Which instrument is used for determination of K content in soil?

Correct option is C

The correct answer is (C) Flame photometer

Explanation:
• The Flame Photometer (Flame Emission Spectrometer) is the standard instrument used in soil testing laboratories for the estimation of Potassium (K) and Sodium (Na).
• The principle is based on emission spectroscopy: when a soil extract (usually using Neutral Normal Ammonium Acetate) is aspirated into a flame, the K atoms are excited. As they return to their ground state, they emit light of a specific wavelength (characteristic violet-red color for K).
• The intensity of the emitted light is directly proportional to the concentration of the element in the sample.
• It is preferred for K because it is relatively inexpensive, fast, and highly sensitive for alkali metals.

Information Booster:
• For K determination, the flame photometer uses a specific filter that allows light of 766 nm wavelength to pass.
• Available Potassium in soil is generally extracted using the Hanway and Heidel method (1N Ammonium Acetate, pH 7.0).
• Regular calibration using standard KCl solutions is necessary for accurate results.

Additional Knowledge:
• UV-VIS Spectrophotometer (Option A): Commonly used for determining Phosphorus (P) content via the colorimetric molybdenum blue method.
• Atomic Absorption Spectrophotometer (AAS) (Option B): Used for micronutrients like Zn, Fe, Cu, and Mn. While it can measure K, it is often overkill and more expensive than flame photometry.
• Colorimeter (Option D): Used for many chemical tests but lacks the flame excitation source needed for standard K analysis.