The invention relates to a process for the production of plant growth stimulator from fly ash, comprising treating fly ash with effluent NOx gases in a reactor under agitation at a temperature in the range of 60 to 100 degree celsius, for a time period in the range of 2 to 5 hours and treating the resulting material with effluent ammonia gas in the same reactor under ambient conditions for time period in the range of 20 to 50 minutes.