The study looked at how different types of fertilizers affect the amount and distribution of organic nitrogen in soil. They used a method called the Bremner method to analyze the nitrogen in a brown soil after 29 years of fertilization. The results showed that using manure along with chemical fertilizer increased the amount of different forms of organic nitrogen, especially amino acid nitrogen. The order of nitrogen forms in the soil was amino acid nitrogen, non-hydrolysable nitrogen, ammonia nitrogen, unidentified hydrolysable nitrogen, and amino sugar nitrogen. The best way to maintain soil fertility and sustainable agriculture was found to be using manure with chemical fertilizer.