Land use conversion and fertilization have been widely reported to be important managements affecting the exchanges of greenhouse gases between soil and atmosphere. For comprehensive assessment of methane (CH4) and nitrous oxide (N2O) fluxes from hilly red soil induced by land use conversion and fertilization, a 14-month continuous field measurement was conducted on the newly converted citrus orchard plots with fertilization (OF) and without fertilization (ONF) and the conventional paddy plots with fertilization (PF) and without fertilization (PNF). Our results showed that land use conversion from paddy to orchard reduced the CH4 fluxes at the expense of increasing the N2O fluxes. Furthermore, fertilization significantly decreased the CH4 fluxes from paddy soils in the second stage after conversion, but it failed to affect the CH4 fluxes from orchard soils, whereas fertilizer applied to orchard and paddy increased soil N2O emissions by 68 and 113.9 %, respectively. Thus, cumulative CH4 emissions from the OF were 100 % lower, and N2O emissions were 421 % higher than those from the PF. Although cumulative N2O emissions were stimulated in the newly converted orchard, the strong reduction of CH4 led to lower global warming potentials (GWPs) as compared to the paddy. Besides, fertilization in orchard increased GWPs but decreased GWPs of paddy soils. In addition, measurement of soil moisture, temperature, dissolved carbon contents (DOCs), and ammonia (NH4+-N) and nitrate (NO3--N) contents indicated a significant variation in soil properties and contributed to variations in soil CH4 and N2O fluxes. Results of this study suggest that land use conversion from paddy to orchard would benefit for reconciling greenhouse gas mitigation and citrus orchard cultivation would be a better agricultural system in the hilly red soils in terms of greenhouse gas emission. Moreover, selected fertilizer rate applied to paddy would lead to lower GWPs of CH4 and N2O. Nevertheless, more field measurements from newly converted orchard are highly needed to gain an insight into national and global accounting of CH4 and N2O emissions.
Keywords: Fertilization; Global warming potentials; Land use conversion; Methane; Nitrous oxide.