A COMPARISON OF ANALYTICAL METHODS FOR NITROGEN ANALYSIS IN PLANT-TISSUES

Automated Dumas methods could replace Kjeldahl digestions for the anal ysis of nitrogen (N), but few comparisons of these methods for plant t issue are available. Because N nutrition usually affects tissue levels of N, the influence of analytical method (Dumas and a modified micro- Kjeldahl without salicylic acid pre-treatment) on N determination in l eaves and petioles of 'Shogoin' turnips grown under different N regime s was investigated. Dumas- and Kjeldahl-N ranged from 1.31 to 6.70% an d 1.22 to 5.77% in leaves and petioles, respectively, and Dumas-N was significantly (p<0.01) higher than Kjeldahl-N. This resulted in a tend ency to overrate N status when available thresholds developed with Kje ldahl-N values were use with Dumas-N data. However, for turnip, Kjelda hl-N could be estimated from Dumas-N in the 1-6% range as: Kjeldahl-N = -0.015 (p = 0.82) + 0.858 (p<0.001) Dumas-N (p<0.01, R2 = 0.98), and developing new interpretative data for Dumas N was not necessary.