The present work investigates vitreous fertilizers for agricultural purposes. The studied compositions belong to K2O – MgO – P2O5 ternary system. The samples were investigated by IR and Raman spectroscopy, showing vibrations specific to P-O-P, PO32-, PO2 and P = O bonds. In the case of AG.5 sample, IR peaks are shifted, indicating that nitrogen replaces oxygen in a great extent that modifies the vitreous phosphate network. XRD plots revealed specific shapes for glassy state both for un-nitrided and nitrided samples. SEM investigations on powders show more homogeneous darker phases in the case of AG 5 sample comparatively to AG 2 series.