In China, the traditional early and late season double rice (DR) system is declining accompanied by the fast increase of two newly developed cropping systems: ratoon rice (RR) and rice–crawfish (RC).  Three methodologies: economic analysis, emergy evaluation and life cycle assessment (LCA) were employed to evaluate the economics and sustainability of this paddy cropping system change.  Economic analysis indicated that the income and profit of the RC system were far larger than those of RR and DR.  The income to costs ratio of RR and RC increased by 25.5 and 122.7% compared with that of DR, respectively.  RC had the highest emergy input thanks to increasing irrigation water, electricity, juvenile crawfish and forage input while RR showed a lower total emergy and nonrenewable emergy input, such as irrigation water, electricity, fertilizers and pesticides than DR.  The environmental loading ratios decreased by 16.7–50.4% when cropping system changed from DR to RR or from DR to RC while the emergy sustainability indexes increased by 22.6–112.9%.  The life cycle assessment indicated lower potential environmental impacts of RR and RC, whose total environmental impact indexes were 35.0–61.0% lower than that of DR.  Grain yield of RR was comparable with that of DR in spite of less financial and emergy input of RR, but RC had a much lower grain yield (a 53.6% reduction compared to DR).  These results suggested that RR is a suitable cropping system to achieve the food security, economic and environmental goals.

      Annual ryegrass (Lolium multiflorum Lam.), a non-leguminous winter cover crop, has been adopted to absorb soil native N to minimize N loss from an intensive double rice cropping system in southern China, but a little is known about its effects on rice grain yield and rice N use efficiency. In this study, effects of ryegrass on double rice yield, N uptake and use efficiency were measured under different fertilizer N rates. A 3-year (2009–2011) field experiment arranged in a split-plot design was undertaken. Main plots were ryegrass (RG) as a winter cover crop and winter fallow (WF) without weed. Subplots were three N treatments for each rice season: 0 (N₀), 100 (N₁₀₀) and 200 kg N ha^–1 (N₂₀₀). In the 3-year experiment, RG reduced grain yield and plant N uptake for early rice (0.4–1.7 t ha^–1 for grain yield and 4.6–20.3 kg ha^–1 for N uptake) and double rice (0.6–2.0 t ha^–1 for grain yield and 6.3–27.0 kg ha^–1 for N uptake) when compared with WF among different N rates. Yield and N uptake decrease due to RG was smaller in N₁₀₀ and N₂₀₀ plots than in N₀ plots. The reduction in early rice grain yield in RG plots was associated with decrease number of panicles. Agronomic N use efficiency and fertilizer N recovery efficiency were higher in RG plots than winter fallow for early rice and double rice among different N rates and experimental years. RG tended to have little effect on grain yield, N uptake, agronomic N use efficiency, and fertilizer N recovery efficiency in the late rice season. These results suggest that ryegrass may reduce grain yield while it improves rice N use efficiency in a double rice cropping system.