In 2021, China achieved a comprehensive victory in the battle against poverty, and fully advancing the work of rural revitalization became the new focus of efforts. As an important component of rural areas, cultivated land is the material foundation and important support for rural revitalization.The multifunctional evaluation of cultivated land can help to reveal the multifunctional value of cultivated land, providing more reasonable cultivated land use and optimization measures by exploring the key areas and types of trade-offs and synergy between functions. It is of great significance for advancing the rural revitalization strategy and achieving the modernization of agriculture and rural areas. Taking Hebei Province as the research area, this paper constructs a functional evaluation index system to classify and evaluate cultivated land's production, ecological and living functions and subfunctions. Based on Spearman rank correlation and spatial autocorrelation, we examined the trade-offs and synergy among different cultivated land functions, used the natural discontinuity classification method to divide cultivated land functions into secondary, tertiary and fourth-level classifications, compared the Spearman rank correlation coefficients between the functions in each group of data, determined regional differences in functional correlation, identified key functional trade-off and synergy regions as well as sub-functional role types, and finally cultivated land functional zones and core areas were divided. The results show that: (1) From 2010 to 2020, the production function of cultivated land in Hebei Province remained stable, the ecological function decreased, and the living function gradually improved. The three functions are all in a synergy relationship and apart from a weakening in the synergy between living and ecological functions from 2015 to 2020, the degree of synergy among other types of functions has gradually increased. (2) The key areas for functional synergy are mostly high-value areas. In the zoning based on the level of production function, the relationship between production function and ecological function shifted from low-value synergy to high-value trade-off. And in the zoning based on the level of living function, the synergy between the living function and the other two types of functions decreased as the living function improved. (3) There are more complex trade-offs and synergy among the subfunctions of cultivated land in Hebei Province. The synergy between landscape aesthetic subfunction and the three types of production subfunctions is the key to the synergy between production function and ecological function, and the synergy between landscape aesthetic subfunction and food security subfunction contributes the most to the synergistic relationship between ecological function and living function, and the synergy between grain production subfunction, large-scale production subfunction and food security subfunction is the key synergy between production function and living function. (4) Based on the values of cultivated land function, 6 types of cultivated land function advantage areas are divided, and 3 types of core functional areas are identified by combining spatial autocorrelation analysis. Our research analyzes the regional differences in trade-offs and synergy of cultivated land functions, identifies the important types of subfunctions that make significant contributions to functional synergy and divides cultivated land functional zones accordingly, to provide a more accurate optimization scheme for cultivated land use.

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.

The spatial distribution of soil organic carbon (SOC) and its influencing factors are very crucial to the soil properties and sustainable land use. Among them, the hilly area of eastern Sichuan is dominated in the food security and ecological protection. However, some agricultural practices (such as over-cultivation and excessive use of fertilizers) have led to the decline in the SOC content. There are the increasing risks on the soil health and the long-term sustainable agriculture. This study aims to explore the SOC distribution in the hilly areas of eastern Sichuan, according to the unique terrain and soil texture characteristics. 1 301 soil samples were collected from five fields in the various districts and counties, indicating the representative coverage of all secondary cultivated land categories. The soil samples were taken at a depth of 15–30 cm with the distribution of organic carbon in agricultural soils. A systematic analysis was implemented on the influencing factors on SOC content. Two categories were classified into: external environmental random and soil endowment factors. External environmental factors included the meteorological data, such as annual mean temperature and precipitation. While the soil endowment factors were encompassed the physicochemical inherent properties of the soil, including texture, parent material, and nutrient content characteristics. Topographical data (such as slope and elevation) was derived from DEM (Digital Elevation Model) calculations, in order to explore the impact of terrain on the SOC distribution. A combination of statistical methods, spatial analysis, and random forest models was employed to assess the correlation between these influencing factors and the SOC distribution. Results indicate that: 1) SOC content was ranged from 4.91 to 15.26 g/kg in the hilly areas of eastern Sichuan, with an average of 7.39 g/kg and a coefficient of variation of 21.70%. It infers that there was the moderate spatial variability across the region. 2) The Gaussian model revealed a nugget effect of 0.173, with a nugget ratio of 61.5%, indicating the moderate spatial variation at small scales. 3) The Kriging interpolation was used to predict a spatial pattern of SOC distribution. A "north high, south low" trend was found with the SOC levels gradually increasing from the southern to northern regions. This spatial variation was attributed to the external environmental random factors and soil endowment factors. 4) Climate and topography shared the significant correlations with the SOC content (P < 0.01). Among them, annual mean temperature displayed a strong negative correlation (−0.72) with the SOC content, while the correlations with precipitation (0.34) and slope (0.30) were relatively weak. 5) Soil texture and physicochemical properties were the most significant influencing factors on the SOC content, overshadowing the influence of topographical and climatic conditions. The findings were emphasized that the soil management practices (particularly on the soil texture and nutrient levels) shared the greatest impact on the SOC distribution. 6) The various models were tested. Among them, the random forest regression model performed the best to predict the SOC distribution. Therefore, the nutrient content was identified as the most critical influencing factor on SOC, accounting for 61.3% of the spatial variation. In contrast, topographical factors were contributed only 1.7%, indicating the relatively minor role of terrain in determining SOC levels. These findings suggest that the soil nutrient management can be expected to enhance the SOC content in the sustainable agricultural practices in the hilly areas of eastern Sichuan. This finding can provide the promising insights for the influencing factors on SOC distribution. The importance of targeted land management was highlighted to enhance the soil health for the sustainable agricultural productivity.