Net global warming potential, greenhouse gas intensity and carbon footprint as affected by different tillage systems from Chinese double-cropping paddy fields

https://doi.org/10.1016/j.still.2021.104947Get rights and content

Highlights

  • RT practice are promising in rice production for higher grain yield with similar GHGI and CF.

  • CH4 was largest contribution to NGWP, GHGI and CF in paddy field.

  • CH4 emissions were conspicuously correlated with SOC content below 5 cm soil depth.

  • NT practice tended to reduce SOC sequestration with the increase of soil depth.

Abstract

Conservation tillage may be an alternative system for rice production in China, yet differences in net global warming potential (NGWP), greenhouse gas intensity (GHGI) and carbon footprint (CF) among different tillage methods are poorly documented. Accordingly, a 3-year field experiment was conducted to simultaneously measure methane (CH4) and nitrous oxide (N2O) emissions and changes in soil organic carbon (SOC) under conventional tillage (CT), reduced tillage (RT) and no-tillage (NT) methods in Chinese double-rice cropping systems. There was no difference in SOC content among the tillage treatments, but SOC sequestration under NT reduced obviously with the increase of soil depth at 0∼20 cm. CH4 emissions were conspicuously correlated with SOC content at soil depth below 5 cm. Tillage methods had no significant effect on N2O emission, except for the substantial N2O emission under NT during non-rice season. Compared with the NT plots, the annual CH4 emission and NGWP were significantly increased in the CT and RT plots over the three years. There were no significant differences among the tillage methods with respect to GHGI and CF, whereas the grain yields were greatly increased in the RT plot. We conclude that RT practice are promising in rice production for higher grain yield with similar GHGI and CF, while increasing productivity of the NT system is a high priority since the CH4 emission and NGWP can be dramatically reduced.

Introduction

Global warming is one of the major consequences of the human activities associated with increasing concentration of atmospheric greenhouse gas (GHG) emission, such as nitrous oxide (N2O), methane (CH4) and carbon dioxide (CO2) (Shakoor et al., 2021). Among anthropogenic activities, agriculture is estimated to be accountable for 12 % of total GHG emissions (IPCC, 2014). Agricultural management practices can affect emission of GHG, directly and indirectly, from agricultural inputs that include tillage, fertilizer, irrigation, seeding, storage, and harvest (Xue et al., 2014; Chen et al., 2018; Zhou et al., 2019).

Rice is the staple food for nearly 50 % of the world's people, mainly in Asia. Conservation tillage (such as no-tillage (NT) or reduced tillage (RT)) has been increasingly used in paddy fields in Asia, especially in southern China (Zhang et al., 2013). In agricultural soils, reducing net CO2 emissions is synonymous with increasing soil carbon storage – a process usually referred to as carbon sequestration (Gong et al., 2021). Many studies have indicated that conservation tillage systems enhance soil carbon sequestration, notably in the soil surface layer (van Groenigen et al., 2011; Zhang et al., 2015). However, agricultural GHG fluxes are complex and involve many interrelated trade-offs. For example, higher soil carbon sequestration often causes substantial N2O and CH4 emissions from rice paddies (Zou et al., 2005; Ma et al., 2009). Our previous studies also found significant linear relationships between CH4 emissions and soil organic carbon (SOC) content (Shang et al., 2011), which means that SOC sequestration stimulated CH4 emissions from rice paddies. Consequently, it is necessary to comprehensively evaluate the effects of different tillage methods on GHGs emissions in intensive rice production.

The net exchange of CH4, N2O and CO2 in terms of CO2 equivalents between soils and the atmosphere comprises the net global warming potential (NGWP) of a cropping system (Robertson and Grace, 2004), which can also be expressed on the basis of per unit of yield (greenhouse gas intensity, GHGI) (Mosier et al., 2006). Some studies have indicated that NT decreased GHG emissions and maintained grain yields, thus resulting in a lower GHGI as compared with conventional tillage (CT) in paddy fields (Zhang et al., 2016). However, it is also now recognized that merely focusing on soil borne GHGs may not represent the actual impact of cultivation practices owing to significant emissions associated with farm activities (Lal, 2004). Generally, NT mitigated carbon emissions due to no mechanical tillage compared to CT and RT (Zhang et al., 2016). It is therefore essential to expand the boundary of GHG accounting for agriculture to include all relevant activities contributing to GHG fluxes. For this purpose, carbon footprint (CF), which represents total GHG emissions accumulated during an activity, acts as a useful indicator (Xue et al., 2016). Agronomic modifications like reduction in tillage intensity are being popularized as a low input agriculture (Ogle et al., 2012; Zhang et al., 2016; Shakoor et al., 2021), but responses of conservation tillage with respect to CF assessment, particularly in rice production have received less attention.

The lower Yangtze River is a typical double-rice cropping area, accounting for 40 %–60 % of the arable land and emit about 50 % of the total CH4 from paddy fields in China (Zhang et al., 2011). Due to the important role of rice production in global agriculture, adopting reasonable agricultural management is of great significance to mitigate global GHG emissions. There has been an increasing amount of studies SOC sequestration and GHG emissions in paddy fields, but the comprehensive impacts of different tillage practices on NGWP, GHGI and CF are not well documented in typical double rice-cropping systems. Therefore, we studied the rice grain yield, SOC content, and emissions of CH4 and N2O from a double rice-cropping field in Jiangxi Province, southeast China from April 2013 to April 2016 under different tillage practices with the incorporation of crop residues. The objectives of this study were to clarify the effects of tillage methods on the sequestration of SOC and the emissions of CH4 and N2O from the double rice-cropping systems and to evaluate their effects on the NGWP, GHGI and CF.

Section snippets

Experimental site

A 3-year field experiment was initiated in April 2013 at Wenzhen agro-technical demonstration farm in Jinxian County, Jiangxi Province, China (28°20′10″N, 116°5′28″E), where the cropping regime is dominated by double rice-cropping systems. The region is characterized by subtropical humid monsoon climate, with an annual average air temperature of 17.5 °C, precipitation of 1587 mm, sunshine of 1900−2000 h, and frost-free period of 282 days. The monthly rainfall, maximum and minimum temperatures

CH4 emission

During the early-rice growing seasons from 2013 to 2015, the CH4 fluxes of different treatments increased gradually in the early growth stage, and decreased slowly at the end of growth stage (Fig. 2). The fluxes of CH4 showed a slight peak in the midseason for the different plots. Seasonal total of CH4 emissions significantly varied with tillage, year and their interaction in the early-rice growing season (Table 2). Averaged CH4 emission was significantly lower in the 2013 early-rice season

SOC sequestration under different soil layer as affected by tillage practices in double rice-cropping systems

The topsoil (0∼20 cm) SOC content was 23.6 g kg−1 after experiments, which was highly comparable to the previous estimates of regional or national mean SOC content of paddy soils (Liao et al., 2009; Yang et al., 2018). Consistent with previous reports, the double rice-cropping systems have experienced increases in topsoil SOC density over the treatments under rice straw returning. Annual increase rate of SOC averaged 0.38∼0.74 g C kg−1 yr−1 in this study, which falls within the range of

Conclusions

Taking effective agriculture management strategy for mitigating climatic impacts requires a complete perspective on the agriculture impacts on GHG emissions while obtain high yield. Our results showed that the tillage methods had significant effects on the emissions of CH4 and N2O and vertical distribution of SOC. CH4 emissions were conspicuously correlated with SOC content at soil depths below 5 cm. The NGWP, GHGI and CF were dominated by CH4 emissions in the double rice-cropping systems. High

Declaration of Competing Interest

The authors report no declarations of interest.

Acknowledgements

This work was generously supported by the National Natural Science Foundation of China (31960626, 31601833) and the Science and Technology Landing Plan of Colleges and Universities in Jiangxi Province (KJLD12063).

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