List of top Soil Science Questions on Soil Testing and Nutrient Extractants

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:

Parker et al. (1951) introduced the concept of Nutrient Index Value (NIV) to describe the fertility status of soils for the purpose of mapping. The NIV value of medium nutrient status is: