Abstract :
[en] As a natural climate solution, soil organic carbon (SOC) sequestration in agroecosystem contributes to the achievement of global climate goals. Paddy soils store a huge amount of SOC and play a pivotal role in providing ecosystem services (e.g. climate change mitigation and food security). Exploring the magnitude of SOC sequestration in paddies as well as its benefits on crop production is vital for developing strategies to mitigate climate change and ensure food security. Climate change poses a great threat to global food security, and developing climate change mitigation strategies is imperative to improve the sustainability and resiliency of agriculture.
In this study, a dataset from seven long-term field experiments (since 1980s/1990s) in paddies in the Yangtze River Basin was established. We explored the characteristics of SOC sequestration and crop yield as well as their driving factors under different fertilisation treatments (CK: no fertiliser application, NPK: application of chemical nitrogen, phosphorus and potassium fertilisers, M: application of manure; NPKM: a combination of NPK and M) in two rice-based cropping systems (R–W: middle rice–winter wheat system, R–R: early rice–late rice system). The sustainable yield index (SYI) and the coefficient of variation (CV) were used to quantify yield sustainability and stability. Random forest (RF) and structural equation modelling (SEM) were conducted to quantify the relative importance of different driving factors and their direct and indirect effects on SOC sequestration and yield. To identify climate change feedback and propose climate change mitigation strategies in the future (2024–2100), we calibrated and validated the process-based model SPACSYS with dataset from long-term (>30 years) field experiment in R–W system in Southwest China. Two future climate change scenarios (SSP1–2.6 and SSP5–8.5) and baseline scenario and three mitigation management scenarios including reduced N application rate by 20 % (RNA), the introduction of mid-season drainage (MSD) and integrated management combining RNA with MSD (IM) were conducted. The main results are as follows:
(1). The topsoil SOC stock (0–20 cm) significantly increased by 8.6 t ha–1 on average under NPKM treatment in R–W system and by 2.5–6.4 t ha–1 on average under NPK and NPKM treatments in R–R system compared with CK treatment during the last four decades. A higher SOC sequestration rate and a longer SOC sequestration duration were found in NPKM treatment than that in NPK treatment in both systems. The fertilisation-induced increases of the SOC stock in the R–W system (NPK: 15.5 %, NPKM: 31.5 %) were higher than that in the R–R system (NPK: 7.4 %, NPKM: 21.6 %). The SEM analysis indicates that soil properties, especially initial SOC content, determine the difference in SOC sequestration between the two systems.
(2). The NPKM treatment produced the highest grain yields for both rice and wheat in the two systems, followed by NPK/M and CK treatments. The NPK and NPKM treatments generally had higher SYI (0.34–0.74) and lower CV (11–32 %) than the M and CK treatments (SYI: 0.29–0.62 and CV: 15–44 %). Crop grain yields were significantly increased with increasing SOC stock (0–20 cm) and followed a logarithmic regression in both systems. SEM analysis revealed that SOC had indirect (through improvements in soil properties) positive impacts on crop yields in the R–R system.
(3). The SPACSYS model performed effectively in simulating yield and nitrogen content in grain and straw, SOC stock and methane (CH4) and nitrous oxide (N2O) emissions in R–W system. Compared to the baseline scenario, the climate under the SSP1–2.6 scenario considering the carbon dioxide (CO2) fertilisation effects may benefit wheat yield (28 %) and had no effects on rice yield. In contrast, under SSP5–8.5 scenario, whether CO2 fertilisation effects are considered or not, both rice and wheat yield could face great loss (i.e., 11.8–29.9 % for rice, 8.3–19.4 % for wheat). The winter wheat would not be suitable for planting in the distant future (2070–2100) due to the incomplete vernalisation caused by warming. The switching from winter wheat to spring wheat from 2070 onward could totally avoid the yield loss. Under SSP1–2.6 and SSP5–8.5 scenarios, the SOC sequestration rate (0–20 cm) could decrease, the IM scenarios could significantly reduce CH4 emissions by 55 % and 57 % and N2O emissions by 23 %, as such reducing the net global warming potential by 69 % compared to no adaptation.
In conclusion, our study reveals that manure amendment on the basis of chemical fertilisation is beneficial for both SOC sequestration and crop production in paddies. There is a synergy between SOC stock and crop production. In future, crop substitution combined with integrated management can achieve the synergy between global warming mitigation and food security services from rice paddies in Southwest China. Our study provides insights into sustainable agricultural management for food security and ecosystem services in paddies.
