Objective  Changes on the form and loss of nitrogen (N) in pig manure due to the addition of biochar during composting were investigated.

  Method  In a forced ventilation reaction box, effects of 0%, 3%, 6%, and 9% addition of biochar (on a dry weight basis) on N in composting pig manure were determined.

  Result  With the biochar addition, the total N and nitrate in the compost increased with time. The total N increased 3.68% to 5.43% by the end of the fermentation process, whereas, the total soluble and ammonium N increased initially and then declined afterward. Increasing biochar mitigated the decline on ammonium N. The rates of N loss by the treatments ranged from 20.69% to 28.18%. At 3% and 6% biochar addition, the ammonia volatilization on the compost were 8.98% and 46.30%, respectively, which were higher than without the addition. On the other hand, 9% of biochar produced the lowest N loss and ammonia volatilization.

  Conclusion  In the pig manure composting, the addition of biochar rapidly heated up the heap and maintained a high temperature for an extended period facilitating the fermentation and conversion of ammonia into nitrate. Increased biochar addition also promoted the nitrate formation. However, the presence of biochar in compost caused greater loss on N as the fermentation progressed.