Greenhouse gas emissions and global warming potential of traditional and diversified tropical rice rotation systems

Abstract

Global rice agriculture will be increasingly challenged by water scarcity, while at the same time changes in demand (e.g. changes in diets or increasing demand for biofuels) will feed back on agricultural practices. These factors are changing traditional cropping patterns from double-rice cropping to the introduction of upland crops in the dry season. For a comprehensive assessment of greenhouse gas (GHG) balances, we measured methane (CH4 )/nitrous oxide (N2 O) emissions and agronomic parameters over 2.5 years in double-rice cropping (R-R) and paddy rice rotations diversified with either maize (R-M) or aerobic rice (R-A) in upland cultivation. Introduction of upland crops in the dry season reduced irrigation water use and CH4 emissions by 66-81% and 95-99%, respectively. Moreover, for practices including upland crops, CH4 emissions in the subsequent wet season with paddy rice were reduced by 54-60%. Although annual N2 O emissions increased two- to threefold in the diversified systems, the strong reduction in CH4 led to a significantly lower (P < 0.05) annual GWP (CH4 + N2 O) as compared to the traditional double-rice cropping system. Measurements of soil organic carbon (SOC) contents before and 3 years after the introduction of upland crop rotations indicated a SOC loss for the R-M system, while for the other systems SOC stocks were unaffected. This trend for R-M systems needs to be followed as it has significant consequences not only for the GWP balance but also with regard to soil fertility. Economic assessment showed a similar gross profit span for R-M and R-R, while gross profits for R-A were reduced as a consequence of lower productivity. Nevertheless, regarding a future increase in water scarcity, it can be expected that mixed lowland-upland systems will expand in SE Asia as water requirements were cut by more than half in both rotation systems with upland crops.

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

“…Meanwhile, N 2 O emissions were generally higher in optimum soil moisture and N supply as a result of tight coupling between nitrification and denitrification (Snyder et al 2009). Those results were in well agreement with earlier studies (Knox et al 2015;Weller et al 2016) showing that the formation of aerobic conditions caused by land use conversion could result in the reduced CH 4 fluxes at the expense of increasing N 2 O fluxes (Jiang et al 2009). In our study, episodic higher CH 4 emission still occurred in the early conversion days (Fig.…”

“…In the present study, based on the agricultural practices, some crop residue was typically retained in paddy fields, which led to high level of soil DOC concentration throughout the observing period (Table 2). While in orchard fields, soil DOC contents decreased due to the improved soil aeration and increased mineralization activity (Weller et al 2016). Thus, our result confirmed that higher CH 4 fluxes were observed from paddy soils where DOC contents were higher (Zou et al 2005;Yao et al 2012).…”

“…However, results from current studies were not consistent, ranging from a large increase (Weller et al 2016) to a decrease (Jiang et al 2009) or to no significant impact (Inubushi et al 2003) on soil CH 4 and N 2 O fluxes. The large variability in the effect of land use change on soil CH 4 and N 2 O fluxes was likely linked to specific site conditions, such as soil type, the type of land use change, and management practice used (Inubushi et al 2003;Lin et al 2012).…”

“…In the past decades, significant lower CH 4 emissions but higher N 2 O emissions were usually observed from upland soils as compared to paddy soils (Jiang et al 2009;Weller et al 2016). However, most of the previous studies emphasized the comparison of CH 4 and N 2 O fluxes in different land use types and did not consider the process of land use conversion (Jiang et al 2009;Lin et al 2012;Zona et al 2013).…”

“…The periodic waterlogging-drainage alteration episodes and intensive fertilizer inputs in paddy field could provide suitable soil environment and accessible substrate for CH 4 and N 2 O emissions (Hou et al 2012;Yao et al 2012). While paddy soils release substantial amounts of CH 4 and N 2 O to the atmosphere, the changes in agriculture land use could have potentials for mitigating net global warming potential by decreasing CH 4 and/or N 2 O emissions (Weller et al 2016).…”