Effect of Integrated Nitrogen Management on Forage Yield of Multicut Sorghum, Available Nitrogen and Microbial Count in the Soil

In a field experiment conducted during 2004 and 2005, application of 75 kg N ha⁻¹ through chemical fertilizer + 25 kg N ha⁻¹ through FYM or castor cake recorded significantly higher green forage yield and crude protein content of forage sorghum than the other treatments. Application of 100% N through organic manures (50 kg N ha⁻¹ through FYM + 50 kg N ha⁻¹ through castor cake) was significantly inferior in forage production, but could significantly increase the available N content and microbial count in the soil as compared to 100% N through chemical fertilizer. The maximum green forage and crude protein content of forage sorghum as well as available N content in the soil were recorded under Azotobacter + Azospirillum inoculation, although the effect on green forage yield was non-significant. The Azotobacter and Azospirillum counts were increased significantly under Azotobacter and Azospirillum inoculation treatments, respectively, while no bio-fertilizer inoculation recorded significantly lower values of soil available N as well as Azotobacter and Azospirillum population. Integration of organic and inorganic fertilizers along with bio-fertilizer inoculation increased the Azotobacter and Azospirillum population in the soil rhizosphere during both the years and enhanced the soil available N status in 2004. Application of 100% N through organic manure and dual inoculation of Azotobacter and Azospirillum registered the highest Azotobacter and Azospirillum population.