The KCl extraction method is commonly used to extract inorganic nitrogen (including ammonium, nitrate, and nitrite) from soil samples.
KCl Extraction for Inorganic Nitrogen: A 2M KCl solution serves as the extractant for inorganic nitrogen in soil samples. Here’s how the process works:Ammonium (NH₄⁺): Exchangeable ammonium is most commonly extracted from moist soil samples immediately after sampling using 2M KCl. This extraction method ensures quantitative extraction of NH₄⁺ without interacting with exchangeable nitrogen. Nitrate (NO₃⁻): Nitrate is water-soluble and extracted by the KCl solution. It provides a reliable method for measuring NO₃⁻ concentrations in soil. Nitrite (NO₂⁻): Nitrite is seldom present in detectable amounts in neutral to alkaline soils, except in fertilized conditions. However, the KCl extraction method does not specifically target nitrite. The KCl extraction solution is recommended because it provides quantitative extraction of inorganic nitrogen, does not interact with exchangeable nitrogen, and can be safely stored before analysis. The extracted samples should ideally be analyzed within 24 hours, but frozen KCl extracts can be stored indefinitely.
Procedure for KCl Extraction: Here’s a simplified procedure for extracting inorganic nitrogen using KCl:Weigh 10 grams (5 grams for organic horizons) of 2 mm sieved soil into a 50 mL screw cap centrifuge tube. Add 30 mL of 1M KCl solution to the tube. Place the tube on a shaker for 30 minutes at 200 rpm. Let the samples sit for an additional 30 minutes. Filter the samples using a Whatman #42 filter (2.5 μm pore size). Analyze the filtrate for inorganic nitrogen (NH₄⁺, NO₃⁻) and exchangeable acidity.
Please note this method primarily targets ammonium and nitrate, while nitrite is not specifically quantified using the KCl extraction. If you need to measure nitrite separately, consider alternative methods.