We present detailed spectroscopic analysis of nitrogen abundances in 31 unevolved metal-poor stars analysed by spectral synthesis of the near-UV NH band at 3360 Å observed at high resolution with various telescopes .
We found that [ N/Fe ] scales with that of iron in the metallicity range -3.1 < [ Fe/H ] < 0 with the slope 0.01 \pm 0.02 .
Furthermore , we derive uniform and accurate ( N/O ) ratios using oxygen abundances from near-UV OH lines obtained in our previous studies .
We find that a primary component of nitrogen is required to explain the observations .
The NH lines are discovered in the VLT/UVES spectra of the very metal-poor subdwarfs G64-12 and LP815-43 indicating that these stars are N rich .
The results are compared with theoretical models and observations of extragalactic HII regions and Damped Ly \alpha systems .
This is the first direct comparison of the ( N/O ) ratios in these objects with those in Galactic stars .