Delineation of key areas of cultivated land quality improvement in Lulong County based on restriction degree

Cultivated land is not only an essential precondition for national food security, but also a material foundation for social security and sustainable development. The overall quantity of cultivated lands in China is large, but quality level has remained low. In order to design a definite direction for cultivated land consolidation and planning for different areas in Lulong County of Qinhuangdao, Hebei Province, this study established a quality evaluation indicator system for cultivated lands and determined the composite types of the limiting factors based on a score factor identification method. The study also introduced the obstacle degree model to modify the limiting factor combination used to delimit the key areas of cultivated land quality improvement. The results showed 15 981 plots of cultivated lands with high level limiting factors and 95 limiting factor combination types in Lulong County, which totally accounted for 43 909.71 hm² of cultivated croplands. After the introduction of an modified obstacle degree model, cultivated land of Lulong County was divided into 5 dominant limiting factor areas consisting of road accessibility dominated region, terrain slope dominated region, irrigation guaranteed dominated region, farmland shelter belt ratio dominated region and effective soil thickness dominated region. The biggest area (37 680.91 hm²) was mainly limited by farmland shelter belt ratio, accounting for 85.81% of the total cultivated area and mainly distributed across Lulong, Yanheying and Shuangwang Towns. The second-biggest area (3 861.32 hm²) was mainly limited by effective soil thickness, which was mainly distributed across Yinzhuang Town. The area limited mainly by road accessibility was 1 876.16 hm² and was mainly distributed across Shuangwang Town. The area limited mainly by probability irrigation was 319.44 hm², which was mainly distributed across Yanheying Town. The smallest area limited mainly by terrain slope was 171.87 hm², making up only 0.39% of the total cultivated area and mainly distributed across Liutiangezhuang Town. Based on the limiting factors in the main areas, the dominant limiting factors of cultivated land quality in Lulong County were farmland shelter belt ratio and effective soil thickness. Then probability irrigation and road accessibility played subsidiary roles in limiting cultivated land quality in the study area. The remediation processes of cultivated land included the strengthening of construction of shelter forest and the increase of effective soil thickness and improvement of soil fertility through enhancing farmland establishment and construction of feeder roads. The study provided technical support for planning consolidation strategies in hilly and mountainous areas and defining each section in the improvement of cultivated land quality. It also provided scientific basis for future farmland regulation in the region.