间套作是我国传统农业的精髓, 其存在2 000多年, 必然蕴含重要的科学原理。过去的研究表明其不仅能够大幅度提高作物产量, 而且能够充分利用地上部的光热资源, 充分挖掘和利用地下部水分养分资源, 强化农田生态系统服务功能。近年来, 国内外对其资源高效利用的研究取得了显著的进步, 特别是地下部资源高效利用方面。本文首先综述了相关研究的进展: 间套作作为增加农田生态系统生物多样性的重要措施, 具有重要的生态功能, 如提高作物产量, 增加作物生产力的稳定性, 充分利用地上部光热资源和土壤水分、土壤和肥料中的氮素和磷素以及微量元素等。随后, 对间套作提高资源利用效率的机制进行了分析, 包括水分需求上的时间和空间生态位互补, 豆科/禾本科间作体系中的豆科作物生物固氮和禾本科作物对土壤氮素利用上的互补和促进作用; 磷活化能力强弱搭配的间作体系中, 磷活化能力强的作物对活化能力弱的作物的促进作用; 双子叶和单子叶植物的搭配, 改善双子叶植物的Fe、Zn等微量元素的含量等。最后, 对间套作进一步研究方向和应用提出了一些看法和思路。在研究方面, 包括作物多样性与农业可持续发展, 地下部作物种间信号的传递, 地上地下部多样性的互反馈调节机制, 以及作物生长模型等。在应用方面, 包括豆科作物纳入农业生产体系发展生态集约化农业, 利用间套作发展有机农业, 利用种间相互作用提高磷肥利用率和增加作物可食部分的微量元素含量等。并认为间套作中的机械化、育种等问题的解决将有利于间套作的进一步发展。
Intercropping is one of the traditional farming systems practiced by farmers in China for more than 2 000 years with some intriguing ecological principles. Previous studies have shown that intercropping enhanced not only crop productivity, but also the utilization efficiencies of resources, including above-ground (e.g., land, thermal, radiation and space) and below-ground (e.g., water and nutrients) resources. Recent efforts have made some progresses on intercropping research. Here, we reviewed the potential of intercropping to strength ecosystem services and functions at the agroecosystem level, prospective research directions and highlight practical uses in modern agriculture. Intercropping increased biodiversity, productivity and stability of agroecosystems. At the same time, intercropping enhanced water use by isolating the time for maximum water requirements of one species from the other, and spatial complementarity by hydraulic lift of water. The enhancement of nitrogen acquisition was attributed to niche differentiation of N resources in which cereals acquired more mineral N from the soil, while legumes fixed more N from air N2. This was because that cereals was more competitive than legumes and mineral N competition increased symbiotic N2 fixation of legumes. Some P mobilized species facilitated the conversion of soil unavailable P into available P, which benefited not only the species but also the neighboring immobilized other species. E.g., the roots of faba bean released carboxylates or proton to dissolve sparingly soluble P in soils. Also the roots of chickpea released phytase or phosphatase to decompose organic P in the soil, which increased available soil P. There were interspecific facilitations of iron (Fe) and zinc (Zn) nutrients in intercropping of dicotyledonous or non-graminaceous monocotyledonous (strategy I for Fe acquisition and non-Fe or Zn mobilization) species and graminaceous monocotyledonous (strategy Ⅱ for Fe acquisition and Fe or Zn mobilization) species, which benefited micronutrient availability in intercropped non-Fe-mobilizing or Zn-mobilizing species. In the paper, I also identified some important future directions of intercropping research and practical uses. The research directions include crop diversity and agricultural sustainability, signal-controlled interspecific interactions between intercropped species, linkage interactions to above-ground and below-ground diversities, functional, structural and empirical models for intercropping, etc. In application, intercropping can be used to develop ecologically intensive agriculture and organic farming, to enhance fertilizer recovery, and to enrich the contents of microelements in edible parts of crops. Finally, it will be useful to further develop suitable machinery and breed newer crop varieties for intercropping.