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No-till (NT) has been widely regarded as a potential option to enhance soil organic carbon (SOC) sequestration and thus mitigate climate change. However, recent studies have shown that previous estimates of SOC storage under NT seem to be overestimated due to shallow sampling and improper SOC accounting. In China, the overall trend and magnitude of changes in SOC storage in response to NT adoption remain inconclusive. Here we use a meta-analysis to assess the relative change in SOC storage (profiles ≥20 cm) based on 95 comparisons between NT and conventional tillage (CT) from 57 experimental sites (≥3 years) covering various cropping systems, soil types, and climatic regions of China. The results revealed that compared to CT, adopting NT led to SOC accumulation in the upper 20 cm layer and SOC depletion in the 30–40 cm layer. On average, NT improved SOC stocks over CT by 3.8% [95% confidence interval (CI): 1.4%–6.3%; P = 0.005] and 5.1% (95%CI: 2.5%–7.7%; P < 0.001) as represented by the equivalent soil mass (ESM) and fixed-depth (FD) approaches, respectively. The relative change in SOC storage rate under NT over tilled soil for the top 30 cm layer was therefore significantly higher ( Mean : 0.300 Mg ha −1 yr −1 , 95%CI: 0.054–0.547; P < 0.001) calculated by FD approach than that by ESM ( Mean : 0.141 Mg ha −1 yr −1 , 95%CI: −0.102–0.384; P = 0.100). Further analysis suggested that the effect of NT on SOC storage was significant with residue retained‎, double cropping systems, and in the coarse textured soils. We conclude that although NT was an effective agronomy option for soil conservation in China, the potential for mitigation climate change through increased SOC sequestration by NT should not be amplified. [ABSTRACT FROM AUTHOR]

Abstract: For thousands of years, the Huang-Hai Plain in northeast China has been one of the most productive agricultural regions of the country. The future of this region will be determined in large part by how global climatic changes impact regional conditions and by actions taken to mitigate or adapt to climate change impacts. One potential mitigation strategy is to promote management practices that have the potential to sequester carbon in the soils. The IPCC estimates that 40Pg of C could be sequestered in cropland soils worldwide over the next several decades; however, changes in global climate may impact this potential. Here, we assess the potential for soil C sequestration with conversion of a conventional till (CT) continuous wheat system to a wheat–corn double cropping system and by implementing no till (NT) management for both continuous wheat and wheat–corn systems. To assess the influence of these management practices under a changing climate, we use two climate change scenarios (A2 and B2) at two time periods in the EPIC agro-ecosystem simulation model. The applied climate change scenarios are from the HadCM3 global climate model for the periods 2015–2045 and 2070–2099 which projects consistent increases in temperature and precipitation of greater than 5°C and up to 300mm by 2099. An increase in the variability of temperature is also projected and is, accordingly, applied in the simulations. The EPIC model indicates that winter wheat yields would increase on average by 0.2Mgha−1 in the earlier period and by 0.8Mgha−1 in the later period due to warmer nighttime temperatures and higher precipitation. Simulated yields were not significantly affected by imposed changes in crop management. Simulated soil organic C content was higher under both NT management and double cropping than under CT continuous wheat. The simulated changes in management were a more important factor in SOC changes than the scenario of climate change. Soil C sequestration rates for continuous wheat systems were increased by an average of 0.4Mgha−1 year−1 by NT in the earlier period and by 0.2Mgha−1 year−1 in the later period. With wheat–corn double cropping, NT increased sequestration rates by 0.8 and 0.4Mgha−1 year−1 for the earlier and later periods, respectively. The total C offset due to a shift from CT to NT under continuous wheat over 16 million hectares in the Huang-Hai Plain is projected to reach 240TgC in the earlier period and 180TgC in the later period. Corresponding C offsets for wheat–corn cropping are 675–495TgC. [Copyright &y& Elsevier]

• A multi-objective assessment was conducted for alternative cropping systems in the NCP. • The dominant winter wheat-maize system had the largest ET, N leaching, and N 2 O emission. • Optimized winter wheat-maize system could perform best among the eight systems. • Conservation tillage could mitigate negative impacts of climate change and SOC decrease. • The study demonstrates a useful framework to develop climate smart agriculture systems. Developing climate-smart agricultural systems is essential for climate change adaptation and mitigation. In the past decades, the typical winter wheat- summer maize rotation system in the North China Plain (NCP) has produced high yield, but the overuse of nitrogen fertilizer and over-pumping of groundwater for irrigation have caused severe environmental problems. It is necessary to develop climate-smart agricultural systems through a comprehensive multiple-objective assessment and optimization of alternative cropping systems and agronomic managements. Here, with the agricultural system model of APSIM, eight alternative cropping systems at four typical sites across the NCP under two climate change scenarios and two tillage managements were comprehensively evaluated in terms of crop yield, water use efficiency (WUE), nitrogen use efficiency (NUE), evapotranspiration (ET), groundwater recharge (GWR), N 2 O emission, N leaching, surface soil organic carbon (SOC), and carbon footprint (CF). The results showed that under both baseline and future climate scenarios, the currently dominant winter wheat- summer maize rotation system had the largest ET, N leaching and N 2 O emission, a medium crop yield, WUE, and SOC, however a low NUE, and GWR. The rotation/intercropping systems could have higher grain yields, while the monoculture cropping systems could have advantage on water conservation. Maize had relatively higher yield, WUE, NUE, GWR, and SOC, and lower N loss and CF than wheat and soybean because it could have a high yield without irrigation. The optimized winter wheat-summer maize rotation system, with the optimal irrigation, fertilizer and cultivar, had the greatest advantage over other seven systems with the highest yields, WUE, NUE, high ET, GWR, and SOC, and the lowest N losses and CF. Compared with conventional tillage, each cropping system would have a little bit less negative response to future climate change with conservation tillage. The study demonstrated a useful framework to develop climate-smart agricultural systems and sustainable agricultural strategies to meet the challenges of global climate change, which can be widely applied to other cropping systems and regions. [ABSTRACT FROM AUTHOR]