耕地复种指数研究的关键科学问题

在当前耕地外延式扩展难以满足、粮食单产提升难度加大的新形势下，提升耕地复种指数、走耕地内涵式集约利用模式，是确保未来我国粮食增产和国家粮食安全的重要途径。本文从农业土地系统科学视角出发，系统总结了耕地复种指数研究的总体研究框架和核心研究内容，全面梳理了国内外该领域的研究现状、进展及存在的问题。研究认为，第一，格局与过程探测是耕地复种指数研究的重要基础。不仅要关注耕地潜在或实际复种指数的数量、空间分布、区域差异及其时空变化过程，更要关注耕地复种指数的提升空间，科学描述可挖掘的复种潜力。第二，功能与效应分析是耕地复种指数研究的核心内容。现有研究多聚焦耕地复种指数提升对粮食产量增加的贡献作用，复种指数变化的生态环境效应研究以微观试验性研究为主；迫切需要建立综合效应分析框架，从不同的学科、视角和尺度揭示耕地复种指数对区域资源配置、社会经济和生态环境等的影响和反馈机制。第三，优化调控是耕地复种指数研究的关键任务。科学提出可持续挖掘和提升耕地复种潜力的策略，重点强化可持续性评估、障碍性因子分析和系统性优化调控等方面的研究，追求粮食安全、资源安全和生态安全的权衡协调，以建立人地和谐、可持续的农业土地利用模式。耕地复种本质上反映了复杂的“人-地”耦合关系，多数据、多尺度、多模型和多方法的综合研究将是未来耕地复种指数研究的重要发展方向，将会促进自然科学、工程科学和社会科学等多个学科门类的综合、交叉和集成研究。

Key Research Priorities for Multiple Cropping Systems

To feed the China’s growing population, more food needs to be produced using currently available cropland. Further expansion of cropland seems to be unlikely as it largely conflicts with biodiversity conservation, greenhouse gas emission mitigations, and hydrological changes. Crop yield growth is also confronting with large challenges as it becomes more difficult to sustain further yield increase as farmers’ yields approach the potential threshold. Increasing cropping intensity may thus provide another promising opportunity to increase food production. An increase in cropping intensity by increasing the number of crops per cropping cycle or intercropping with other crops can increase the frequency of harvests each year, resulting in increased food supplies without additional cropland expansion. This paper, from the perspective of agricultural land systems, proposed the overall study framework of multiple cropping systems and provided an overview of current research progresses in the three key research priorities. It was indicated that: (1) Multi-faceted patterns and processes of multiple cropping systems were the basis for subsequent analysis. It should consider not only the quantity, spatial distribution, regional difference of potential or actual multiple cropping systems, but also the cropping intensity gaps so as to expand the harvest areas by closing these gaps. (2) Understanding of the effects of multiple cropping systems on socio-economic and biophysical systems was the core task. Currently, most of studies were focused on the positive contribution of multiple cropping systems to food production, and less attention was paid to its impacts on eco-environment. Interdisciplinary approaches and cross-scale integration are critically necessary for better understanding the complex effects and feedbacks of multiple cropping systems on regional resource allocation, socio-economic development and eco-environment health. (3) How to sustainably increase the multiple cropping indexes was facing great challenges. It was important to link the multiple cropping systems with other parallel systems to understand their synergies and trade-offs, in order to build up a sustainable pathway for increasing future cropping intensity. All these solutions would substantially promote the interdisciplinary integration and would contribute to better understand the coupled human-environment interactions across time, space and scales.