Abstract:Marginal land refers to the land with low agricultural productivity and economic benefit and fragile ecology due to the prominent limitation of soil barrier, strong restriction of water and heat resources as well as harsh topographic conditions. In China, the existing marginal land is about 1.17 billion mu (15 mu is equal to 1 ha), which is the most important resource of strategic emergency to deal with the cultivated land gap of 700 million mu. Marginal land storage is a major strategy for national food security. It has become a new international research trend to increase the productivity and ecological functions of marginal land by modulating the interaction between plant and soil microbial. This includes breeding high stress-tolerant plants, screening and application of plant growth promotion rhizobacteria (PGPR) to promote plant growth on marginal land, and strengthening soil microbial functions to improve soil quality and health. In view of the marginal land productivity expansion and ecological benefit improvement, it is necessary to formulate the overall action plans based on the principles of ecological priority and green development. We should carry out the marginal land R & D project with the idea of "plant first, soil-improvement as the base, water security, microbial control, and the integration of plant-soil-microbial ecological system". (1) We should build a national database of marginal land and formulate the protection and management zoning plan. (2) We should develop four aspects of basic theory research namely, stress-tolerant plants breeding and its adaptive mechanism, efficient utilization of water and fertilize, soil obstacle factor reduction and biological networks induction/acclimatization, and the interaction between plant and microbial. (3) Focusing on coastal saline-alkali land in north and east China, soda alkali-saline land in northeast China, saline-alkali land in northwest inland, yellow spongy soils slope on the loess plateau, red soil and purple soil slope land in south hilly region, we should build different types of ecological farmland by integrating various technologies and theories. This will promote the protection and sustainable utilization of marginal land resources, and support the timely launch of the efficient use of contiguous marginal land to achieve the goal of increasing productivity by adding 700 million mu of medium-high grade arable land. This will be also helpful to ensure the implementation of the strategy of "storing grain in land and technology" and rural vitalization, and the construction of ecological civilization in China's ecologically fragile areas.