N_2O emissions and nitrogen transformation during windrow composting of dairy manure

摘要

Windrow composting involves piling and regularly turning organic wastes in long rows, being in the succession of static standing periods between two consecutive pile turnings as well as a period of pile turning. N_2O emissions and N transformation were investigated during the processes of windrow composting. In contrast to the conventional understanding, we observed that N_2O concentrations inside compost materials were significantly higher after pile turning (APT) than before pile turning (BPT). Pile turning triggered a burst of N_2O production rather than simple gaseous N_2O escape from the stirred compost. Denitriftcation was the dominant pathway in pile turning because the observed NO2~ and NO3" concentrations were significantly lower APT compared to BPT. The sudden exposure of O2 severely inhibited N_2O reductase, which can block the transformation of N_2O to N2 and thus caused an increase of N_2O emission. As the NO_2~- and NO_3~- concentrations rose during the following 48 standing hours, nitrification dominated N transformation and did not cause an increase of surface N_2O emissions. Thus, pile turning resulted in a dramatic conversion of N transformation and strongly influenced its flux size. It was also found that high NO_2~- was accumulated in the compost and had a strong correlation with N_2O emissions. Practical methods regulating nitrite and the frequency of pile turning would be useful to mitigate N_2O emissions in manure composting.