A single plant tissue digestion for macronutrient analysis

A method was tested for determinations of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) in one single digestion of plant tissue. Traditionally, for determinations of these five elements in plant tissue, at least two digestion or ashing procedures are used, totaling about 6 hours of tissue mineralization time. The method tested involved using a digesting medium of concentrated H2SO4 and a mixed catalyst of Na2SO4 and CuSO4. The total digestion time was about 60 minutes on a hot plate. After tissue digestion, determinations were by volumetric analysis (N), colorimetry (P), and atomic absorption (Ca, Mg) or emission spectrophotometry (K). Leaves of eight different species, including one standard tomato leaf sample and one internal quality-control apple leaf sample were analyzed. High correlations occurred between the results obtained with the new procedure and with the standard digesting methods (furnace ashing and Kjeldahl digestion). The new method used much less reagents, electrical energy, and labor than standard methods. The new method appears acceptable for routine macronutrient analysis.