**1. Introduction**

Cultivated land is a key component to achieve sustainable development and ensure food security [1]. China has the third largest cultivated area in the world, but the per capita level is less than 1/2 of the global average. Since 1978, when socioeconomic reforms were implemented, China has experienced rapid development [2,3]. In 2000, in the opening year of the Tenth Five-Year Plan, the Chinese government stated that China's conditions for promoting urbanization were gradually maturing, and it was necessary to accelerate the implementation of an urbanization strategy [4,5]. Therefore, Chinese urbanization has entered an accelerated development stage. The urbanization levels increased from 36.20% to 60.60%, and the average annual urbanization growth rate remained at 1.28% from 2000 to 2019 [6]. However, this achievement also led to corresponding social, economic, and ecological problems. These problems include disorderly construction land expansion, inefficient land use [7], abandoned villages [8,9], and the overexploitation of ecological resources, which lead to a significant depletion of cultivated land resources and serious nonagriculturalization and pollution [10]. With this context of the times, China's cultivated land

**Citation:** Lv, T.; Fu, S.; Zhang, X.; Wu, G.; Hu, H.; Tian, J. Assessing Cultivated Land–Use Transition in the Major Grain-Producing Areas of China Based on an Integrated Framework. *Land* **2022**, *11*, 1622. https://doi.org/10.3390/land11101622

Academic Editor: Francisco Manzano Agugliaro

Received: 19 August 2022 Accepted: 20 September 2022 Published: 22 September 2022

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**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

conditions are undergoing drastic changes. Accordingly, the cultivated land-use transition (CLUT) has become one of the most urgent issues to be addressed by the academic and governmental sectors. Land-use transition (LUT) originated in the 1990s at the University of Aberdeen in Scotland as the geographer Mather's exploration of the forest transition hypothesis, which involves corresponding changes in land-use morphology during social development [11,12]. The research on LUT has expanded from forests to grasslands, waters, and cultivated land. Meanwhile, from the research perspective of land change from landuse/cover change (LUCC) to land-change science (LCS), LUT has become a frontier hotspot of land-system science [13].

In fact, CLUT is the main component of LUT, which continues the research results of LUT in terms of concept and connotation, and is a trend turning point of cultivated land-use morphology under long-term changes. In other words, it is a process of transition from one stable state to another stable state [14]. Existing studies usually decompose cultivated land-use morphology into dominant and recessive [15]. The former includes the amount of cultivated land, planting structure, and landscape pattern attributes. The latter includes attributes that are not easy to be directly observed, such as cultivated land quality, property rights, and management methods, and can only be obtained through investigation, testing, and analysis [16]. This applies, for example, to the soil chemical content of cultivated land. The dominant morphology of cultivated land is the direct expression of its space utilization status; therefore, the dominant morphology is also called the spatial morphology, and the two are essentially the same [17]. In order to present the recessive morphology of cultivated land more intuitively, this study starts from the functional morphology of cultivated land for transition diagnosis. The functional morphology perspective of cultivated land corresponds to the human demand for cultivated land and is a comprehensive manifestation of recessive morphology [18].

Based on the definition of cultivated land pattern, the current research in this field generally covers the CLUT path, index construction, spatiotemporal differentiation characteristics, and driving mechanism [19] and its relationship to social and economic activities [20]. Regarding the path of CLUT, most studies mainly focus on the expression of a single path of cultivated land morphology. From the perspective of spatial pattern, it focuses on the study of land-use/cover change [21]. Research on the recessive pattern has a wide range of perspectives, such as changes in cultivated land productivity, monitoring of soil quality, and conversion of property rights [22–25]. There is still a gap in the research on combining spatial morphology and functional morphology to comprehensively evaluate CLUT. In terms of index construction, the evaluation of CLUT is mainly to quantify the morphological changes of cultivated land [26]. For different scholars, the understanding of CLUT performance is different, and the selection of indicators is also prone to differences, which reduces the comparability between different studies. For instance, when choosing the evaluation index of the social function of arable land, some researchers consider it to be the ability of cultivated land to solve farmers' work problems, and they select indicators such as agricultural income and the labor-carrying capacity of cultivated land; to the contrary, some researchers think that it is the faculty of cultivated land to produce food to feed the population, so the per capita food availability is selected for evaluation [27]. At the analysis level of the driving mechanism, the spatial econometric model is mainly used for quantitative research, and variables are selected from social and natural factors. However, qualitative research is the foundation of quantitative research, and the current logical analysis of the driving mechanism from a qualitative perspective is still relatively weak. In terms of the relationship with society and the economy, there are studies on the coupling and interaction mechanism of food production, agricultural–economic development, and rural labor transfer [28]. At the same time, CLUT is also usefully explored from the perspective of its ecological environment effect. At the regional level, the research mainly focuses on the national, provincial, and municipal regions. The cultivated land is mainly used for food production, and CLUT has a more profound impact on the main grain-producing areas than other areas. However, scholars have neglected the issue of

CLUT in the main grain-producing areas, which limits the guidance and reference value for formulating policies for sustainable use of regional cultivated land. To sum up, it can be seen that the relevant research on CLUT still has an incomplete evaluation framework, inconsistent index selection criteria, weak qualitative analysis of the driving mechanism, and gaps in regional research [29].

The main grain-producing areas have faced the various tasks of stable grain production, economic growth, industrial upgrading, and ecological protection [30]. The population and economy here are highly dense, which puts enormous pressure on the local land supply and ecological environment. Undoubtedly, urban development has changed the morphology of cultivated land. Therefore, this paper takes the middle and lower reaches of the Yangtze River as the research area. In addition, we attempt to construct a "spatial–functional" integrated framework to evaluate the CLUT. In particular, the study aims to: (1) identify and construct the connotation of CLUT from multiple dimensions; (2) build a comprehensive evaluation index system to achieve a scientific and effective quantitative evaluation of a regional CLUT; (3) reveal the spatiotemporal variation laws and characteristics of the CLUT in the main grain-producing areas; and (4) put forward targeted strategies for the optimal utilization and reasonable transition of cultivated land.

The marginal contributions of this study are mainly in the following four parts. (1) Based on the perspective of the comprehensive "spatial–functional" pattern to explore the spatiotemporal characteristics of CLUT, which expands the definition of cultivated land-use pattern and enriches the related literature of CLUT; (2) the selection of CLUT indicators under the two morphologies is subdivided and explained, which provides an evaluation system that can be used for reference; (3) the driving mechanism of CLUT is described from the theoretical level. The driving principles of natural and socioeconomic policy, technology, and other factors are analyzed. It lays a theoretical foundation for carrying out qualitative research; (4) considering the particularity of the main grain-producing areas, it provides a research basis for the formulation of cultivated land-use policies in the study area and similar areas.

#### **2. CLUT Interpretation Framework**

As the social stage develops from point A to point B (Figure 1), which is mainly affected by the natural environment, socioeconomic policy, and technology [31], to meet the needs of the social development stage, the cultivated land users will adjust their cultivated land utilization behavior through the actual conditions of the cultivated land, and the cultivated land-use morphology will change accordingly. When the social stage develops toward a higher point C, the original cultivated land-use morphology at point B should continue to be adjusted accordingly [32]. Therefore, for different scales, the CLUT is an iterative process of dynamic balancing of the human–earth system interactions and joint constraints [33,34].

Thus, this study divides cultivated land-use morphology into two aspects: namely, spatial and functional. Spatial morphology consists of the amount of cultivated land, landscape, and crop planting structure [35]. Functional morphology reflects the types of cultivated land functions, which is an inherent attribute [36]. According to the classification of land-use functions (LUFs), the functions of cultivated land are divided into the three basic functions of crop production, life support, and ecological maintenance [37]. Therefore, this study constructs a "spatial–functional" integration framework to identify and construct the mechanism of CLUT from multiple dimensions, which is helpful to comprehensively identify and evaluate CLUT.

**Figure 1.** Interpretation framework of CLUT. **Figure 1.** Interpretation framework of CLUT.

**3. Methodology and Data**  *3.1. Study Area*  The main grain-producing area is situated in Southern China at 24°29′–35°20′ N and 108°21′–121°57′ E. The study included 71 prefecture-level cities under the jurisdiction of the five provinces of Jiangxi, Hunan, Hubei, Anhui, and Jiangsu (Figure 2). The total area measures 81.19 × 104 km2, which is approximately 8.46% of China's total land area. The terrain here is flat, and it has abundant cultivated land resources. Meanwhile, the mild climate and abundant rainfall have laid a good foundation for China's agricultural production. In 2019, the urban area was 37,672.74 km2, and the cultivated land of this region was 21.77 × 104 km2, which account for approximately 4.64% and 26.82% of the total area, respectively. The grain output reached 15,617.47 × 104 tons, which is nearly one-quarter of the country's total grain output (National Bureau of Statistics of China (NBSC), 2020). With the improvement in the degree of economics and urbanization, and the change in social demand, the structure and methods of cultivated land use have undergone tremendous changes. (1) Cultivated land-use spatial transition: When the social development level is low, due to the unclear property rights of cultivated land and underdeveloped agricultural technology, the social awareness of cultivated land protection is relatively weak and there is a disorderly expansion in cities. To ensure people's rations, food crops have always been the main crops grown on cultivated land. With the progress of society and the gradual improvement of the agricultural system, people's skills in using cultivated land will continue to increase, and more attention will be given to promoting the sustainability of cultivated land use. The national government will take relevant measures to curb the reduction of the cultivated land area and ensure quality degradation so that the amount of cultivated land may show a trend of "decrease–stable–increase" [38]. For example, China currently implements strict cultivated farmland requisition–compensation-balance policies to ensure the stability of the amount of cultivated land. To facilitate agricultural production, people constantly adjust the distribution pattern of cultivated land plots through engineering means, and the landscape pattern of cultivated land will develop in a concentrated, continuous, and regular direction [39]. Moreover, against the background of enriched consumer demand, and driven by the economic interests of cultivated land operators, the arable land planting structure will show the characteristics of diversified development. However, if the proportion of grain planting is too low, then the government will introduce and implement relevant systems to control the trend of non-grain cultivated land. In general, the quantity, planting, and landscape patterns of cultivated land change in the course of social development.

(2) Cultivated land-use functional transition: For most farmers, agricultural labor can provide employment and income, and the harvested crops can satisfy rations, which maintains the farmers' livelihood, prevents the occurrence of social risks such as hunger and unemployment, and ensures the stable development of society [40]. At this time, an increased use of chemicals is often relied on to increase food production. In this way, it is easy to cause the decline of cultivated land quality and biodiversity, which restricts the ecological function of cultivated land.

The average patch area of cultivated land will increase, the variety of crops will be diversified, and the quality will be increasingly higher so that the production function will be enhanced. In the urbanization process, in the pursuit of higher income, the rural surplus labor force will be transferred to nonagricultural industries, which results in the reduction of farmland employment opportunities for farmers and ultimately affects the life-support function of cultivated land [41]. Moreover, as the extensive use of agriculture leads to ecological destruction, human beings have begun to understand and adjust their relationship with nature [42], reduce the use of pesticides and fertilizers, and promote green fertilizers. Thus, the ecological maintenance function of cultivated land has received much attention and has improved greatly.

Comprehensively, CLUT is a continuous and cyclic process [43] that not only depends on the influence of the social economy, policy, technology, and other factors, as well as the promotion of cultivated land-user behavior, but also demonstrates the influencing factors and the behavior of cultivated land users. The cultivated land user decides whether to adjust the decision-making and behavior mode of cultivated land use according to their satisfaction with the result of a CLUT. At the same time, the feedback of the CLUT can promote the change and generation of the driving factors. For example, to satisfy the endless demands of mankind, the cultivated land users try to continuously add chemical fertilizers in exchange for the output of cultivated land. However, the result may be the destruction of the cultivated land ecosystem [44]. To ensure sustainable development, policymakers need to issue corresponding policies to restrict the input of chemical fertilizers. Therefore, in the overall operation of the CLUT mechanism, the driving factors and transition results promote and restrict one another through the subject of cultivated land use to form a "multifactor drive → subject behavior change → CLUT → transition result feedback → new wheel drive" cyclical interaction process, which is also the internal model of the spatiotemporal dynamic evolution of cultivated land-use morphology.

#### **3. Methodology and Data**

#### *3.1. Study Area*

The main grain-producing area is situated in Southern China at 24◦290–35◦200 N and 108◦210–121◦570 E. The study included 71 prefecture-level cities under the jurisdiction of the five provinces of Jiangxi, Hunan, Hubei, Anhui, and Jiangsu (Figure 2). The total area measures 81.19 <sup>×</sup> <sup>10</sup><sup>4</sup> km<sup>2</sup> , which is approximately 8.46% of China's total land area. The terrain here is flat, and it has abundant cultivated land resources. Meanwhile, the mild climate and abundant rainfall have laid a good foundation for China's agricultural production. In 2019, the urban area was 37,672.74 km<sup>2</sup> , and the cultivated land of this region was 21.77 <sup>×</sup> <sup>10</sup><sup>4</sup> km<sup>2</sup> , which account for approximately 4.64% and 26.82% of the total area, respectively. The grain output reached 15,617.47 <sup>×</sup> <sup>10</sup><sup>4</sup> tons, which is nearly one-quarter of the country's total grain output (National Bureau of Statistics of China (NBSC), 2020). With the improvement in the degree of economics and urbanization, and the change in social demand, the structure and methods of cultivated land use have undergone tremendous changes.

#### *3.2. Explanation of the CLUT Assessment Indicators*

Based on the "spatial–functional" integration of the CLUT, the evaluation indicator system of the CLUT was established from the perspective of morphology. The indicators were selected based on a scientific analysis of cultivated land morphology and collaboration with scholars. The evaluation system consists of six factor layers and 18 indicator layers in spatial and functional morphology. The following is a brief summary of the reasons for choosing these indicators (Table 1).

**Figure 2.** The study area includes Anhui, Hubei, Hunan, Jiangsu, and Jiangxi Provinces. **Figure 2.** The study area includes Anhui, Hubei, Hunan, Jiangsu, and Jiangxi Provinces.

*3.2. Explanation of the CLUT Assessment Indicators*  3.2.1. Selection of the Evaluation Index for the Spatial Transition

Based on the "spatial–functional" integration of the CLUT, the evaluation indicator system of the CLUT was established from the perspective of morphology. The indicators were selected based on a scientific analysis of cultivated land morphology and collaboration with scholars. The evaluation system consists of six factor layers and 18 indicator layers in spatial and functional morphology. The following is a brief summary of the reasons for choosing these indicators (Table 1). (1) The index of the pattern of cultivated land quantity considers its total resources, area-change rate, and utilization degree [45]. The total area of cultivated land can reflect the resource endowment conditions of a region, and the area-change rate can embody the change in the amount of cultivated land. The reclamation rate can embody the change in the cultivated land-use area. Therefore, the quantity pattern of cultivated land is measured by three indicators: namely, the total area of cultivated land (x1), the rate of area change (x2), and the reclamation rate (x3).

(2) Cultivated land planting pattern evaluation indicators consider the spatial change in the cultivated land per capita planting area, the planting intensity, and the planting structure. The per capita cultivated land area owned by planting industry employees can reflect the area of cultivated land that can be planted per capita. The proportion of the grain and cash crop planting area can reflect the planting structure of arable land. The multiple cropping index can measure the planting intensity of cultivated land. The expansion of the sown area of arable land will lead to the exponential growth of multiple cropping. Therefore, we choose the per capita cultivated land area (x4), the proportion of the planting area for food crops and cash crops (x5), and the multiple cropping index (x6) to characterize the changes in the cultivated land planting pattern.





i=1

the type of crops, and n is the number of types of crops. Based on the aforementioned, the area, select food crops, vegetable crops, melon crops, and oil crops for calculation.

(3) The evaluation index of the cultivated land landscape pattern should represent the transition of its landscape morphology in agricultural production activities [43]. The landscape pattern mainly includes the degree of fragmentation and agglomeration, and the irregularities of farmland patches. This represents the concentration of cultivated land plots and the convenience of cultivators to plant. If cultivated land is relatively fragmented and has an irregular shape, then this will hinder large-scale development and mechanization. Therefore, the transition of the cultivated land landscape pattern is characterized by the fragmentation degree (x7), aggregation degree (x8), and landscape patterns index of cultivated land patches (x9).

#### 3.2.2. Selection of the Evaluation Index for the Functional Transition

(1) The crop production function evaluation indicators are considered from the two aspects of the economic value output capacity and the crop output capacity of cultivated land. The gross value of cultivation is an important manifestation of the productive capacity of the cultivated land economy. The output of food crops and cash crops can reflect the production value of agricultural products on cultivated land [37]. Therefore, the crop production function of cultivated land is calculated by using the average economic output value (x10), average grain yield (x11), and average cash crop yield of cultivated land (x12).

(2) The life-support function evaluation index should show the ability of cultivated land to guarantee the rural population's employment, income, and social food security [42]. The proportion of planting in the rural population represents the employment absorption capacity of cultivated land for the rural population. The ratio of per capita agricultural income to total income represents the population's economic dependence on cultivated land. The per capita food guarantee rate represents the degree to which people depend on cultivated land for survival. Thus, the proportion of employees in the planting industry (x13), the per capita food guarantee rate (x14), and per capita agricultural income ratio (x15) are selected to represent the life-support function of arable land.

(3) The evaluation indicators of the ecological maintenance function take into account the negative pressure of chemical substances on cultivated land ecosystems, the resilience of the ecosystems, and the resistance to natural disasters [46]. When the chemical load of cultivated land is heavier, the degree of ecological damage to cultivated soil is greater. When the crop species diversity index is higher, the resilience of cultivated land ecosystems is stronger. When the effective irrigation area is larger, the drought resistance of cultivated land is stronger. The reasonable and effective use of cultivated land will decrease ecological damage and maintain the balance of the ecosystem. Therefore, the ecological maintenance function is characterized by the chemical load of cultivated land (x16), the diversity of crop species (x17), and the effective irrigation area ratio (x18).

### *3.3. Methodology*

#### 3.3.1. Entropy Weight Method

The entropy weight method is currently the most widely used objective weighting method, which can effectively eliminate the dimensional influence. This study uses the entropy weight method to determine the weight of each evaluation index, which reflects the contribution of each index to the CLUT. According to the evaluation index system of CLUT, the CLUT index is the sum of the products of each functional index and its respective weight. Since this method is relatively common, the specific formula refers to [47].
