TOTAL NITROGEN IN PLANT-MATERIAL DETERMINATED BY MEANS OF DRY COMBUSTION - A POSSIBLE ALTERNATIVE TO DETERMINATION BY KJELDAHL DIGESTION

The use of dry combustion-based analyzer (CHN-600, LECO Corporation, St. Joseph, MI) for nitrogen (N) determination in plant material is described. The method was evalueted in inter-laboratory proficiency test (International Plant-Analytical Exchange) and compared with results obtained by the Kjeldahl method. Differences between methods were small and results were in very close agreement. However when differences did occur, correction for nitrates did not fully explain differences between the two methods. A high content of nitrates can lead to serious differences between results obtained by the Dumas and Kjeldahl methods. Accuracy for the dry combustion method was tested with certified reference materials. Long-term evaluation of repeatability of a determination varied from 1% to 2% with respect to material analyzed or content of nitrogen.