Effect of biochar addition method on ammonia volatilization and quality of chicken manure compost

Composting chicken manure causes negative impacts on environmental ecosystem by increasing ammonia (NH 3 ) emissions.Split addition of maize straw-derived biochar (Bi) during composting of chicken manure may promote the composting process, increase the quality of produced compost and reduce NH 3 volatilization.To build composting piles, fresh chicken manure and maize straw were mixed (2:1 w/w).Biochar (10% w/w) was applied to the compost piles in different addition modes: one-time applied biochar (OTABi), 10% at the beginning of the trial, and split-applied biochar (SABi), 2.5% at 0, 3, 7 and 15 days of the composting.In addition to the control (without biochar) treatment, measurements of NH 3 emissions were performed in a bench-scale composting experiment.To evaluate the phytotoxicity and maturity of the compost, germination tests were performed in Petri dishes.Compared with the control and OTABi treatments, SABi had a great positive effect (by 40% and 33%) on the final general characteristics of the compost and reduced the cumulative NH 3 emissions.Although OTABi treatment had faster degradation during composting, it did not enhance humification.In the mature compost, the humic substances of SABi treatment were 17% and 40% higher than control and OTABi treatments.In addition, in SABi, the values of humic acid carbon (HAC) and humification index (HI) were significantly higher than in other treatments.By the end of composting, both biochar application modes exhibited low water-extractable organic carbon and high seed germination index compared with the control treatment.This study suggests that during chicken manure composting split application of biochar is a crucial practice for reducing N loss, mitigating NH 3 emissions and enhancing humification.