Development history, present situation, and the prospect of subsurface drainage technology in China

Subsurface drainage technology is important for the improvement of saline-alkali land, the drainage of waterlogged areas, and the nutrient management in rice fields. In the first 20 years of this century, subsurface drainage technology developed rapidly; thus, a review of its development history and the present situation will provide a comprehensive understanding of this technology and highlight its future development. Data were obtained from the China National Knowledge Infrastructure (CNKI), Wanfang, Weipu, Baidu Academic, and Elsevier and the National Natural Science Foundation of China and Baidu Search. Statistical analysis was used to analyze the development trends, use changes, spatial distribution of application, application area, and service objects of subsurface drainage technology. The results showed that for the past 50 years, the development of China's subsurface drainage technology was divided into a preliminary exploration period (1976-1998), a gradual development period (1999-2008), and a vigorous development period (2009-2020). Jiangsu and Shandong Provinces were areas of intense research on subsurface drainage technology, and rice, wheat, corn, and cotton were the main service objects of subsurface drainage engineering in China. For saline-alkali land improvement, subsurface drainage techniques had developed rapidly, mainly for leaching soil salt. The integration of water and salt control technology and the ecological restoration of subsurface drainage represented an important direction for future development of subsurface drainage technology. With the renewal of subsurface drainage, new filter materials, and improvements to the intelligent laying efficiency of subsurface drainage construction machinery, the application of subsurface drainage technology will be more extensive.