4.2.2. Local Spatial Autocorrelation Analysis

The LISA agglomeration shows the spatiotemporal evolution characteristics of the agglomeration of the CLUT (Figure 9). From 2001 to 2019, the high-high agglomerations of the comprehensive transition of cultivated land use were concentrated in the northeast and southwest of the region, the high-high agglomerations of the spatial transition were concentrated in the northeast, and the high-high agglomerations of the functional transition were distributed in the southwest. This is mainly affected by the differences in location, national policies, and economic development stages, which are analyzed in Sections 4.1.2 and 4.1.3 of this study. The low-low agglomerations of the cultivated land-use comprehensive, spatial, and functional transitions were distributed in the central region. Combined with Figure 2, it is found that most of these areas are in the transitional zone from mountainous and hilly to plains, with low economic development levels and poor agricultural production techniques. There are few contiguous and flat cultivated lands that are convenient for cultivation, and fragmentation is serious. Thus, the optimization of the cultivated land spatial and functional morphology is restricted to a certain extent.

**Figure 9.** Local spatial correlation map of CLUT. **Figure 9.** Local spatial correlation map of CLUT.

#### *4.3. Changes in the Gravity Center of the CLUT 4.3. Changes in the Gravity Center of the CLUT*

Figure 10 shows that the overall direction of the gravity center of the comprehensive transition moved from the southwest to the northeast from 2001 to 2019. The migration direction of the gravity center of the spatial transition is basically the same as that of the comprehensive transition, while the functional center of gravity moves in the opposite direction from northeast to southwest. However, since 2013, the movement direction of the gravity center of the spatial transition and functional transition has converged, and the distance between the centers of gravity has been reduced, which is due to the narrowing of the economic level gap within the region. The development of society is a staged process. Therefore, it is speculated that in the short term, the northeastern part of the study area will still be dominated by spatial transitions, while the southwestern part will still be Figure 10 shows that the overall direction of the gravity center of the comprehensive transition moved from the southwest to the northeast from 2001 to 2019. The migration direction of the gravity center of the spatial transition is basically the same as that of the comprehensive transition, while the functional center of gravity moves in the opposite direction from northeast to southwest. However, since 2013, the movement direction of the gravity center of the spatial transition and functional transition has converged, and the distance between the centers of gravity has been reduced, which is due to the narrowing of the economic level gap within the region. The development of society is a staged process. Therefore, it is speculated that in the short term, the northeastern part of the study area will still be dominated by spatial transitions, while the southwestern part will still be dominated by functional transitions.

dominated by functional transitions. From the migration speed of the transition center of gravity, the comprehensive, spatial, and functional transitions all show a slowdown (Table 3). Among them, the center of gravity of the comprehensive transition moved 31.0182 km, and the moving speed dropped from 2.9401 km/year to 1.2370 km/year. The center of gravity of the space transition moved 69.0618 km, and the moving speed decreased from 8.3573 km/year to 1.0814 km/year. The functional transition center of gravity moved 38.5782 km, and the moving speed decreased from 3.2398 km/year to 1.0254 km/year. This was mainly the result of being influenced by the driving forces of socioeconomic transition. First, the central government has focused on high-quality regional development rather than on high-speed development. Therefore, the economic growth rate has slowed, which has led to a slowdown From the migration speed of the transition center of gravity, the comprehensive, spatial, and functional transitions all show a slowdown (Table 3). Among them, the center of gravity of the comprehensive transition moved 31.0182 km, and the moving speed dropped from 2.9401 km/year to 1.2370 km/year. The center of gravity of the space transition moved 69.0618 km, and the moving speed decreased from 8.3573 km/year to 1.0814 km/year. The functional transition center of gravity moved 38.5782 km, and the moving speed decreased from 3.2398 km/year to 1.0254 km/year. This was mainly the result of being influenced by the driving forces of socioeconomic transition. First, the central government has focused on high-quality regional development rather than on high-speed development. Therefore, the economic growth rate has slowed, which has led to a slowdown in the migration speed of the center of the cultivated land transition.

in the migration speed of the center of the cultivated land transition.

**Figure 10.** Path of gravity center of the CLUT. **Figure 10.** Path of gravity center of the CLUT.

**Table 3.** Speed of gravity center of the CLUT (km/year). **Table 3.** Speed of gravity center of the CLUT (km/year).


#### **5. Discussion**

#### *5.1. Comparison of the Hidden Causes of the CLUT*

Combined with the research results, this paper analyzes the driving factors of the CLUT. At present, some scholars have carried out the related research from an empirical perspective. Here, we selected several representative studies that measured and calculated the influencing factors of the cultivated land spatial transition or functional transition (Table 4). Through the comparison results, it is found that socioeconomic factors such as the decline in the agricultural population and regional economic development; increasing social demand; physical geographical factors such as the location, topography, hydrogeology, and soil types of cultivated land; and national-led policy factors all promote the CLUT.

The results show that the changes in the spatial morphology of cultivated land are mainly reflected in the reduction in the amount of cultivated land caused by the construction of urban and rural housing sites. Cultivated land generally changes in scale and intensification. However, there is still a small amount of cultivated land that moves toward intensification, because the improvement of living standards of urban residents has created high-end demand for "slow growing" crops. The country's greening policy also affects the area distribution of cultivated land crops. It can be seen that policies and social needs strongly influence the cultivated land-use direction. Furthermore, with the improvement of the regional socioeconomic level and the implementation of national culture and tourism policies, the functions of cultivated land have developed in a diversified way, such as in cultivated land-cultural functions and landscape functions. There are few studies on the empirical verification of the impact of engineering and technological factors on cultivated land. Nevertheless, engineering technology assists in the leveling and restoration of cultivated land.


#### **Table 4.** Comparison of hidden causes of CLUT.

#### *5.2. Policy Implications*

It can be seen from the above evaluation results that the degree of the CLUT between regions is imbalanced. If the CLUT meets the socioeconomic stage, then it can promote social development, but if it does not meet the socioeconomic stage, then it may hinder socioeconomic development. Therefore, policymakers need to clarify the leading factors of the CLUT, take social development and people's needs as guidance, and fully consider the regional differences in the CLUT to formulate cultivated land utilization policies. Based on the above analysis, we found that the relatively developed northeast region of the study area has a strong spatial transition of cultivated land, while the relatively underdeveloped economy of the southwest region has a strong functional transition. For areas with a strong spatial transition, urban construction has a greater demand for land, and people's demands are more abundant. The main goal should be to clarify the relationship between cultivated land use and social demand, and then promote the implementation of measures to compensate for the external cost of the loss of the cultivated land quantity in the following ways. First, it is necessary to control the amount of urban land supply, increase the level of land intensity, and strengthen the protection of basic farmland. Second, this study has demonstrated that the planting structure and type of cultivated land must not only match the needs of society but also meet sustainability requirements. Finally, a cultivated land landscape improvement plan should be established to ensure the degree of concentration and contiguous farmland.

For areas with strong arable land function transitions, the main goal should be to achieve the balanced development of various functions of cultivated land as follows. First, the reform of agricultural modernization should be deepened, land should be consolidated, the soil fertility should be improved, and farmland production efficiency should be increased. In addition, it is necessary to increase agricultural subsidies and absorb agricultural labor. Most importantly, it is essential to develop green agriculture from the perspective of ecological security and innovate agricultural ecological compensation mechanisms. Through these strategies, we can stimulate the endogenous development

momentum of agriculture and realize the saving, green, and efficient use of cultivated land. In addition, both the overall and local CLUTs in the study area have positive aggregation effects, which indicates that the CLUT is a systematic problem, and there is a connection between the CLUTs in neighboring areas. Thus, it is necessary to strengthen regional cooperation, facilitate agricultural marketization and information construction, and invigorate agricultural operation mechanisms.

#### *5.3. Limitations and Prospects*

The CLUT is an inevitable consequence of socioeconomic transition. In previous studies, scholars have given more attention to changes in the amount or functional structure of cultivated land, while the comprehensive transition process of the cultivated land spatial and functional morphology has not received enough attention. Therefore, this study serves as a useful exploration to evaluate the CLUT and provides a reference for future research. The advantages of this research are as follows. First, this study combined quantitative and qualitative considerations to construct a "spatial–functional" integrated framework to identify the law of the CLUT. The transition of the cultivated land-use morphology is the dominant and recessive manifestation of CLUTs. This parameter is a comprehensive identification of the CLUT. Thus, compared with other regions, the main grain-producing areas have more important tasks for cultivated land protection and food security.

This research provides a novel perspective and content, but it still has some shortcomings. The evaluation of the CLUT is a complicated task, and a unified and standardized evaluation system needs to be established. In this study, natural factors are not considered in the "spatial–functional" comprehensive framework and should be included in subsequent studies. In addition, the defects of China's current farmland management regulations and property rights system have led to a decline in the quality of arable land. Moreover, the internal changes in cultivated land are more difficult to detect than the external changes. Therefore, research on the scientific and effective comprehensive evaluation systems for the transformation of cultivated land function forms should be the focus of future CLUT research. Subsequent research objects could be further enriched, such as the city scale, village scale, or field scale, especially in semi-urbanized areas where land conflict is more prominent and cultivated land protection is under great pressure. In addition, it is also a key consideration to put forward regulatory policies for the CLUTs in typical regions according to local conditions. In the future plan of this study, the spatial econometric model can be used to quantitatively analyze the core driving factors of CLUT.

#### **6. Conclusions**

This paper analyzes the mechanism of CLUT and evaluates the CLUT characteristics in the main grain-producing areas in the middle and lower reaches of the Yangtze River from 2001 to 2019 based on the "spatial–functional" integrated framework. The CLUT index of 71 prefecture-level cities was calculated, and then the magnitude, spatial correlation, direction, and speed of the inter-regional CLUT were analyzed.

The results show that the comprehensive transition index of cultivated land use continued to increase from 0.0480 to 0.0711 during the period. It can be said that social and economic factors have driven the acceleration of CLUT. In particular, the speed of functional transition is stronger than that of spatial transition, because the functional changes of cultivated land are directly intervened by human needs. However, the difference in the transition index between regions significantly expanded, and the transition range increased from 0.0345 to 0.0641. Such evidence suggests that the CLUT in the flat terrain area is larger than that in the mountainous area. Due to the advantages of terrain, the economic development, urbanization, and population growth of the plain area are strong, and the CLUT is fast.

The CLUT in the study area exhibited a positive aggregation effect and strengthened in the period. The degree of aggregation of the spatial and functional transitions increased from 0.3776 to 0.4673 and from 0.2127 to 0.2952, respectively. The CLUT of high-high agglomeration areas was concentrated in the northeast and southwest of the study area, and the low-low agglomerations areas were essentially distributed in the central region. This means that there is a spatial relationship between the CLUT in a region and its surrounding areas, and the activities of cultivated land used by humans are not separated.

The center of gravity of the CLUT has shifted from the southwest to the more economically developed northeast region. and the center of gravity migration speed of comprehensive, functional, and spatial transitions decreased from 2.9401 km/year to 1.2370 km/year, 8.3573 km/year to 1.0814 km/year, and 3.2398 km/year to 1.0254 km/year, respectively. Indeed, socioeconomic factors are often the main driving force behind the CLUT. In the current stage of China's economic slowdown, optimizing the morphology of cultivated land may be particularly important when adjusting the existing cultivated land management policy.

**Author Contributions:** Conceptualization, T.L. and S.F.; methodology, T.L., X.Z., G.W. and J.T.; software, S.F. and H.H; validation, T.L. and S.F.; formal analysis, T.L.; investigation, S.F.; resources, X.Z.; data curation, H.H.; writing—original draft preparation, T.L. and S.F.; writing—review and editing, T.L., G.W. and J.T.; visualization, S.F.; supervision, X.Z.; project administration, T.L. and X.Z.; funding acquisition, H.H. All authors have read and agreed to the published version of the manuscript.

**Funding:** This study was supported by the National Natural Science Foundation of China (No. 71864016 & 42261049), the Postdoctoral Science Foundation of China (No. 2017M622098), the Major Project of Social Science Foundation of China (21&ZD185), the Jiangxi Postdoctoral Science Foundation (No. 2017KY55), the Postdoctoral Daily Funding of Jiangxi Province (No. 2017RC036), the Science and Technology Project of Jiangxi Education Department (No. GJJ200509 & GJJ200542), the Humanities and Social Sciences Project of Jiangxi Education Department (No. JC20201), and the Student Research Project of Jiangxi University of Finance and Economics (No. 20210913221051660).

**Institutional Review Board Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Acknowledgments:** We thank the editors and anonymous reviewers for their very constructive remarks in preparing the final version of the paper. We also thank all authors for their contributions and joint work to complete the paper. We are solely responsible for the opinions expressed in this article.

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

#### **References**

