1. Introduction
Cultivated land is the basic resource of human survival and development [
1,
2]. Farmland protection is of great importance for food security and social stability, especially given the dual impact of COVID-19 and regional tensions [
3,
4]. Over recent decades, developing countries are characterized by a decrease in rural land use and an increase in urban land use through urbanization [
5,
6]. In China, where urbanization has reached 60%, the cultivated land area only accounts for one-eighth of the total land area. With the acceleration of urbanization, cultivated land area is still shrinking unceasingly, which is an indisputable fact [
7,
8]. In this case, it is particularly important to make full and reasonable use of every inch of cultivated land and improve the cultivated land use efficiency (CLUE) [
9,
10]. What is more, the redistribution of urban and rural labor forces and cultivated land brought by urbanization will inevitably affect the CLUE [
11,
12]. Therefore, understanding the relationship between urbanization and CLUE is crucial to the sustainable development of cultivated land [
13,
14,
15].
The Yangtze River Economic Belt (YREB) covers 25% of China’s land area and accounts for more than 40% of the population and Gross Domestic Product (GDP) [
16]. It is the economic belt with the most vitality and development potential in China, with self-evident importance to the economy. However, with dramatic urbanization and industrialization, YREB is also facing the problem of increasingly scarce cultivated land resources. The 14th Five-Year Plan proposes to improve the efficiency of resource utilization and promote the coordinated and sustainable development of the middle and lower reaches of the YREB and the eastern, central and western regions. Under the new development concept, promoting high-quality development of the YREB, especially striking a balance between ecological and environmental protection and economic growth, is a major strategy for China’s overall development. Cultivated land is the most important factor of production in agricultural development. Therefore, improving the CLUE has become an urgent issue in the face of dwindling arable land in YREB [
17]. The rapid urbanization of the YREB inevitably has brought about the decline of the cultivated land area. Does it do the same to the CLUE? What is more, how do we handle the relationship between urbanization and cultivated land use in the YREB? How can YREB better realize the coordinated development of economy and ecology in the process of urbanization? Figuring out these problems has become important content in studies on YREB.
To date, research on cultivated land mostly focuses on the evaluation of CLUE or the quality of cultivated land. Scholars have reached different conclusions on the trend of CLUE based on different methods or sampling. Some suggested that CLUE was on the rise. Kuang et al. [
18] analyzed the CLUE of China and showed that there was an increasing trend in CLUE from 2000 to 2017. Besides, most provinces had much lower levels of CLUE with significant spatial disparities [
19]. Herzig et al. [
20] presented a novel approach to assess explicitly the resource-use efficiency of land use and the test assessment showed that the resource-use efficiency could be increased by 11% for both nitrate and sediment loss in the Haean catchment, South Korea. Masini et al. [
21] presented a multidimensional analysis of land-use efficiency in terms of the per-capita built-up area over 417 metropolitan regions from 27 European countries and the results indicated that wealthier cities were characterized by higher land-use efficiency.
Others concluded that CLUE was declining. Fei et al. [
22] and Guo et al. [
23] thought the CLUE in China had decreased overall from 2004 to 2017, showing a decreasing trend from the east to the central and west. It has not evolved towards harmonious development of the environment and economy. Xie et al. [
24] found that the net loss of topsoil through cultivated land use is 1.75 times the resilience of the cultivated land system, which places tremendous pressure on cultivated land protection. Lu et al. [
25] took 65 cities of the Yellow River Basin as the basic evaluation unit and found that the CLUE presents a trend of “rising first and then falling”. Yang et al. [
26] indicated that socioeconomic development level, agricultural science and technology investments, carbon emission reduction, and agricultural pollution control could all effectively improve the CLUE in the YREB.
As for the impact of urbanization on cultivated land, most scholars hold that urbanization was one of the main reasons for the decrease in cultivated land resources in China [
27]. The evolution of cultivated land is driven by climatic, economic, and social factors, of which population density is one of the most important factors [
8]. With the development of urbanization, a large amount of cultivated land had been transformed into industrial land, infrastructural land and residential land, resulting in the reduction of cultivated land [
28,
29]. Yang et al. [
30] have explored the trajectory and driving paths of rural transformation in traditional agricultural areas, taking the Loess Plateau of China as an example. They found that regional urbanization was one of the key forces affecting traditional agricultural areas. Under the impact of urbanization and other factors, land use showed an eco-transformation from farmland to forest land, and from cultivated land gradually to uncultivated land. Tian et al. [
31] found that the expansion of non-agricultural land had been mainly characterized by the growth of industrial land by combining Landsat TM images and land use maps based on a site survey. This is in line with Haroon and Mohd [
5], which concluded that the amount of built-up area had increased dramatically whereas the area under agriculture had decreased drastically due to urban expansion from 1991 to 2010. Li et al. [
32] measured changes in rainfed land, paddy land, irrigated land and orchards in the peri-urban area throughout a period of rapid urbanization and indicated that irrigated land and orchards were mainly distributed within urban-adjacent areas, and paradoxically showed an evident decrease in quantity across time. Hou et al. [
33] systematically analyzed how urbanization influenced the CLUE and concluded agglomeration and barrier effects had a significant negative effect on the CLUE, while driving and feedback effects presented significant positive effects. However, other scholars argued that urbanization was conducive to the improvement of land use intensity and can protect cultivated land. Since the per capita construction land in urban areas was less than that in rural areas, population urbanization would not only not increase the occupation of cultivated land, but also could protect cultivated land [
34]. Li et al. [
35] found strong connections between the land conversion rates and urban–rural transformation intensity in the Bohai Rim region. That is, rapid land conversion normally takes place in counties/districts of low initial level of urban–rural transformation.
Although existing studies have provided rich insights into understanding the relationship between urbanization and CLUE, more efforts are still needed to account for the relationship between the two. First, studies mostly have focused on the impact of urbanization on urban land efficiency [
36,
37,
38] or the reduction of the cultivated land area [
39]. The impact of urbanization on CLUE has been rarely studied, especially along the YREB, the most important driving force for China’s economic development. Second, there is abundant research on the measurement of CLUE in the existing literatures. However, when it comes to the impact of urbanization on CLUE in YREB, the measurement of CLUE lacks consideration of environmental issues. Besides, urbanization is accompanied by the gathering of the population into cities and the expansion of urban space. These are not fully recognized in previous studies, leading to errors or deviations in estimating and analyzing process. Third, the measurement of CLUE mainly adopts the data at the provincial level, while the data at the municipal level are rarely used.
The contribution of this study is as follows: (1) Compared with previous studies, this paper focuses on the differentiated impact of population and land urbanization on CLUE in the YREB. The result makes a clear understanding of the impact of urbanization on CLUE, which is of great significance for promoting the high-quality development of the YREB. (2) Considering the impact of environmental pollution, this paper adopts the SBM-Undesirable method to evaluate the CLUE in YREB. On this basis, we use the spatial effect model to analyze the impact of urbanization on CLUE and its regional differences, providing a reference for decision makers to rationally plan urban layout and balanced development of cultivated land resources in the YREB (3). Different from previous studies on CLUE in YREB, which use data at the provincial level, this paper uses the data of 108 cities in YREB to measure CLUE and analyze its evolution trend. This has important reference value for reducing cultivated land-use carbon emissions and promoting green and low-carbon transformations of cultivated land for YREB.
The remainder of this paper is as follows. In
Section 2, we introduce the study area and the method of spatial empirical analysis.
Section 3 carries on the spatial empirical analysis.
Section 4 is the discussion.
Section 5 is the conclusion with some policy implications.
4. Discussion
With the advancement of urbanization in the YREB, the contradiction between urbanization and cultivated land has become increasingly prominent. In the case of limited cultivated land, how to improve the CLUE is an inherent requirement to promote the high-quality development of the YREB. The six provinces in YREB are China’s main grain-producing areas, which play an important role in ensuring national food security. At the same time, the YREB is also the region with the fastest urbanization development in China. Therefore, how to handle the relationship between the two becomes increasingly crucial.
Urbanization is mainly manifested in two dimensions, including population and land. With the large-scale transfer of the rural population, the population in rural areas is hollowing out seriously, contributing to the inevitable change of the traditional farming mode. The expansion of urban space leads to a large number of encroachments on cultivated land. The decentralized management of land makes it difficult to realize the scale effect. Moreover, the damage to soil caused by environmental pollution in the process of land urbanization is difficult to repair in a short term. There is much in the literature on the impact of urbanization on urban land use efficiency, while few studies focus on CLUE, especially empirical studies on city-level norms. Based on data of 108 cities in YREB, the spatial effect model test shows that population urbanization and land urbanization have positive and negative effects on CLUE, respectively, which is consistent with the conclusion of Gao and Wang (2020) [
50].
Existing studies on the relationship between urbanization and CLUE in the YREB mainly focus on the whole sample [
17,
26], and there are few studies on the impact of urbanization on CLUE of different regions. Through the heterogeneity test, this paper specifically analyzes the impact of urbanization in various regions on the utilization efficiency of cultivated land. It is found that population urbanization and land urbanization in the upper, middle and lower reaches have significantly different effects on the efficiency of cultivated land due to the influence of economic development level geographical factors and Ecological orientation. The results of the study are conducive to strengthening inter-provincial coordination in ecological and environmental protection in the YREB and realizing the synergy of the upper, middle and lower reaches in promoting high-quality development.
In terms of indicator selection, there are many measurement methods for urbanization. Future research may take economic urbanization, social urbanization and the comprehensive level of urbanization into consideration. Due to the limitation of data availability, the carbon emissions estimated by the amount of chemical fertilizer used are taken as the unexpected output when SBM is used to calculate the CLUE. This may influence the conclusion to some extent. In addition, this paper has adopted the urban level as the scale of spatial analysis. Smaller scales, such as the county-level units, could be considered in future research.
5. Conclusions
With the advancement of urbanization in the YREB, the contradiction between urbanization and cultivated land has become increasingly prominent. In the case of limited cultivated land, how to improve the CLUE is an inherent requirement to promote the high-quality development of the YREB. The six provinces in YREB are China’s main grain-producing areas, which play an important role in ensuring national food security. At the same time, the YREB is also the region with the fastest urbanization development in China. Therefore, how to handle the relationship between the two becomes increasingly crucial. Existing studies pay more attention to the impact of urbanization on urban land use efficiency, while there are few studies on CLUE, especially empirical studies on city-level norms. Based on the panel data of 108 cities in the YREB from 2001 to 2019, this paper adopts the SEM to investigate the impact of urbanization on CLUE. The main conclusions are as follows:
1. The CLUE of the YREB presents a spatial distribution trend of high or low agglomeration during the sample period. The high-value cluster has changed from a multi-core cluster to a two-core cluster. In 2001, the high-value areas were mainly concentrated in southern Yunnan, northern Anhui, Sichuan and Chongqing. In 2019, the high-value areas were mainly around the Chengdu-Chongqing urban agglomeration and the northern urban agglomeration of the Yangtze River Delta. The low values are mainly concentrated in provinces such as Jiangxi.
2. The spatial effect model test shows that population urbanization has positive effects on CLUE, while land urbanization has negative effects on CLUE. The positive effect of population urbanization is mainly due to the scale effect brought by the population agglomeration caused by the rapid urbanization of the YREB. With the large-scale transfer of the rural population in YREB, the population in rural areas is hollowing out, seriously contributing to the inevitable change of the traditional farming mode. Meanwhile, urbanization provides capital, technology and professional talents for agricultural development, and promotes the expansion and upgrading of agricultural product consumption markets. This is conducive to rural scale management, improving the efficiency of cultivated land use. The negative effect of land urbanization may be due to the decline of cultivated land quality caused by the indiscriminate occupation of cultivated land and the destruction of resources and the environment in the process of land urbanization. The expansion of urban space leads to a large number of encroachments on cultivated land. The decentralized management of land makes it difficult to realize the scale effect. Moreover, the damage to soil caused by environmental pollution in the process of land urbanization is difficult to repair in a short term.
3. Urbanization in different regions of the YREB has different effects on CLUE. For population urbanization, the lower reaches have a positive impact on the CLUE, while the middle and upper reaches have no obvious effect on CLUE. Compared with the middle and upper reaches, the high level of urbanization in the lower reaches of the region has brought scale effects to the efficiency of cultivated land. For land urbanization, the downstream has significantly promoted CLUE. The reason for this may be related to the conversion of a large number of dry land to paddy land. The coefficient of land urbanization in the middle is significantly negative. The region is dominated by medium-sized cities, of which the degree of urbanization coordination needs to be improved. The upper reaches are dominated by woodland and grassland, and the land urbanization rate is relatively slower. Therefore, the upper has no significant impact on the CLUE.
Based on the conclusion, we propose the following policy implications:
1. Improve the quality of the three major urban clusters along the YREB, releasing the huge potential from population urbanization. The YREB is the most rapidly urbanized region in China, but the economic development levels of the nine provinces and two cities are very different. The government should deepen inter-city cooperation in the Yangtze River Delta city cluster, the midstream city cluster and the Chengdu-Chongqing city cluster in terms of ecology, industry and transportation network construction. Define the functional positioning of core cities, taking core cities such as Shanghai, Nanjing, Wuhan, Chongqing and Chengdu as the most important economic growth poles within the belt. Thus, they can play a radiating role in the surrounding urban agglomeration. Yibin City of the Sichuan Province should assume the role of coordinator and promoter of upstream urban agglomeration, strengthening the county’s economy. Counties in the upper reaches of the YREB are developing at a relatively high level, while those in the lower reaches are lagging behind. The government should increase transfer payments and counterpart assistance to these regions, promote the upgrading of urban consumption structure and advocate for the concept of urban green life. This is conducive to promoting green agricultural production and reducing the input intensity and carbon emission intensity of agricultural chemicals.
2. Build an ecologic protective screen in the upper reaches of YREB. Prohibit the exploitation of high-quality cultivated land resources and strictly implement the compensation system for cultivated land. In particular, the middle and upper reaches, as a zone of ecological fragility and ecological barrier construction, must always adhere to the supremacy of ecology. Avoid supplementing high-quality cultivated land with low-quality cultivated land, and pay attention to restoring and improving the quality of cultivated land in the process of implementing the balance between the occupation and compensation of cultivated land. Optimize the tillage layout of paddy and dry land and farm intensively according to geographical conditions and water environment capacity, improving CLUE.
3. Complement the shortcomings of the agricultural labor force with the new agricultural management system. The rapid urbanization of the population in the YREB has prompted a shift from traditional to modern agricultural methods. Cultivating new agricultural management subjects and exploring the diversification of agricultural socialized services can offset the negative effect of rural labor shortage and improve the scale efficiency of land.
4. Detailed regulations related to the cultivated land protection in YREB must be deployed. To date, the standards for soil pollution, pesticide use and agricultural sewage directly related to the YREB are not clear. The 11 provinces and municipalities may continuously complete the formulation of relevant standards under the coordination of the Leading Group for the Development of the Yangtze River Economic Belt and the Coordination Committee for the Green Development of the Yangtze River Economic Belt.