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Modeling transformation dynamics of organic N to inorganic N during the storage or treatment of manure can provide insights for both manure nutrient management and environmental protection. A 60-day experiment was conducted to determine the transformation process from organic N to inorganic N under aerated and anaerobic conditions. Fresh dairy manure was treated at three temperatures (5, 20 and 30 C), with each treatment having three replicates. Sampling frequency reduced gradually, from daily at the beginning, to once every five days toward the end of the experiment. TKN and TAN were measured in the samples. The results showed that at 5, 20 and 30 oC accordingly, 71%, 77% and 89% of organic N decayed under anaerobic condition, and 79%, 85% and 92% of organic N decayed under aerated condition. A developed dynamic model featuring varying reaction orders was used to simulate the decay process with average error ranging from 7.8% to 17.4%. The fitness range was much better than with the models of conventional zero, first, and second reaction orders. Application of the model was also illustrated. 1. Experiment