*4.1. Policy Implications for Utilization and Management of Multifunctional Cultivated Land*

Achieving the coordinated development of cultivated land for multiple functions is a long-term goal. In this study, we calculated and evaluated the values of each function of cultivated land and the multifunctional coupling coordination degree of cultivated land. Visualizing their spatial-temporal pattern can help us in understanding the evolution of the use of cultivated land for multiple functions. In addition, revealing the key driving factors behind the spatial-temporal evolution of the multifunctional coupling coordination degree of cultivated land can help us to clearly define the main factors influencing the coordinated development of various functions of cultivated land and allow us to put forward suitable and feasible development paths and plans for the orderly utilization of cultivated land for multiple functions. The policy implications are as follows:

Guaranteeing the comparative benefits of agricultural production and steadily increasing the level of disposable income of rural residents: The research results show that the disposable income level of rural residents is an important factor affecting the evolution of the multifunctional coupling coordination degree of cultivated land. Therefore, through policy regulation, the government should stabilize the price of agricultural production materials, increase the market price of grain crops, and raise the subsidy standard of grain cultivation to ensure the comparative benefits of agricultural production. By continuously improving the comparative income level of agriculture, steadily increasing the level of disposable income of rural residents, and continuously improving the economic and

production functions of arable land, the multifunctional utilization and management of cultivated land can be improved.

Enhancing the construction of agricultural production infrastructure to improve the level of agricultural development: According to the research results, the effective irrigation rate of cultivated land is an important factor affecting the development of the multifunctional coupling coordination of cultivated land. This shows that the construction of agricultural production infrastructure should be further improved in order to provide good production conditions for agriculture. Especially in the main grain-producing areas, agricultural production is the basis of all social and economic activities. It is therefore necessary to continuously improve the construction of agricultural infrastructure, create a good production environment for agricultural production, and effectively promote the coordinated development of multifunctional cultivated land based on the improvement of its production function.

Strictly implementing the farmland protection policy and continuously improving farmland productivity: Among the natural resource endowment conditions, the slope of cultivated land is a key factor affecting the evolution of the multifunctional coupling coordination degree of cultivated land. Slope represents the basic condition of cultivated land resources, and a suitable arable land slope is the foundation of agricultural production, ensuring a good grain yield, enriching the diversity of agricultural crops, and improving farmers' enthusiasm for farming. Therefore, the farmland protection policy must be strictly implemented and the use of farmland with suitable slopes for non-food and nonagricultural production must be strictly prohibited. Through the implementation of policies and measures such as "storing grain in the land" and "storing grain in technology" to protect the cultivated land effectively, we can improve the quality of cultivated land and the production capacity of cultivated land. The coordinated development of multifunctional cultivated land is promoted through the synergistic improvement of the production, social, and ecological functions of cultivated land.

#### *4.2. Contribution to Research, Limitations, and Future Perspectives*

During the rapid process of rural development, ensuring the success of multifunctional cultivated land in China has become a critical objective in achieving the sustainable use of cultivated land. The existing studies in this area have provided us a cultivated land multifunction utilization level through the improved TOPSIS model [3], but the results of empirical analysis can only tell us the distance from the current utilization level to the optimal utilization level of multifunctional cultivated land. This does not allow us to clearly evaluate the actual use of multifunctional cultivated land. Thus, in this study we combined the Comprehensive Index Model and the Coupling Coordination Degree Model to calculate the exact coupling coordination degree of multifunctional cultivated land, which provided much clearer results relating to the multiple functions of cultivated land. Furthermore, the existing studies in this area mostly focus on the factors influencing cultivated land use [26,38,45]. However, cultivated land is a complex system and the interaction of different factors can have an impact on multifunctional cultivated land. Detailed analyses of cultivated land used for multiple functions and the impact of its interaction are rare. Thus, we used Geodetector to explore the effect of the interaction of multiple factors on the multifunctional coupling coordination degree of cultivated land, providing a deeper understanding of the spatial-temporal patterns and driving forces behind the use of cultivated land for multiple functions.

However, in this study we only considered the production, social, and ecological functions of cultivated land, ignoring other factors such as landscape functions, cultural functions, reserve functions, etc. In a future follow-up study, our analysis of the use of cultivated land for multiple functions will be further extended to allow for the establishment of an index system for the evaluation of multifunctional cultivated land. This will be supplemented with microdata to allow us to further analyze the spatial distribution of the multifunctional coupling coordination degree of cultivated land, to explore the trend of the spatial-temporal evolution of the multifunctional coupling coordination degree of cultivated land more scientifically, and to provide scientific reference for the management and utilization of multifunctional cultivated land.

#### **5. Conclusions**

In this paper, we analyzed the production, social, and ecological functions as well as the spatial-temporal evolution of the multifunctional coupling coordination degree of cultivated land in major grain-producing areas of northeast China in 2005, 2010, 2015, and 2020, revealing the driving forces. The research showed that:

From 2005 to 2020, the production, social, and ecological functions of cultivated land in the study areas showed significant regional differences, and the multifunctional coupling coordination degree of cultivated land in the study areas showed a trend of gradual improvement, but did not reach a level of good coordination. As time passed, the number of cities (districts) in the study areas where the degree of multifunctional coupling coordination of cultivated land was seriously out of balance remained unchanged.

As for the driving forces, the spatial-temporal evolution of the multifunctional coupling coordination degree of cultivated land in the study areas was mainly influenced by the level of agricultural development. According to the results obtained from the analysis of the factor detection module of Geographical Detector, the level of per capita disposable income in rural areas and the effective irrigation rate of cultivated land representing the level of agricultural development were ranked highest in almost every year, showing a strong explanatory power for the spatial-temporal pattern of the multifunctional coupling coordination degree of cultivated land. In addition, the slope factor in the natural resource endowment category and the urbanization factor in the socioeconomic category also exerted an important influence on the spatial-temporal pattern of the multifunctional coupling coordination degree of cultivated land in the study areas.

**Author Contributions:** J.G. is responsible for conceptualization, formal analysis, writing—original draft preparation, and writing—review and editing. Y.Z. is responsible for methodology. R.Z. is responsible for writing—review and editing. H.S. is responsible for visualization. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by Ministry of Education Humanities and Social Sciences Foundation Youth Project of China, Grant Number: 19YJC630037; National Natural Science Foundation of China, Grant Number: 42101254; Fundamental Research Funds for the Central Universities, Grant Number: N2114002; Soft Science Research Project of Liaoning Province, Grant Number: 2021JH4/10100065.

**Data Availability Statement:** The data presented in this study are available in the article.

**Conflicts of Interest:** The authors declare no conflict of interest.
