The introduction of magnesium atoms into Li3N lattice yields 13 NMR signals for 7Li which is the greatest number of lines ever measured in a wide line NMR spectrum for I= 3/2. The comparison with theoretical first order quadrupole spectra allowed the observation of an additional satellite system and the quantitative calculation of the changes of the asymmetry parameters. It was found, that all changes in the Li3N spectrum on introduction of magnesium atoms occur in the range of the lithium satellite lines, which belong to weaker bound lithium atoms outside those lattice planes containing the nitrogen atoms.