Global food production faces a critical challenge: increasing yields while maintaining environmental sustainability. Conventional intensive farming, reliant on synthetic agrochemicals, has boosted yields but also led to significant greenhouse gas emissions and environmental degradation. This is particularly problematic in densely populated regions with limited agricultural resources, such as the North China Plain, where wheat-maize double cropping dominates and accounts for a substantial portion of China's cereal production. However, this system's reliance on synthetic fertilizers and its environmental impact are unsustainable. This six-year field study investigates the potential of diversified cropping systems, integrating cash crops and legumes into the conventional wheat-maize system, to address these challenges. The study aims to comprehensively assess the impact of diversified rotations on food production, greenhouse gas balance, soil health, and farmer income, testing hypotheses that cash-crop diversification increases farmer income without compromising yields, legume diversification reduces greenhouse gas emissions, and integrated diversified rotations increase food production, reduce emissions, and improve soil health. The North China Plain serves as a crucial case study due to its intensive cultivation and significant contribution to China's food security.

The literature highlights the need for sustainable intensification in agriculture to address the dual challenges of food security and environmental protection. Studies have shown the potential of integrated farming systems and diversified crop rotations to improve various agroecosystem functions, including increased yields and reduced environmental impacts. However, research on the combined effects of cash-crop and legume diversification on food production, greenhouse gas emissions, and soil health remains limited. Existing studies in North America, Europe, and Africa demonstrate the positive effects of crop diversification on yields, resilience to adverse weather, and reduced reliance on fertilizers, but findings from intensive food-producing regions like the North China Plain are needed to guide large-scale adoption.

A six-year (2016-2022) field experiment was conducted in the North China Plain at the Luancheng Agro-Ecosystem Station. The study utilized a randomized complete block design with six cropping systems: a control (winter wheat-summer maize), and five diversified rotations incorporating sweet potato, peanut, soybean, ryegrass-sweet sorghum, and spring maize. Each rotation was replicated three times. Various parameters were measured: * **Yields:** Plant biomass, grain yield (converted to wheat equivalents for comparison), protein yield, and farmer net income. * **Greenhouse gas emissions:** Soil N2O and CH4 fluxes were measured weekly using the static chamber method. Indirect GHG emissions from inputs were also calculated. Global warming potential (GWP) and net GHG emissions were determined. * **Soil health:** Soil physicochemical properties (pH, bulk density, soil water content, total nitrogen, dissolved organic carbon, nitrate-N, ammonium-N, available phosphorus, microbial biomass carbon, microbial biomass nitrogen) were measured at the beginning and end of the experiment. Soil organic carbon (SOC) was measured at different depths (0-90cm). Soil microbial community composition and diversity (Shannon index, Chao1, ACE, OTU richness) were analyzed using Illumina sequencing of 16S and ITS rRNA genes. The Cornell Soil Health Assessment (CSHA) method and principal component analysis (PCA) were used to evaluate overall soil health. * **Economic analysis:** Net income was calculated by subtracting production costs from the total revenue. Equivalent yields were calculated using market prices relative to wheat prices, adjusted for the Consumer Price Index (CPI). Statistical analyses included ANOVA, post-hoc LSD tests, correlation analysis, PCA, and redundancy analysis (RDA) to assess the relationships between different variables. A comprehensive evaluation index (CEI) was developed to assess the synergies and trade-offs among various indicators.

The key findings of this study are as follows: * **Increased productivity:** Diversified rotations, particularly those including sweet potato, significantly increased annual equivalent yields compared to the wheat-maize control (up to 38%). Sweet potato-wheat-maize rotation showed the highest increase in annual economic benefit (60%). The preceding crops positively affected the subsequent wheat-maize yields. * **Reduced greenhouse gas emissions:** Diversified rotations, especially those with legumes (peanut, soybean) and sweet potato, significantly reduced annual N2O emissions (by 30-49%) and increased CH4 uptake compared to the control. The GWP and net GHG emissions were significantly lower in diversified rotations (reduction of 75-92%). * **Enhanced soil health:** Legumes and sweet potato enhanced soil health. Peanut-wheat-maize rotation showed the highest soil health score, which was 41-59% higher than the control. SOC stocks increased in all treatments, with the highest increase observed in legume-based rotations. Microbial diversity (Shannon index, Chao1, ACE, OTU richness) significantly increased in rotations with legumes and sweet potato. * **Economic benefits:** Diversified rotations increased net income for farmers. Sweet potato-wheat-maize resulted in a 60% increase in net income compared to the control. Preceding diversified crops in rotation led to a 39-46% increase in economic benefit in the succeeding wheat-maize crops. These findings were statistically significant (*P* < 0.05 in most cases). The study also used a comprehensive evaluation index to integrate multiple aspects of system performance, demonstrating the superior performance of diversified systems.

The findings strongly support the hypotheses. Diversified crop rotations offer a substantial improvement over conventional wheat-maize monoculture in the North China Plain, demonstrating the feasibility of enhancing food production while mitigating environmental impacts and improving soil health. The reduction in N2O emissions is attributed to lower fertilizer use in legume-based systems and improved N use efficiency. The enhanced soil health, reflected in increased SOC, microbial diversity, and CSHA scores, is linked to the improved soil nutrient cycling and the diversity of root systems in the diversified rotations. The economic benefits highlight the potential for farmers to adopt these practices while increasing their income. These results align with previous studies showing the benefits of crop diversification in other regions, providing robust evidence for the scalability and adaptability of this sustainable agricultural approach.

This six-year field study provides compelling evidence for the substantial benefits of diversifying crop rotations in the North China Plain. Diversification significantly enhances food production, reduces GHG emissions, and improves soil health while increasing farmer income. The findings emphasize the importance of integrating cash crops and legumes into cropping systems for a more sustainable and resilient agriculture. Future research should focus on optimizing crop combinations for specific environmental conditions, exploring long-term impacts across multiple locations, and developing effective policies and incentives to encourage wider adoption of these practices.

The study was conducted at a single location in the North China Plain. While this site is representative of the region, the results may not be directly generalizable to other areas with differing climatic conditions or soil types. The six-year duration, while substantial, may not fully capture the long-term impacts of these rotations. Further research at multiple sites and over a longer time frame is needed to confirm the robustness of the findings and address potential inter-annual variability in weather patterns.