Chinese milk vetch (Astragalus sinicus L., vetch), a leguminous winter cover crop, has been widely adopted by farmers in southern China to boost yield of the succeeding rice crop. However, the effects of vetch on rice grain yield and nitrogen (N) use efficiency have not yet been well studied in the intensive double-cropped rice cropping systems. To fill this gap, we conducted a three-year field experiment to evaluate the impacts of the vetch crop on yields and N use efficiency in the subsequent early and late rice seasons. With moderate N input (100 kg N ha⁻¹ for each rice crop), vetch cover significantly increased grain yields by 7.3–13.4% for early rice, by 8.2–10.4% for late rice, and by 8.6–11.5% for total annual rice production when compared with winter fallow. When rice crops received an N input of 200 kg N ha⁻¹, vetch cover increased grain yields by 5.9–18.4% for early rice, by 3.8–10.1% for late rice, and by 6.2–11.3% for annual rice production. Moreover, comparable grain yields (11.9 vs. 12.0 Mg ha⁻¹ for annual rice production) were observed between vetch cover with moderate N and fallow with added N fertilizer. Yield components analysis indicated that the increased tillering number was the main factor for the enhanced grain yields by vetch cover. Vetch cover with moderate and higher N input resulted in higher agronomic N use efficiency and applied N recovery efficiency compared with the fallow treatments. Here, our results showed that vetch as a winter cover crop can be combined with reduced N fertilizer input while maintaining high grain yields, thus gaining a more sustainable rice production system.

The use of oilseed rape (OS, Brassica napus L.) as a winter green manure is crucial for enhancing soil fertility and reducing chemical N application in paddy fields. However, the impacts of replacing varying amounts of chemical N with OS on CH₄ and N₂O emissions in paddy soils have not been well evaluated. In this study, GHG emissions, soil properties and OS decomposition in a rice-ratooning system with different OS-urea N replacement rates (0%, 25%, 50%, 75% and 100%) were investigated. Our results indicate that 84.7–90.7% of the initial C and 97.5–98.4% of the N were released during the 192-day decomposition process, and that the mineralization patterns of net C and net N in the OS residue were consistent with a single exponential decay model. The lowest CH₄ emissions (9.97 g m⁻²) were observed at 0% OS, while the highest N₂O emissions (0.40 g m⁻²) were observed at this level of substitution. Conversely, the highest CH₄ emissions (20.71 g m⁻²) and lowest N₂O emissions (0.07 g m⁻²) were observed at 100% OS. Compared to 0% substitution, 25% substitution significantly decreased GWP and GHGI without reducing rice grain yield. Environmental parameters such as soil redox, NH₄⁺-N and residual N and C were shown to be significantly associated with CH₄ emissions, whereas soil redox, NH₄⁺-N and residual C were the main drivers of N₂O emissions. In conclusion, 25% substitution of OS was the most cost-effective measure for balancing greenhouse gas emission and rice yield.

Ratoon rice is a planting system that efficiently utilizes temperature and light resources. However, multiple fertilization applications are typically required to maintain stable rice yields. Improper fertilization not only poses challenges to scarce labor resources but also increases carbon footprints (CFs). Research on the effects of different fertilization strategies on greenhouse gas (GHG) emissions, yield, CF, and ecosystem net economic benefits (NEEBs) in ratoon rice systems remains limited. A two-year field experiment was conducted to evaluate the effects of one conventional fertilization strategy and four optimized fertilization strategies on GHG emissions, yield, CF, and NEEBs in the ratoon rice system. The conventional fertilization strategy applied urea in five splits (FFP, 280 kg N·ha⁻¹). The optimized strategies included (1) one-time side deep application controlled-release fertilizer (CRF, 280 kg N·ha⁻¹); (2) CRF with 20% N replaced by organic fertilizer (OF + CRF1); (3) the same as (2) with a 10% N reduction (OF + CRF2, 252 kg N·ha⁻¹); and (4) the same as (2) with a 20% N reduction (OF + CRF3, 224 kg N·ha⁻¹). The results showed that compared with FFP, optimized fertilization treatments reduced CH₄ and N₂O emissions by 28.69% to 55.27% and 25.08% to 40.32%, respectively. They also increased the annual rice yields by 2.22% to 19.52% (except OF + CRF3). Optimizing fertilization treatments reduced annual CF, CF_Y, and CF_EC by 26.66% to 49.59%, 34.11% to 51.12%, and 25.35% to 41.47%, respectively. These treatments also increased NEEBs by 8.27% to 34.23%. Among them, OF + CRF1 and OF + CRF2 treatments achieved the highest NEEB. In summary, CRF treatments can balance ratoon rice yield and environmental benefits. Replacing part of the N with organic fertilizer further enhances annual yield and NEEBs.

Rising temperatures, extreme precipitation events such as excessive or insufficient rainfall, increasing levels of carbon dioxide, and associated climatic factors will persistently impact crop growth and agricultural production. The warming temperatures have reduced the agricultural crop yields. Rice (Oryza sativa L.) is the major food crop, which is particularly susceptible to the effects of climate change. It is very important to accurately evaluate the impacts of climate change on rice growth and rice yield. In this study, the rice growth during 1981–2018 (baseline period) and 2041–2100 (future period) were separately simulated and compared within the CERES-Rice model (v4.6) using high-quality weather data, soil, and field experimental data at six agro-meteorological stations in Hainan Province. For the climate data of the future period, the SSP1-2.6, SSP3-7.0, and SSP5-8.5 scenarios were applied, with carbon dioxide (CO₂) fertilization effects considered. The adaptation strategies such as adjusting planting dates and switching rice cultivars were also assessed. The simulation results indicated that the early rice yields in the 2050s, 2070s, and 2090s were projected to decrease by 6.2%, 11.8%, and 20.0% when the CO₂ fertilization effect was not considered, compared with the results of the baseline period, respectively, while late rice yields would decline by 9.9%, 23.4%, and 36.3% correspondingly. When accounting for the CO₂ fertilization effect, the yields of early rice and late rice in the 2090s increased 16.9% and 6.2%, respectively. Regarding adaptation measures, adjusting planting dates and switching rice cultivars could increase early rice yields by 22.7% and 43.3%, respectively, while increasing late rice yields by 20.2% and 34.2% correspondingly. This study holds substantial scientific importance for elucidating the mechanistic pathways through which climate change influences rice productivity in tropical agro-ecosystems, and provides a critical foundation for formulating evidence-based adaptation strategies to mitigate climate-related risks in a timely manner. Cultivar substitution and temporal shifts in planting dates constituted two adaptation strategies for attenuating the adverse impacts of anthropogenic climate change on rice.

Ratoon rice monoculture system (RR) is a labor-efficient and high-yielding cropping system in southern China. The rice–duck coculture system has been increasingly recognized as a mutually beneficial agricultural practice. However, the environmental impacts, economic performance, and sustainability of transitioning from a RR monoculture to a ratoon rice–duck system (RR-D) coculture remain unclear. A three-year (2022–2024) field experiment with three replications was therefore conducted in the Jianghan Plain, China (29°41′ N, 112°25′ E), to compare greenhouse gas (GHG) emissions, economic benefits, and emergy-based sustainability indicators between the RR and RR-D systems at a significant level of p < 0.05. The results showed that the RR-D significantly reduced CH₄ emissions by 25.7–39.5% but increased N₂O emissions by 18.7–122.2%. The average global warming potential (GWP) and GHG intensity decreased by 27.8% and 30.7%, respectively. Meanwhile, RR-D increased economic benefits by 131.0–167.1%, but lowered the unit emergy value per economic benefit (UEV_Benefits), renewable emergy ratio (%R), emergy yield ratio (EYR), and emergy sustainability index (ESI), and increased the environmental loading ratio (ELR). Overall, RR-D may improve economic returns and GHG mitigation, but its emergy-based sustainability requires optimization of feed, labor, and duck stocking density.