Effects of land use conversion and fertilization on CH4 and N2O fluxes from typical hilly red soil

Abstract

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 (CH 4 ) and nitrous oxide (N 2 O) 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 CH 4 fluxes at the expense of increasing the N 2 O fluxes. Furthermore, fertilization significantly decreased the CH 4 fluxes from paddy soils in the second stage after conversion, but it failed to affect the CH 4 fluxes from orchard soils, whereas fertilizer applied to orchard and paddy increased soil N 2 O emissions by 68 and 113.9 %, respectively. Thus, cumulative CH 4 emissions from the OF were 100 % lower, and N 2 O emissions were 421 % higher than those from the PF. Although cumulative N 2 O emissions were stimulated in the newly converted orchard, the strong reduction of CH 4 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 (NH 4 + -N) and nitrate (NO 3 − -N) contents indicated a significant variation in soil properties and contributed to variations in soil CH 4 and N 2 O 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 CH 4 and N 2 O. Nevertheless, more field measurements from newly converted orchard are highly needed to gain an insight into national and global accounting of CH 4 and N 2 O emissions.

Responses of CH4 and N2O fluxes to land-use conversion and fertilization in a typical red soil region of southern China

“…The mean annual CH 4 and N 2 O fluxes from rice paddies in this study were 303.9 kg C ha −1 and 3.8 kg N ha −1 , respectively, over the three cultivation years. These values were within the ranges identified by previous studies in double rice-cropping system with similar fertilization rates 6 , 9 , 28 , 37 , but were much higher than those from other studies in single rice-cropping systems 3 , 15 , 38 . The mean annual CH 4 and N 2 O fluxes from the paddy field-converted citrus orchard were −1.19 kg C ha −1 and 10.88 kg N ha −1 , respectively, over the entire study period, which were generally close to previous observations 18 , 39 , 40 .…”

“…The periodic waterlogging-drainage alteration episodes and intensive inputs of organic material and nitrogen fertilizer in paddy fields may provide a suitable soil environment and accessible substrate for CH 4 and N 2 O emissions 3 , 4 . Many studies have demonstrated high CH 4 but relatively low N 2 O emissions from rice paddies because anaerobic conditions limit nitrate availability and because strict anaerobiosis favours complete denitrification to nitrogen gas (N 2 ) 5 , 6 . However, N 2 O emissions are generally high in upland soils, especially after fertilization or irrigation events, due to the tight coupling between nitrification and denitrification 7 – 9 .…”

“…The high variability of soil CH 4 and N 2 O fluxes due to land-use change is associated with particular site conditions, such as the soil type and microclimate, the type and history of land-use change, and the management practices used 16 – 18 . In general, conversion from rice paddy to upland agriculture can significantly reduce CH 4 emissions or even convert the soil from an emission source to a sink for atmospheric CH 4 6 , 9 . However, when and to what extent can the soil act as an atmospheric CH 4 sink after these land-use conversions still remain unclear.…”

“…China is one of the most important rice-producing countries in the world, accounting for 20% of the global rice production area 6 , 22 . The annual totals for CH 4 and N 2 O emissions from Chinese rice paddies were approximately 4.5–7.5 Tg C yr −1 and 32–51 Gg N yr −1 , respectively, based on long-term field measurements and model simulations 22 – 25 .…”

“…During the past decades, the red soil regions, which are the most densely populated, have experienced significant changes in land use due to increased socio-economic development and demand for livestock products. In particular, conversion of rice paddies to upland cultivation for growing vegetables, fruits and economic forest has been locally advocated to meet increasing market demands and gain higher economic returns in these regions 6 , 18 . Such conversions not only can alter the physical, chemical and biological properties of the soil, but also can impact on the soil C and N turnover and GHG emissions.…”