Sulfuric Acid–selenium Digestion for Multi-Element Analysis in a Single Plant Digest

At the ICRISAT soil chemistry laboratory, a sulfuric acid-selenium (Se) digestion method has been used for several years for the determination of nitrogen (N) and phosphorus (P) in a single plant digest. The method is simple and was evaluated for determining N, P, potassium (K), calcium (Ca) and magnesium (Mg) in plant samples using a single digest. Finely ground plant materials of pigeonpea (Cajanus cajan) and rice (Oryza sativa) plant samples were digested at 370°C. Digestion completed in about 2.5 h when the digests were clear and colourless. Results with plant samples having a wide range in elemental concentrations showed that there was an excellent agreement in the values of various elements determined by the proposed digestion procedure and the routinely used Kjeldahl and triacid acid digestion methods. These results suggest that sulfuric acid-Se mixture can be used for preparing plant digests for determination of N, P, K, Ca and Mg in a single digest. In addition, this method is adapted for preparing plant digests for automated determination of N and P in plant samples using a Technicon Autoanalyser II.