Provincial fallow scale and fallow spatial layout of cultivated land in China from the "Trinity" protection perspective

Fallow land can often be implemented under the pattern of cultivated land protection on quantity, quality, and ecology in the strategy of "Storing Grain in Land" in China. The spatial arrangement of fallow land is closely linked to the fallow land implementation and the nationwide allocation of arable land resources. However, the current macro research has hindered to determine the optimal spatial layout of fallow land nationwide in sustainable agriculture at present. The purpose of this study is to explore the maximum scale and spatial layout of provincial fallow in China under the constraint of food security. The primary research subjects were selected as the provinces of China that were excluded from Hong Kong, Macao, and Taiwan. The data was derived from the publicly accessible statistical yearbooks from 2000-2019. Firstly, a numerical model was developed to calculate the fallow land scale under food security guidelines, according to the arable land retention. System dynamics, grey model, time series analysis, and exponential decay model were utilized to scientifically predict the fallow scale in China in the future. Secondly, an evaluation system was established for the urgency of fallowing arable land in Chinese provinces using the Pressure-State-Response (PSR) model, according to the land quality and ecological security. The evaluation index system was comprised of 17 specific indicators. Finally, the fallow scale of each province was allocated to determine the different fallow zones after evaluation. Therefore, a provincial space layout of fallow was established using the "Trinity" protection of quantity, quality, and ecology. The results show that: (1) The maximum fallow scale was expected to be 3 237.310×10⁴, 2 678.970×10⁴, and 2 120.640×10⁴ hectares by 2030 under 90%, 95%, and 100% grain self-sufficiency rates, respectively. At the same time, it was particularly crucial to reasonably and scientifically calculate the fallow land scale. A comprehensive fallow land system was established to promote nationwide; (2) Provincial urgency assessments show that Shanghai and Inner Mongolia were ranked the highest in the urgency for the fallow land, while Sichuan and Guangxi were ranked the lowest. Strategic allocation of fallow land was prioritized for the regions with the higher levels of urgency; (3) The scale and urgency were combined to assess the fallow land. The maximum scale of fallow land was calculated to be 15.55036 million hectares in 2019, while it was projected to be 20.87778 million hectares by 2030. The areas of each province were categorized into five levels of fallow land. There were significant regional differences in the fallow land scale. Inner Mongolia and Gansu shared the larger scales, compared with Beijing and Shanghai with the smaller ones. This finding can provide the theoretical references and technical support to establish the differentiated fallow system. Some ideas can also be offered to fully establish and effectively implement the fallow system in the future, thus integrating quantitative, qualitative, and ecological multiple objectives into the spatial zoning of fallow land.