the answer is (A), (C) and (D) only, option 4.

Answer 2

This question tests whether you remember the exact reagent, pH and soil to solution ratio fixed for each standard soil test, since a small change in any one of these numbers turns a correct method into a wrong one.

(A) 2 M KCl for mineral N at 1:10: Correct. Potassium chloride solution pulls out both ammonium and nitrate forms of nitrogen, and the fixed ratio for this test is 1:10.
(B) DTPA at pH 7.5 for micronutrients at 1:20: Wrong. The DTPA test for zinc, copper, iron and manganese runs at pH 7.3, and the soil to solution ratio is 1:2, not 1:20, so both numbers here are off.
(C) Ammonium acetate (1 N) for potassium at 1:5: Correct. Neutral normal ammonium acetate at a 1:5 ratio is the accepted method for available potassium.
(D) Olsen reagent for available P at 1:20: Correct. Olsen's 0.5 M sodium bicarbonate at pH 8.5 is used for available phosphorus, at the standard 1:20 ratio.

Since (B) carries a wrong pH and a wrong ratio while (A), (C) and (D) all state the correct reagent, pH and ratio, only (A), (C) and (D) hold true together.

Let's summarize:

DTPA works at pH 7.3 with a 1:2 soil to solution ratio, not pH 7.5 or 1:20.
KCl for nitrogen, ammonium acetate for potassium and Olsen reagent for phosphorus are all stated correctly in the question.

So the answer is (A), (C) and (D) only, option 4.

Show Hint

The Correct Option is D

Solution and Explanation

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