2.3.3. Analysis of the Coupling and Coordination Relationships among Various Sub-Functions of Cultivated Land

A coupling–coordination-degree model was introduced to quantitatively analyze the interactions among various functions of cultivated land and the degree of coupling and coordination among them. Coupling is a physical concept that can describe the strength of an interaction between two or more systems or motions, but it cannot characterize the level of cooperation among systems. The coordination degree makes up for this deficiency by measuring the level of coordinated development among the systems. It is widely used in studies of system relationships among land, economy, and society [37]. The specific steps used were as detailed below.

Step 1: Measure the coupling degree. After standardizing the data, the coupling– coordination degree was measured as:

$$\mathbf{C}\_{t} = \sqrt[n]{\prod\_{i=1}^{n} \mathbf{Y}\_{m} / \left(\sum\_{i=1}^{n} \mathbf{Y}\_{m}\right)^{n}} \tag{6}$$

where *C<sup>t</sup>* is the coupling degree in year *t*. With 0 ≤ *C<sup>t</sup>* ≤ 1, the closer the value is to 1, the stronger the interaction between systems is, while the converse is true. *Y<sup>m</sup>* is the comprehensive score of system *m*, and *n* is the number of subsystems. When the relationship among three systems is measured, *n* = 3, and when the relationship between two subsystems is measured, *n* = 2.

Step 2: Measure the coordination index:

$$T = \sum\_{i=1}^{n} \mathfrak{a}\_{i} Y\_{m\prime} \sum\_{i=1}^{n} \mathfrak{a}\_{i} = 1 \tag{7}$$

where *T* is the coordination index and *α<sup>i</sup>* is the weight of subsystem *i*. When measuring the coupling–coordination degree of each subsystem, the entropy-weight method was used to calculate the weight of each index, and the weight was then calculated [36].

Step 3: Measure the coupling–coordination degree:

$$D = \sqrt{\mathbb{C} \times T} \tag{8}$$

where *D* is the coupling–coordination degree. The higher the coupling–coordination score is, the better the coupling–coordination relationship between the two systems is.

2.3.4. Analysis of the Key Drivers of Multi-Functionality of Cultivated Land

A change in the functionality of cultivated land represents a part of a large, complex system, and the factors influencing cultivated-land evolution during different developmental stages and different regions vary. Development processes, urban construction, and policies are jointly affected, and each factor has a variable degree of influence. To examine the breadbasket regions in Jilin Province, 18 influencing factors were chosen, as shown in Table 3.

Based on the multi-functional evaluation of cultivated land, the key factors affecting change in multi-functionality were identified using Geodetector, a statistical method that detects spatial heterogeneity and reveals the drivers behind it [38]. The strengths of the driving factors were determined following the method by Wang and Xu [39].

**Table 3.** Definition of factors influencing the multi-functionality of cultivated land. The per capita construction-land standard in rural areas was 150 m2/person, and the urban per capita constructionland standard was 120 m2/person. The average weighting method was used to measure the overall pressure; the management and control levels of permanent basic farmland, prohibited construction areas, restricted construction areas, conditional construction areas, and permitted construction areas in the agricultural-policy zoning decreased in order, and were assigned values of 5, 4, 3, 2, and 1, respectively, in the calculations. Because of data limitations in 1990 and 2000, Jilin Province did not produced agricultural-land-grading data; the average grain yield was used to correct the cultivated-land utilization to obtain graded data for the corresponding years.


#### **3. Results**

*3.1. Spatiotemporal Variation in and Main Obstacles to the Multi-Functionality of Cultivated Land* 3.1.1. Temporal Variation in the Multi-Functionality of Cultivated Land

The evaluation, degree of change, and coefficient of variation of each function of cultivated land during different periods in the breadbasket regions are shown in Table 4. The average multi-functional scores for cultivated land for the four research time nodes were 0.222 (1990), 0.227 (2000), 0.361 (2010), and 0.451 (2020), representing an increase of 102.92% during the 30 years from 1990 to 2020. Although the overall multi-functional level of cultivated land was not high, the increase was large with clearly differentiated phases, showing a trend from basically unchanged to rapid improvement to steady increase. The economic sub-function increased the most, from 0.148 in 1990 to 0.484 in 2020, an increase of 227.51%. The social function was second, with an increase of 152.69%, from 0.159 in 1990 to 0.401 in 2020. The ecological function was almost stagnant, with current levels comparable to those of 30 years ago, only rising from 0.441 in 1990 to 0.456 in 2020. The rapid improvement in the economic and social functions of cultivated land in the breadbaskets

led to an increase in the level of multi-functionality, to which the ecological function did not contribute.

**Table 4.** Trends in multi-functional changes in cultivated land in the black-soil breadbaskets of Jilin Province, Northeast China, from 1990 to 2020.


#### 3.1.2. Spatial Variation and Differentiation in the Multi-Functionality of Cultivated Land

There were obvious and significant spatial differences in the multi-functionality and sub-functions of cultivated land in the 28 breadbaskets. The coefficient of variation of the ecological functions was the largest, showing a continuous increase over the past 30 years, from 0.368 in 1990 to 0.450 in 2020 (Table 4), indicating that the ecological functions of cultivated land varied among different breadbaskets. the differences in time-progressed ecological functions were more pronounced than those in other functions.

The spatial differences in the social function of cultivated land were also obvious but to a lesser extent than the ecological function. The coefficient of variation dropped from 0.338 in 1990 to 0.332 in 2020, indicating little overall change, although there were some differences. The differences in the economic function of cultivated land were the smallest compared with the other functions, with the average coefficient of variation decreasing from 0.267 in 1990 to 0.252 in 2020, indicating that the economic attributes of cultivated land were well balanced among the breadbaskets.

Based on the current multi-functionality of cultivated land and the changes recorded over the last 30 years, although the multi-functionality increased, it showed an unbalanced development of the Matthew effect, i.e., higher levels of multi-functionality led to higher levels, while lower levels led to yet lower levels. The range of the multi-functionality and sub-functions of cultivated land among the breadbaskets significantly increased, showing an overall increase of 220%, with the range in economic and social functions increasing by more than 300%. Even the much weaker ecological function also expanded by 12%. Overall, the use of cultivated land over the last 30 years increased the spatial differences in multi-functional utilization to an exaggerated degree. This directly reflects the lack of the consideration of cultivated-land functions in cultivated-land protection (Figures 3 and 4). In addition, the changes in the ecological functions of cultivated land were polarized (Figure 3c) between the east and the west (Figure 4c). On average, the former (with a sum score of about 9.108) had a value about three times that of the latter (sum score of about 3.674) (Figure 3c).

#### 3.1.3. The Main Obstacles to Multi-Functionality of Cultivated Land

The obstacle degree was calculated with the evaluation index for the four time nodes for each breadbasket to determine what factors were limiting the functions of cultivated land. Over the last 30 years, the economic function of cultivated land restricted the multifunctionality of cultivated land the most, followed by the social function and then the ecological function (Table 5). However, the dominant restrictive effect of the economic function weakened (from 13.46 in 1990 to 11.56 in 2020), while the restrictive effect of the ecological function increased (from 4.78 in 1990 to 6.56 in 2020, a rise of 37.24%). This suggests that how the ecological function is managed in the future could be the key to improving the functions of cultivated land. After sorting the index obstacle scores for the breadbaskets, the per capita agricultural output, the degree of agricultural mechanization, the average output of cultivated land, and the agricultural-labor productivity had the strongest restrictive effects on the functions of cultivated land. However, based on the changes in the index values, the per capita agricultural output showed a decreasing trend

(from 4.29 in 1990 to 3.63 in 2020), and the degree of agricultural mechanization may soon become the biggest obstacle. Barriers to national contribution and effective irrigation are rising, highlighting the fact that attention must be paid to the multi-functional utilization of cultivated land in the future. *Land* **2022**, *11*, x FOR PEER REVIEW 11 of 19 *Land* **2022**, *11*, x FOR PEER REVIEW 11 of 19

**Figure 3.** Multi-functional composition of cultivated land in 28 black-soil breadbaskets, Jilin Province, Northeast China, from 1990 to 2020. (**a**) Economic function. (**b**) Social function. (**c**) Ecological function. (**d**) Multi-function. **Figure 3.** Multi-functional composition of cultivated land in 28 black-soil breadbaskets, Jilin Province, Northeast China, from 1990 to 2020. (**a**) Economic function. (**b**) Social function. (**c**) Ecological function. (**d**) Multi-function. **Figure 3.** Multi-functional composition of cultivated land in 28 black-soil breadbaskets, Jilin Province, Northeast China, from 1990 to 2020. (**a**) Economic function. (**b**) Social function. (**c**) Ecological function. (**d**) Multi-function.

**Figure 4.** Changes in function of cultivated land in the black-soil breadbaskets of Jilin Province, Northeast China, from 1990 to 2020. (**a**) Economic function. (**b**) Social function. (**c**) Ecological function. (**d**) Multi-function. **Figure 4.** Changes in function of cultivated land in the black-soil breadbaskets of Jilin Province, Northeast China, from 1990 to 2020. (**a**) Economic function. (**b**) Social function. (**c**) Ecological function. (**d**) Multi-function. **Figure 4.** Changes in function of cultivated land in the black-soil breadbaskets of Jilin Province, Northeast China, from 1990 to 2020. (**a**) Economic function. (**b**) Social function. (**c**) Ecological function. (**d**) Multi-function.

The obstacle degree was calculated with the evaluation index for the four time nodes for each breadbasket to determine what factors were limiting the functions of cultivated land. Over the last 30 years, the economic function of cultivated land restricted the multi-

3.1.3. The Main Obstacles to Multi-Functionality of Cultivated Land

The obstacle degree was calculated with the evaluation index for the four time nodes for each breadbasket to determine what factors were limiting the functions of cultivated land. Over the last 30 years, the economic function of cultivated land restricted the multi-

ecological function (Table 5). However, the dominant restrictive effect of the economic

ecological function (Table 5). However, the dominant restrictive effect of the economic

3.1.3. The Main Obstacles to Multi-Functionality of Cultivated Land


**Table 5.** Calculated obstacle degrees for factors influencing cultivated-land functions in the black-soil breadbaskets of Jilin Province, Northeast China, from 1990 to 2020.

#### *3.2. Coupling and Coordination Relationships among Various Sub-Functions of Cultivated Land*

A coupling–coordination degree model was used to compare the sub-functions of cultivated land in the breadbaskets from 1990 to 2020 and was divided into 10 levels (Figure 5). The degree of coupling–coordination among various functions of cultivated land showed an overall upward trend, from "low coupling coordination–antagonistic coupling coordination" to "high coupling coordination–optimal coupling coordination". Nine breadbaskets in eastern Jilin with low levels of coupling–coordination all improved over time, reaching antagonistic coupling–coordination or even high coupling–coordination. Nineteen breadbaskets in central and western Jilin Province all attained a high degree and optimal level of coupling and coordination. Among them, Lishu County and Zhenlai County achieved good coupling–coordination, but no breadbasket reached high-quality coupling–coordination. From 1990 to 2000, overall, the coupling–coordination degree of the multi-functional value of cultivated land remained at a low level, and in fact, the coupling– coordination degree for Gongzhuling City, Yongji County, Qian'an County, Changling County, and Da'an City all declined. During the 20-year period between 2000 and 2020, the coupling and coordination degree of the multi-functional value of cultivated land did improve, although the increase was generally faster in the western region than the eastern region.

#### *3.3. Key Factors Influencing the Multi-Functionality of Cultivated Land*

Figure 6 and Table 6 rank the driving factors affecting the multi-functionality of cultivated land in the 28 breadbaskets at the four time nodes. In general, physical and geographical factors were the main factors influencing the multi-functional changes in cultivated land, while the influence of economic factors showed a sharp downward trend over the 30 years (the total *q*-value decreased from 1.55 in 1990 to 0.92 in 2020). However, urban construction and policy factors had very limited effects on the changes in multifunctionality. The factors that had a greater impact in 1990 were the quality of cultivated land and the proportion of secondary and tertiary industries. In 2000, the pressure of construction land, annual precipitation, and proportion of built-up area began to have a greater impact on the multi-functionality of cultivated land. From 2010, the quality of cultivated land and proportion of secondary and tertiary industries once again dominated the changes in multi-functionality. Annual precipitation and elevation in 2020 were particularly important for cultivated-land multi-functionality.

Physical geography

Economic development

Urban construction

Policy

**Figure 5.** Coupling–coordination among sub-functions of cultivated land in the black-soil breadbaskets of Jilin Province, Northeast China, from 1990 to 2020. Data from Wang et al. [40] were used to divide the coupling–coordination degree into 10 types. **Figure 5.** Coupling–coordination among sub-functions of cultivated land in the black-soil breadbaskets of Jilin Province, Northeast China, from 1990 to 2020. Data from Wang et al. [40] were used to divide the coupling–coordination degree into 10 types. *Land* **2022**, *11*, x FOR PEER REVIEW 14 of 19

**Figure 6.** Impact scores for multi-functional factors affecting cultivated land in the black-soil breadbaskets of Jilin Province, Northeast China, from 1990 to 2020. The meanings of the abbreviations used in the figures are shown in Table 3. **Figure 6.** Impact scores for multi-functional factors affecting cultivated land in the black-soil breadbaskets of Jilin Province, Northeast China, from 1990 to 2020. The meanings of the abbreviations used in the figures are shown in Table 3.

**Table 6.** Indicator values for factors influencing the multi-functionality of cultivated land in the

Elevation 0.54 0.62 0.56 0.65 0.59 Slope 0.01 0.01 0.01 0.00 0.01 Annual precipitation 0.55 0.75 0.48 0.66 0.61 Distance from major rivers 0.11 0.11 0.06 0.03 0.08 Cultivated-land quality 0.76 0.31 0.78 0.54 0.59 Distance from provincial capital 0.54 0.57 0.47 0.26 0.46 Distance from central city 0.38 0.37 0.47 0.28 0.37

Subtotal 2.88 2.73 2.81 2.42 2.71

industries 0.71 0.50 0.63 0.30 0.53 Subtotal 1.55 1.23 1.44 0.81 1.26

culture 0.26 0.48 0.20 0.20 0.28 Subtotal 1.11 2.07 1.39 1.00 1.39

For the mismatch between the supply and demand of multi-functional cultivated land, proper interference and regulation are needed [41]. Implementing smaller-scale land-use management or land-use planning is often more efficient in solving the problem

Per capita GDP 0.34 0.31 0.37 0.24 0.32

Fixed asset investment per land 0.31 0.64 0.48 0.59 0.50 Urbanization rate 0.64 0.63 0.37 0.41 0.51 Population density 0.65 0.60 0.41 0.29 0.49 Subtotal 1.60 1.86 1.26 1.29 1.50

Percentage of built-up area 0.27 0.65 0.43 0.30 0.41 Road-network density 0.14 0.10 0.22 0.17 0.16 Agricultural-policy division 0.04 0.05 0.03 0.02 0.03 Construction-land-pressure index 0.40 0.79 0.51 0.31 0.50

*4.1. Policy Suggestions for Multi-Functional Management of Cultivated Land* 

black-soil breadbaskets of Jilin Province, Northeast China, from 1990 to 2020.

**Factor Indicator 1990 2000 2010 2020 Average** 

Per capita agricultural output of farmers

Proportion of secondary and tertiary

Proportion of financial support to agri-

**4. Discussion** 


**Table 6.** Indicator values for factors influencing the multi-functionality of cultivated land in the black-soil breadbaskets of Jilin Province, Northeast China, from 1990 to 2020.

#### **4. Discussion**

#### *4.1. Policy Suggestions for Multi-Functional Management of Cultivated Land*

For the mismatch between the supply and demand of multi-functional cultivated land, proper interference and regulation are needed [41]. Implementing smaller-scale land-use management or land-use planning is often more efficient in solving the problem and at a low cost [42]. This research study deepened our understanding of the function of cultivated land and can inform policies for the long-term protection of cultivated land. The results of this study are applicable not only to Northeast China but also to other major grain-producing areas that are under pressure to protect cultivated land.

Incorporating multi-functional utilization into policy considerations for cultivatedland management can help balance differences in cultivated-land functions among regions. Research on cultivated-land protection has a long history and has received special attention in recent years [43], especially in the context of prominent global land-use contradictions and serious threats to food security [44]. However, the protection of cultivated-land quantity, quality, productivity, etc., has perhaps been overemphasized [45], while the sustainability of cultivated-land use has received less attention, although it has started to come into focus [46,47], and the relatively hidden multi-functional attributes of cultivated land have rarely been considered. Differences in the use of cultivated land often lead to differences in management policies, which ultimately affect the future sustainability of land use. The multi-functional imbalance of cultivated land in the 28 breadbaskets studied here highlights the need to address this issue. A regional imbalance results in a lack of drive for cultivated-land protection. The direction and perception of cultivated-land protection need to change towards using the sustainable protection and utilization of cultivated land as a starting point for cultivated-land management, and to integrate multi-functionality into the formulation of cultivated-land-management policies and planning.

The multi-functional value of cultivated land needs to be demonstrated, and sufficient compensation offered, to encourage cultivated-land protection. The economic benefits of growing grain on cultivated land are relatively low, and the comparative benefits of growing grain are likely to continue to decrease with the development of economy and society. When the income of agricultural production is unbalanced, the government can improve and protect farmers through subsidy programs [48]. However, without reasonable compensation for multi-functional land use, there is no incentive for farmers to protect the land [49]. Obstacles to multi-functionality compound the problem. Among the four main obstacles to multi-functionality of cultivated land in the studied breadbaskets, the per capita agricultural output and the average output of cultivated land were directly related to the income level generated by cultivating land, while the other two barriers, agriculturallabor productivity and agricultural mechanization, were highly correlated with the level of economic income from cultivated land. These indicators can only improve if income levels are high enough. Currently, farmers are presented with a stark choice between protecting the land and remaining on lower incomes or giving up the land and moving to cities to achieve higher incomes. The government needs to take effective measures to recalibrate the value of cultivated-land resources, highlighting the multi-functional value of cultivated land, and give farmers proper compensation for land protection.

The ecological utilization of cultivated land in breadbaskets needs to be improved and the long-term sustainable utilization of cultivated land needs to be promoted. Ecological issues with cultivated land are closely related to the presence of people, compared with other natural resources, because of the long history of human settlement around areas of cultivation [50]. People benefit directly from the positive effects of cultivation, such as environmental improvement and biodiversity, but there are also negative effects, such as water pollution and straw-burning pollution [51]. The ecological function of breadbaskets has not been improved for many years, and this has increasingly restricted the multifunctionality of cultivated land. At a time when global ecological security is under threat, effective measures should be taken to curb negative trends, and the future ecological utilization of cultivated land is necessary. When considering the cultivated-land output, recycling and reducing the use of pesticides, fertilizers, herbicides, etc., should be promoted to save production costs and improve agro-ecological benefits.

#### *4.2. Limitations and Future Research*

Based on long-term research, we analyzed the unbalanced state of the multi-functionality of cultivated land and gave a feasible solution to balance the multi-functionality of cultivated land. However, with the continuous emergence of global ecological threats and the rapid urbanization of agricultural areas, the multi-functional utilization of cultivated land still requires further attention and more in-depth research, and our study still has two important limitations that need to be addressed [52].

The evaluation criteria used to assess the multi-functionality of cultivated land at different research scales are different, and policy formulation needs to be adjusted accordingly. The multi-functional mismatch of cultivated land is multi-scaled, and the analysis of different scales is an important method to determine the reasons for this mismatch between supply and demand [53]. Based on the scales being considered, relevant indicators for evaluation need to be selected [31]. As a county-level study, this research study addresses problems in county-level farmland protection policies, and can suggest countermeasures, but it is difficult to extrapolate the results to larger or smaller study areas. For example, understanding the imbalance of cultivated-land functions among regions and taking corresponding measures require the evaluation of the functions of cultivated land at a national level. Conversely, engineering and utilization measures to improve the function of cultivated land need to be considered at a plot scale. Evaluation forms the basis for policy-making, and the choice of indicators forms the basis for evaluation [54]. Therefore, in future research at different scales, different evaluation-index systems should be selected according to local conditions, to make the results more robust.

The functions of cultivated land represent a large, complex system, and it is difficult to describe all the relevant aspects of cultivated land with the existing macro data. The functions of cultivated land are intertwined with economic, social, and ecological systems, and macro-statistical data and geographic data can only reflect the overall functions of cultivated land to a certain extent. The different scales and standards of the statistical data used are also likely to cause discrepancies between evaluation results and empirical data. To eliminate such errors, data encompassing as many perspectives as possible need to be

collated [55]. For example, regarding the ecological function of cultivated land, the level of farmland pollution may be affected by factors such as straw burning, agricultural nonpoint source pollution, and plastic pollution [56]. These indicators may require additional investigation and research at a micro level. Equally, extrapolating policy recommendations from cultivated-land utilization through research on multi-functionality and facilitating farmers in recognizing the multi-functionality of cultivated land are topics worthy of long-term research.

#### **5. Conclusions**

Multi-functionality is an objective attribute of cultivated land that influences the sustainability of cultivated-land utilization and the long-term protection of cultivated land. To date, the importance of black-soil cultivation and protection has not received sufficient attention because of an overemphasis on grain output. An effective way of addressing this situation is to understand the changes in the multi-functionality of cultivated land and identify the key driving and limiting factors behind any changes. We used an improved TOPSIS model to measure the temporal and spatial variation in the cultivated-land functions over 30 years, from 1990 to 2020, in 28 breadbaskets in Jilin Province, Northeast China. The key driving factors behind and major obstacles to cultivated-land functions were determined using an obstacle degree model and a geographic detector model. The coupling and coordination relationships among the various functions of cultivated land were also analyzed. Suggestions are made to help improve future land-management policies. This study provides a baseline for the multi-functional utilization of cultivated land and the long-term protection of cultivated land in China and even in the world's major grain-producing regions and expands the perspective of cultivated-land protection.

The multi-functionality of cultivated land in the breadbaskets increased significantly in the 30 years from 1990 to 2020 (by 102.92%). Whether a function is used to its full potential is an important limiting factor for cultivated-land utilization, and the ecological function of cultivated land is likely to be more important in the future. There was an obvious spatial differentiation in cultivated-land functions across the breadbaskets; this difference was the largest for the ecological function, followed by the social function, and was the smallest for the economic function. The coupling–coordination degree for each sub-function generally showed an upward trend, but there was again an obvious spatial differentiation. The multi-functionality of cultivated land in the breadbaskets presented an unbalanced growth trend. In addition, the sub-functions of cultivated land were not well coordinated, leading to an imbalance in promoting cultivated-land protection. Cultivated-land protection in this region over the last 30 years also exacerbated social inequality. The government must intervene with effective measures, especially in the processes of cultivated-land utilization and management, and the multi-functionality of cultivated land should be taken as a starting point for formulating policies. The multi-functional value of cultivated land needs to be evaluated, and farmers should be offered reasonable compensation to reduce the imbalance and differences in cultivated-land functions among regions and improve farmers' enthusiasm for cultivated-land protection. The ecological utilization of cultivated land in breadbaskets should be improved and sustainable utilization should be promoted.

**Author Contributions:** H.G., Conceptualization, Methodology, Software, Formal analysis, Visualization, Investigation, and Writing—original draft; L.C. and Y.L. (Ying Li), Methodology and Writing—review and editing; G.L., Formal analysis and Data curation; Z.Z., Visualization and Validation. Y.L. (Yuefen Li), Conceptualization, Supervision, Funding acquisition, and Writing—review and editing. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was supported by National Natural Science Foundation of China (grant No. 42177447) and Science and Technology Development Plan Project of Jilin Province (grant No. 20210203010SF).

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

**Informed Consent Statement:** Not applicable.

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

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