Effect of chicken manure and biochar on CO₂ and CH₄ emission in paddy fields in South China

The application of biochar to enhance soil carbon sequestration in farmlands is an increasingly investigated research to reverse the effects of climate change. There is little report on the effect of adding manure in situ in combination with biochar application to winter paddy fields on CO₂ and CH₄ emissions during winter fallow and growth period of double rice. To fully use winter fallow paddy fields and determine how biochar and chicken manure affected the emission of CO₂ and CH₄, four treatments were set up—no fertilization (CK), chicken raised in the field and chicken manure addition (C), in situ chicken manure addition and biochar addition (CB), and biochar addition (B). The CO₂ and CH₄ fluxes and total emissions were determined in paddy fields using the chamber method along with Greenhouse Gas Analyzer during winter and the growth period of double cropping rice. The objective was to assess the effects of chicken manure in situ incorporation and biochar on soil carbon emission. The results showed that relationship between CO₂ flux under CK and B treatments and soil temperature at 5 cm soil depth fitted well the non-linear index model. Then CO₂ flux under C and CB treatments had no significant correlation with soil temperature at 5 cm soil depth, which meant that the in situ addition of chicken manure made it more sophisticated for soil to modulate CO₂ emission. The treatment of in situ addition of chicken manure significantly increased soil CO₂ emission in winter paddy fields and during rice growth period with respective emissions of 9 935.39 kg·hm^-2 and 27 756.34 kg·hm^-2, which was 58.7 times (P < 0.01) and 56% (P < 0.05) higher than that of CK. The cumulative CO₂ emissions in winter paddy fields and during rice growth period under biochar addition were 12.3 times (P < 0.01) and 41% (P < 0.05) higher than that of CK during in winter paddy fields and during rice growth period. The emissions of CH₄ in winter paddy fields and during rice growth period under treatment of in situ addition of chicken manure were significantly higher than that under other treatments, while it was not significantly changed in winter paddy fields and significantly decreased during rice growth period under biochar addition treatments. Chicken manure in situ application in combination with biochar treatment also significantly improved CO₂ emission of paddy soils. Cumulative CO₂ emission under chicken manure in situ application along with biochar addition in winter paddy fields was significantly higher than that under chicken manure in situ application. Also during rice growth period, it was significantly lower than that under chicken manure return. This suggested that biochar addition inhibited soil CO₂ emission in the late period. The addition of biochar decreased soil CH₄ emission in both winter paddy field and rice growth stage. In short, the addition of exogenous organic carbon like chicken manure to soils increased carbon emission (both CO₂ and CH₄), while the addition of biochar to soils increased carbon emission in the short-term and decreased CH₄ emission. Therefore, from the longer time view, biochar application to soils was beneficial to soil carbon sequestration, and might mitigate carbon emission caused by in situ application of chicken manure.