1. Introduction
China has always been the major grain producer and consumer in the world. Ensuring the steady growth of agricultural output is important for the nutrition and health of Chinese citizens. In order to ensure the stable development of agricultural production, the Chinese Government issued the NO.1 Central Documents related to agriculture from 2004 and China’s grain production has increased for 12 consecutive years. The continuous growth of agricultural output in China can be attributed to two reasons: the increase in agricultural input factors such as labor force, cultivated land, machinery, pesticide and fertilizer; and the sustainable growth of agricultural total factor productivity (TFP) [
1,
2]. It is generally believed that the development of China’s agricultural production has been driven by high input. Therefore, the growth of agricultural TFP is seen as a better pathway for sustainable development.
The calculation and correction of TFP has always been a topic if interest in academic studies [
3,
4,
5,
6]. Robert Solow was the first to measure TFP [
7]. He proposed the slow residual method to reflect the contribution of technological progress after eliminating the contribution of various input factors. Furthermore, a new production function with controlling unobserved shocks was proposed to solve simultaneity problems [
8,
9]. In addition, DEA as a nonparametric approach is used to measure efficiency and productivity of decision-making units [
10,
11]. Meanwhile, SFA as a parametric approach with specific function setting is generally employed to measure technology efficiency based on panel data [
12,
13].
Agricultural TFP is affected by various factors [
14,
15,
16,
17]. Gutierrez found that geographical location, international and domestic R&D investment are important factors affecting agricultural TFP [
18]. From the perspective of convergence and divergence of agricultural TFP, Paudel et al. found that there was no convergence trend in agricultural TFP among states in the United States, and inter-state differences in agricultural TFP were affected by the quality of human capital [
19]. By measuring the substitution elasticity of agricultural input factors, Gong found that agricultural technological progress and continuous factor input alternately promoted the growth of agricultural output in China [
20].
Urbanization is also considered as one of the important factors influencing agricultural TFP, because urban–rural factor allocation market and agricultural production technology are profoundly affected [
21,
22]. Some scholars have discussed that the urbanization process has imposed a fundamental impact on China’s agricultural production [
23,
24,
25]. Zhao found that the short-term negative effect of urbanization on the technical efficiency of grain production is smaller than the long-term positive effect, and the effects vary among different functional areas of grain in China [
26]. Wu et al. pointed out that population urbanization and employment urbanization contribute to promoting the growth of agricultural TFP in China by estimating the panel fixed effect model. Latest research results of Liu et al. show that human capital, level of urbanization, and development flow to agriculture promotes agricultural TFP growth in south and southeast Asian countries [
27]. However, Cheng drew the opposite conclusion that population urbanization and employment urbanization have negative effects on the improvement of agricultural carbon productivity [
28,
29]. In addition, Cai et al. found that the coupling degree between China’s new urbanization and the agro-ecological environment is in the antagonistic stage, so there is still great room for improvement [
30].
China comprehensively promotes the process of urbanization. According to the China Statistical Yearbook (2020), China’s permanent urban population reached 848.43 million and the urbanization rate reached 60.60%. In order to ensure the sustainable growth of agricultural TFP, it is necessary to analyze the mechanism of urbanization on agricultural TFP. On the one hand, urbanization can change the allocation of resources between urban and rural areas. Cities can provide the countryside with machinery, seeds, and advanced technology to improve agricultural total factor productivity continuously. On the other hand, urbanization also brings a series of problems to agriculture, such as a lot of labor migration from rural areas to urban areas, the occupation of farmland by urban construction, and the ecological pollution caused by urbanization and industrialization [
31], which may negatively inhibit the sustainable development of agricultural TFP in China. Therefore, urbanization in China may have various effects on agricultural production, which has been explored a lot [
32].
2. Theoretical Analysis
Urbanization may have both positive and negative effects on agricultural production. From the perspective of labor migration, on the one hand, with the migration of rural labor force to non-agricultural industries, the marginal productivity of rural labor will be significantly improved, contributing to the increase in labor productivity, thus improving the income level of farmers to a certain extent [
33,
34]; on the other hand, due to the restriction of the Hukou-household registration system in China, the young and middle-aged rural labor force pursue better job opportunities in the cities [
35], which results in more and more women, children and the elderly left in the countryside, so the quality of human capital in rural areas gradually becomes worse [
36]. Additionally, the development of urbanization promotes the large-scale intensive use of rural land so as to improve land production efficiency [
37]; alternatively, urbanization will also lead to the occupation of large amounts of arable land, especially in eastern and central regions of China [
38].
The relationship of urbanization and agriculture has aroused the attention of many scholars. From the perspective of urban-rural income gap and agricultural growth, there may be a U-shaped relationship, which diverts rural resource out of agricultural sector to urban sector [
39,
40]. As for urbanization and agricultural productivity, increasing population density increases agricultural productivity at the rural-urban fringe, while increasing urban fragmentation may have a detrimental effect on agricultural productivity at low levels of fragmentation [
41].
It is also worth noting that urbanization and agricultural production have spatial attributes. The urbanization development of the surrounding areas is likely to have a certain impact on that of local regions. The exchange of population, land, investment and technology in adjacent regions will interact and influence each other [
42]. Similarly, agricultural TFP may have spatial convergence [
43]. This phenomenon is more easily observed when two adjacent regions have similar geographical characteristics. Natural conditions, agricultural production mode, economic characteristics, and agricultural technology diffusion of adjacent regions have a certain degree of correlation, which can be understood as geographical, economic, and institutional correlation [
44]. Therefore, the impact of urbanization on agricultural TFP may have a strong spatial spillover effect.
In the view of the complex relationship between urbanization and agricultural TFP, both the direction and the degree of the impact may vary with spatial and temporal change. Therefore, the relationship between urbanization and agricultural TFP may not be limited to a linear one. In addition, these influences of urbanization on agricultural TFP not only take place in one region but are also related to neighborhoods from the spatial perspective. Therefore, this paper argues that urbanization has both a “siphon effect” and “trickle effect” on agricultural TFP by using spatial econometric model to identify spatial spillover effect [
45,
46,
47,
48].
However, it seems that there is little literature about the U-shaped relationship verification between urbanization and agricultural TFP in China from the spatial perspective. According to the above theoretical analysis, this paper aims at filling the gap of identifying the impact of urbanization on agricultural TFP from the perspective of space. Further, this paper puts forward the hypothesis that the impact of urbanization on agricultural TFP may present a U-shaped curve relationship. In this paper, urbanization which affects agricultural TFP is defined as a core explanatory variable. The U-shaped curve relationship between urbanization and agricultural TFP may exist. In addition, the spatial direct effect, indirect effect, and total effect of urbanization will be analyzed.
In the first stage of urbanization, before the arrival of the “inflection point”, the urbanization development level is relatively low, and the speed is fast. The rapid expansion of cities requires lots of high-quality labor, farmland and investment from rural areas. Therefore, the impact of urbanization on agricultural TFP growth may be negative. In the second stage of urbanization, after the arrival of the “inflection point”, the development level of urbanization in this stage is relatively high, and more attention will be paid to the development quality of urbanization rather than the development speed of urbanization. A large amount of investment, advanced technology and high-quality human capital from cities will be invested in rural areas. Therefore, at this stage, urbanization will improve the resource allocation efficiency and agricultural TFP.
5. Conclusions and Recommendations
5.1. Conclusions
From 2004 to 2016, the average annual growth rate of agricultural TFP in China is 4.8%. It indicates that the growth of agricultural TFP may contribute to the enhancement of agriculture. Agricultural technological progress is one of the main forces to promote the growth of agricultural TFP in China, but scale efficiency index and technical efficiency index may restrain the growth of agricultural TFP to the extent.
At present, China’s urbanization development and agricultural TFP growth have strong spatial spillover effects, and the spatial correlation effect is positive. The U-shaped curve of urbanization influencing the growth of agricultural TFP is significant on the direct effect, indirect effect, and total effect. This illustrates the impact and the degree of urbanization on agricultural TFP presents the dynamic change trend with the development stage of urbanization. Meanwhile, both the increase in R&D expenditure and the marketization degree are also important factors to promote the growth of agricultural TFP.
From the regional level of eastern, central and western regions, the impact of urbanization on agricultural TFP varies greatly in different regions due to the influence of economic development level, resource factor endowment and human geography factors.
5.2. Recommendations
A new pathway of urbanization should be followed. The Chinese government attaches great importance to the guiding role of urbanization in agricultural upgradation and takes measures such as absorbing surplus rural labor through urbanization, promoting the large-scale operation of agriculture, increasing policy support for agriculture to accelerate the modernization of agricultural production, which are conducive to the coordination of urbanization and modern agriculture.
While paying attention to the speed of urbanization development, the government should pay more attention to the quality of urbanization. From the perspective of sustainable coordination of urbanization and agricultural production, the siphon effect of urban on agriculture should be offset, while the “trickle-down effect” of cities on the agricultural sector should be made full use of. Advanced science and technology, capital investment and efficient management experience in cities should be applied to agricultural production. The construction of agricultural infrastructure and the supply of agricultural input factors are guaranteed to the greatest extent, so as to ensure sustainable growth of agricultural TFP.