NITROGEN (TOTAL AND N-15) UPTAKE BY BARLEY AND WHEAT UNDER 2 IRRIGATION REGIMES

Nitrogen (total and N-15) uptake by barley (Hordeum vulgare L., cv. 'W alfajr') and wheat (Triticum aestivum L., cv. 'Karaj I') plants subjec ted to water stress were studied at the College of Agriculture, Univer sity of Tehran Experimental Farm located in the city of Karaj, Iran. T he treatments consisted of two irrigation intervals, 7 days (control) and 14 days (stress). The plants were at the reproductive stage of gro wth at the start of the N-15 treatment. Nitrogen (N-15) was applied to 1m x 1m plots selected at the center of the 2.5m x 2.5m main plots. T he N-15 was provided to plants by adding 250 mg N-15 as (NH4)(2)SO4 (5 .1 Atom % N-15) dissolved in water to each plot. The N-15 treatment pe riod continued for 48 hours. The plants were harvested at 6-hour inter vals during the N-15 treatment period. After each harvest, the straw a nd the grains were separated, oven dried at 65 degrees C and dry weigh ts were recorded. Plant materials were ground in a Wiley Mill to pass through a 2mm sieve for chemical analysis. Total N was measured by an Auto-Analyzer after Kjeldahl digestion, and N-15 was measured using a mass spectrometer. Nitrogen (total-N and N-15) content of both plant s pecies decreased under stress, with wheat appearing more severely affe cted than barley. However, nitrogen concentration was slightly higher for the stressed plants as compared with the controls. This pattern wa s essentially similar for both plants.