The study was conducted in a long term fertilizer experiment set up on a Typic Haplustept in 1971 on the farm of Indian Agricultural Research Institute, New Delhi,  with maize (Zea mays) - wheat (Triticum aestivum) - cowpea (Vigna unguiculata) cropping sequence.  Apart from a control, treatments included optimum NPK level (100% NPK) as recommended according to initial soil test values , 50% NPK, and 150% NPK , 100% NP, 100% N, treatments involving NPK with FYM (for maize only), with Zn (for wheat only), with S and with hand weeding practice.  The effects of different treatments were investigated on soil nitrogen fractions. The long-term application of 100% NPK + FYM resulted in the highest amount of total N  in  soil which was closely followed by 150% NPK. While application of 150% NPK resulted in the highest amount of hydrolysable NH3-N and of NO3-N, amino acid N content was highest in soils under 100% NPK + S treatment. Amino acid-N and hydrolysable NH3-N were the dominant fractions of N in soil irrespective of treatment. Long term use of optimum dose of NPK either alone or in conjunction with FYM/S resulted in a significant increase in the amount of hydrolysable N fraction in soil. A significant increase in the total hydrolysable N, mainly through hydrolysable unknown N was observed during the cropping sequence.