Sustainable Utilization of Agricultural Land in Chengdu Metropolitan Area Based on Emergy Analysis

Kai LAN, Qinghong RAN

1. School of History & Geography and Tourism, Chengdu Normal University, Chengdu 611130, China; 2. China West Normal University, Nanchong 637000, China

Abstract [Objectives] This study aimed to analyze the sustainable use of agricultural land in the Chengdu metropolitan area from 2006 to 2016. [Methods] Using Odum’s emergy theory, an index system was constructed to evaluate the sustainable use of agricultural land, including total emergy input-output ratio, industrial emergy input-output ratio, environmental load index and sustainable use index of agricultural land based on emergy, to reflect the sustainable use of agricultural land in the Chengdu metropolitan area. The data base was a unified standard that was converted from various types of energy stored and flowing in the agricultural land system of the Chengdu metropolitan area, that is, emergy. [Results] From 2006 to 2016, the total emergy input-output ratio of agricultural land in the metropolitan area fluctuated and decreased, lower than the national average. The industrial emergy input-output ratio was generally in a fluctuating downward trend. The environmental load index of agricultural land in the metropolitan area was lower than the national average. However, it has been on the rise since 2012. During the corresponding period, the sustainable use index of the region also showed a downward trend. [Conclusions] The utilization rate of emergy in this area was low. The dependence of industrial emergy input-output ratio on industrial subsidiary energy and the degree of agricultural mechanization are constantly improving. The environmental resources in this area still have room for accommodation and have not been fully utilized. The sustainable use of agricultural land has been declining.

Key words Agricultural land, Emergy analysis, Sustainable use, Chengdu metropolitan area

1 Introduction

Agricultural land is land directly used for agricultural production. It is an important resource element of life and production. With the increase in population and the rapid expansion of industry and cities, the limited land resources, especially the area of agricultural land, continue to decrease. In addition, the irrational use of agricultural land by humans has exacerbated the scarcity of land. Human activities have greatly changed the natural ecosystem, making a significant change in the appearance of the natural environment, in which the change of agricultural land cover is particularly significant. Therefore, research on the sustainable utilization of agricultural land resources is of great significance to the sustainable utilization of land and food production safety in China. Currently, many different research methods have been used from different perspectives, such as farmers’ concurrent business and circular economy, and methods used are emerging in endlessly, including ecological footprint method, entropy method, and so on. These research methods have a common shortcoming: they are all based on different levels of systems and dimensional data, so they cannot be compared and accumulated. In this study, emergy analysis method was adopted to analyze the agricultural land in Chengdu metropolitan area and evaluate the sustainable use of the agricultural land.

2 Overview of study area

The Chengdu metropolitan area is centered on Chengdu City, and surrounded by Deyang, Ziyang and Meishan, which form a large metropolitan area (Fig.1a). This area is located in the central part of Sichuan Province (Fig.1b), and on the western edge of the Sichuan Basin. The terrain is high in the northwest and low in the southeast, dominated by hills and mountains, with an average altitude of 1 000-3 000 m. It belongs to the heartland of Chengdu Plain[1]. Due to the rainy weather in this area, there is less sunshine. The average annual sunshine duration is 1 000-1 300 h[2]. The annual average temperature is 16.1 ℃.

Fig.1 Schematic diagram and location map of Chengdu metropolitan area

The total land area of the Chengdu metropolitan area is about 3 318 900 ha (Table 1). As of 2016, the area of cultivated land is 1 341 400 ha, the permanent population was 26.5 million, and the average urbanization rate was about 53%[3]. This area is the main production base of agricultural products such as grain and vegetables in Sichuan Province. The sown area of grain is about 1 478 000 ha, and the total grain output is 8 178 000 t. In 2016, the GDP of the entire region was about 1 598.3 billion yuan.

Table 1 Overview of Chengdu metropolitan area

3 Methods and analysis

3.1 Methods

3.1.1Theoretical introduction. According toEmergyAnalysisofEco-economicSystem, the term emergy refers to a certain amount of effective energy directly and indirectly needed to form a certain product or labor service, and its unit is emjoules. The theory and method of emergy analysis were founded by H.T. Odum, a famous American ecologist and the father of system ecology[4]. Due to the fundamental difference in quality and value, different types of energy can’t be added, subtracted and compared. In the 1980s, emergy theory, concept and analysis method have emerged internationally. This research method can convert different energies and materials within the ecological economic system, so as to become the standard consistent emergy. Thus, different types of energy can be compared and measured. Since any energy is originally derived from solar energy, in the actual application process, "solar energy" is used to measure the emergy of a certain energy[5]. Any type of energy can be measured on the basis of solar energy, and its unit is solar emjoules (sej).

3.1.2Data sources and methods. The original data of the study comes from the statistical yearbook. The data objects are mainly agricultural land in the area (including arable land, garden land, woodland, pasture and fish ponds,etc.). According to the structure of the area, the emergy input and output of agricultural land were determined. The input part can be divided into three parts: natural, industrial and bio-energy[6]. Natural energy includes solar energy, wind energy, rain potential energy,etc. Industrial energy includes chemical fertilizers, pesticides, agricultural film, electricity, gas, diesel,etc. Bio-energy includes manpower and organic fertilizer. The output is mainly divided into five categories: food crops, cash crops, forestry products, livestock and poultry products, and aquatic products. According to Chen Fu’sAgriculturalEcology, the original input and output data were converted into energy values. Then, according to Lan Shengfang’sEmergyAnalysisofEco-economicSystem, the energy data were converted into emergy. Thus, the emergy of agricultural land input and output in Chengdu metropolitan area from 2006 to 2016 was obtained[7].

3.1.3Establishment of an evaluation system. Based on the emergy data of agricultural land input and output in the Chengdu metropolitan area, according to the emergy analysis method in Lan Shengfang’sEmergyAnalysisofEco-economicSystem, a land use situation index system was constructed to obtain the judgment index of sustainable land use. The index system is divided into two major items, single emergy indices and comprehensive emergy indices (Table 2).

Table 2 Evaluation system for sustainable utilization of agricultural land in Chengdu metropolitan area

3.2 Analysis

3.2.1Emergy input of agricultural land in Chengdu metropolitan area. During 2006-2016, the total emergy investment of agricultural land in the Chengdu metropolitan area showed an upward trend overall, and during 2006-2012, it was in a state of fluctuation. Since 2012, the emergy input was 1.556×1023sej, and in 2016, it increased to 1.759×1023sej. The types of emergy input for agricultural land in this area were divided into four categories: renewable environmental resource emergy, non-renewable environmental resource emergy, non-renewable industrial subsidiary emergy, and renewable organic emergy (Table 3). The results show that over the years, non-renewable industrial subsidiary emergy accounted for about 85% of the total input emergy, while renewable environmental resource emergy accounted for a relatively small proportion, indicating high degree of agricultural intensification and weak dependence on nature in the metropolitan area, conducive to the development of modern agriculture in the area.

Among various emergy inputs, renewable environmental resource emergy showed a downward trend year by year, from 1.295×1022sej in 2006 to 1.167×1022sej in 2016, with a decrease of about 9.9%. This was mainly due to the gradual decrease in annual precipitation in the area. This type of emergy input dropped overall, suggesting that the dependence of agricultural development on nature in the area was gradually decreasing.

In addition, only the net loss of topsoil was considered in the emergy input of non-renewable environmental resources. The overall fluctuation was relatively small, with a slight decrease. As the relevant departments have paid more attention to water and soil conservation, as well as ecological protection of agricultural land and water and soil management in recent years, the ecological environment has been improved to a certain extent, and the amount of topsoil loss has decreased. Another non-renewable resource, industrial subsidiary emergy input, showed an upward trend overall, from 1.359×1023sej in 2006 to 1.511×1023sej in 2016, with an increase of about 11.2% (Table 3). The input of diesel, total power of agricultural machinery and electricity was increasing year by year, indicating that the level of agricultural mechanization in this area is continuously improving. However, these types of emergy inputs accounted for a small proportion of non-renewable industrial subsidiary emergy, so their changes had little effect on the change trend of industrial subsidiary emergy input.

Table 3 Emergy input of agricultural land in Chengdu metropolitan area during 2006-2016 sej

3.2.2Emergy output of agricultural land in Chengdu metropolitan area. The output of agricultural land in the Chengdu metropolitan area mainly includes planting and livestock breeding products. Among them, the output of planting industry accounted for more than 35% of the total. The output of livestock breeding accounted for more than 40%. The two together accounted for about 80%, reaching 90% in some years (Table 4). The overall emergy output in the area showed a downward trend, from 1.881×1023sej in 2006 to 1.538×1023sej in 2016. The decrease was about 18%. During this period, the obvious point of decline appeared in 2008. This might be due to the reduced production of agricultural products caused by the rare snow disaster in 2008. After that, agricultural output rebounded in a short period of time, but then there was a continuous decline. During the corresponding period of time, the area of agricultural land in this area had been decreasing year by year, and the area of land for secondary and tertiary industries and urban construction had been increasing year by year. The total sown area of crops was in a downward trend, from 2 412 880 ha in 2006 to 2 319 910 ha in 2016. This is one of the important reasons for the decrease in emergy output of agricultural land in this area. Although the emergy output of the planting industry was increasing, it benefits from the promotion of high-yield seeds. The emergy output of the livestock breeding industry in this area was in a declining trend, mainly manifested in the emergy output of meat, from 10.975×1022sej in 2006 to 6.622×1022sej in 2016. The decrease was about 40%. The reason is that the development of the livestock breeding industry requires a vast area; but the level of modernization in the metropolitan areas is relatively high, and the cost of land continues to rise. Based on income consideration, it is transferred to a relatively backward economic area. As a result, the emergy output of meat has declined. In the output emergy of planting industry, the emergy output of food crops (including rice, wheat, corn, beans and potatoes) accounted for about 60%, the emergy output of oil crops accounted for about 30%, and the emergy output of vegetables and fruits accounted for about 5%. It can be seen that the planting industry structure in this area is relatively simple. Between 2006 and 2016, the output of food crops had not changed much and was in a state of gentle fluctuation, but the output of economic crops, especially oilseeds, vegetables, fruits and tea was constantly increasing, reflecting that the planting industry structure is adjusted, and the planting industry has been significantly optimized[8].

The planting industry and livestock breeding industry in the Chengdu metropolitan area accounted for more than 80%, but the sum of forestry and fishery output accounted for less than 1%, reflecting the single structure of agricultural output in the area. The structure was dominated by food crops, of which the proportion was relatively large, while the proportion of cash crops is relatively small, resulting in low agricultural economic benefits. Therefore, the area should optimize the structure of crops and increase the types of crops, especially the cultivation of cash crops to increase the value of agricultural production. This is the development direction of modern agriculture. But the economy of this metropolitan area was not dominated by agriculture, of which the proportion in the national economy was decreasing year by year. As of 2016, the proportion of agricultural output value was only 6%. Therefore, the area should optimize the agricultural structure, improve intensification and quality of agricultural products, and provide raw materials and space resources for other industries while ensuring food security.

3.2.3Evaluation indices for emergy of agricultural land in Chengdu metropolitan area. Based on the data on the emergy input and output of agricultural land from 2006 to 2016, the results were calculated according to the formula in Table 2 to comprehensively evaluate the sustainable use of agricultural land in the metropolitan area[9], and the results are listed in Table 5. They are mainly emergy indices for sustainable use of agricultural land, including total emergy input-output ratio (EIR), industrial emergy input-output ratio (IEIR), land environmental load index (ELR), and land sustainable use index (ESI).

The total emergy input-output ratio of agricultural land in the Chengdu metropolitan area fluctuated and declined between 0.947 and 1.241 (Fig.2). It reached the lowest value of 0.947 in 2008. The main reason was the Wenchuan earthquake and the severe snow disaster in 2008. In addition, the average total emergy input-output ratio of agricultural land in the metropolitan area from 2006 to 2016 was 1.066, lower than the national average total emergy input-output ratio of agricultural land in 2015[10]. This set of data shows that the utilization efficiency of agricultural land in the Chengdu metropolitan area is low, lower than the national average level of land use efficiency and in a trend of declining fluctuation. The main reason for this situation is that from 2006 to 2016, emergy input in this area was rising, while emergy output was not increased. On the contrary, it was in a downward trend, which was reflected in the high input and low income in agricultural production. Although the level of agricultural mechanization in the metropolitan area was constantly improving and the emergy output of the planting industry was increased significantly, with the increase in land prices, the cost of livestock breeding had skyrocketed, leading to the shift of livestock breeding to areas with lower development costs and the significant decrease in emergy output of the livestock breeding industry. As the newly increased investment was applied to the relatively low-efficiency planting industry and the high-efficiency livestock breeding industry was relocated, the emergy input rose continuously, and the emergy output decreased.

Fig.2 Dynamics of total emergy input-output ratio (EIR) of agricultural land in Chengdu metropolitan area during 2006-2016

Industrial emergy input-output ratio is a measure of the system’s dependence on fossil energy. The smaller the value, the greater the degree of dependence, the more the fossil energy needed to produce a unit of agricultural products[11]. From 2006 to 2016, the industrial emergy input-output ratio of agricultural land in the Chengdu metropolitan area was generally in a fluctuating downward trend (Fig.3). The industrial emergy input increased from 1.359×1023sej in 2006 to 1.411×1023sej in 2016 (Table 3). Among them, the most obvious increase was in the emergy input of nitrogen fertilizer, potassium fertilizer, compound fertilizer and agricultural film, leading to the growth of industrial subsidiary emergy. It indicates that the mechanization level of agricultural production in the area is improved continuously, and the use of fossil energy continues to grow. The Chengdu metropolitan area is located on the Chengdu Plain. The terrain is open and flat. In recent years, in order to increase the production and economic benefits of agricultural products and meet the needs of a large number of people for food, agricultural machinery has been introduced, and the use of fossil fuel quotas has been increased. This is to give full play to the geographical advantages of the area, and it is one of the effective ways to improve the level of agricultural development. The industrial emergy input-output ratio was fluctuating and decreasing, while the total emergy input-output ratio was also declining. This was caused by changes in the agricultural production structure, that is, it is the result of the relocation of livestock breeding and the increase in emergy output of planting industry.

Fig.3 Dynamics of industrial emergy input-output ratio (IEIR) of agricultural land in Chengdu metropolitan area during 2006-2016

The environmental load index is used to measure the pressure of regional economic development on the environmental system of agricultural land. The greater the value, the greater the environmental pressure[12]. Between 2006 and 2016, the environmental load index of agricultural land in the Chengdu metropolitan area fluctuated around an average value of 5.661 (Fig.4), lower than the national average of 5.89 in 2015[13]. The lowest value (5.302) appeared in 2010, and the highest value (5.916) appeared in 2011. This set of data reflects that the environmental resources in this area have not yet been fully utilized and there is room for improvement. However, since 2012, the index has been increasing, with an increase of about 6%. This is because the input of industrial subsidiary emergy and chemical fertilizers and pesticides has increased in recent years, so the environmental pressure is increasing. If no measures are taken, the environmental pressure in this area will continue to increase, which will eventually lead to serious environmental problems. Therefore, for the sustainable use of agricultural land, in agricultural production, the use of production materials such as fertilizers and pesticides should be controlled, solving the problem of environmental pollution from the source, improving the quality of agricultural products, and ensuring the security of food production.

Fig.4 Dynamics of environmental load index (ELR) of agricultural land in Chengdu metropolitan area during 2006-2016

The sustainable use index measures the sustainability and coordination of a regional eco-economic system. The greater the value, the higher the system sustainability. This index is the ratio of land emergy input-output ratio to environmental load index. It considers the economic benefits and environmental load of agricultural land, and can directly reflect the sustainable use of agricultural land. Between 2006 and 2016, the sustainable use index of agricultural land in the Chengdu metropolitan area was in a downward trend overall. The highest value was 0.223 in 2007 and the lowest value was 0.164 in 2008 (Fig.5). In terms of time period, it was in a decline phase during 2006-2008, reaching the lowest value of 0.164 in 2008; it increased from 2008 to 2010; since 2012, it tended to decline again, from 0.202 in 2012 to 0.171 in 2016, and the decrease was about 15%. This reflects the increasing trend of environmental pressure on agricultural land and the decline in sustainable use of agricultural land in the metropolitan area. The main reason is that the amount of non-renewable industrial subsidiary emergy input is increasing, and agricultural production puts increasing pressure on the environment. At the same time, it also reflects that its agricultural production is gradually shifting to a modern agricultural production model that relies on fertilizer and mechanized production to cope with increasing consumer demand. As a result, the sustainable use of agricultural land has been reduced.

Fig.5 Dynamics of sustainable use index (ESI) of agricultural land in Chengdu metropolitan area during 2006-2016

4 Conclusions and suggestions

4.1 ConclusionsSupported by Odum’s emergy theory, we learn from the experience of many related scholars. Combined with the actual situation of agricultural production in the Chengdu metropolitan area, a number of indices reflecting the sustainable performance of agricultural land were adopted. Based on the statistical yearbook of the Chengdu metropolitan area, the situation of sustainable use of agricultural land in the Chengdu metropolitan area from 2006 to 2016 was drawn. The results show that during 2006-2016, among the outputs of agricultural land in the Chengdu metropolitan area, the output of planting industry had increased significantly, and that of livestock breeding industry had decreased significantly, related to changes in the structure of agricultural production in the area. During this period, the total emergy input-output ratio of agricultural land in the metropolitan area showed a fluctuating downward trend, with a decrease of 24%. The average was lower than the national average, reflecting the low utilization rate of emergy and declining tendency of utilization efficiency in the area. From the perspective of changes in the input-output ratio of industrial emergy, it was in a fluctuating downward trend overall, indicating that its dependence on industrial subsidiary emergy and the modernization of agricultural production are continuously improving. In addition, the agricultural land environmental load index of the area fluctuated around the average value, lower than the national average, suggesting that the environmental resources in this area still have accommodation space and have not been fully utilized. However, the index has been on the rise since 2012. During the corresponding period, the sustainable use index of the area also showed a downward trend, reflecting that the sustainable use of agricultural land is declining and environmental pressure is gradually increasing.

Based on changes in emergy evaluation indices, the reasons for the decline in the sustainable use of agricultural land in the Chengdu metropolitan area are analyzed. First, the area of agricultural land has been reduced. In order to meet consumer demand, industrial emergy input is increased to improve production. Second, agricultural land has been transformed into non-agricultural land, so the area of agricultural land has reduced. In addition, the balance between occupation and compensation has been lost. Third, the level of agricultural modernization is increasing. The increase in fossil energy input such as fertilizers and agricultural machinery has caused the destruction of soil physical and chemical properties, leading to deterioration of the ecological environment of agricultural land. This is the main reason for the decline in sustainable utilization.

4.2 SuggestionsFor areas with low emergy utilization rate of agricultural land in this area, the vegetative growth of crops should be scientifically monitored, and fertilizer should be quantitatively increased, to improve the intensification of agricultural production, reduce the waste of emergy input, and improve the utilization efficiency of emergy input. In agricultural production, high-yield seeds and high-quality young animals should be used, in order to guarantee the quantity and quality of agricultural products, thereby dealing with the reduction of agricultural land area. In recent years, the environmental load index of agricultural land tends to rise and the sustainable use index tends to decline. They reflect the same problem, that is, the environmental pressure on agricultural land in the area is gradually increasing, and the ecological environment has been destroyed and the sustainable use has declined. To solve this problem, the natural resources of the Chengdu metropolitan area should be fully utilized, especially abundant water resources and purple soil resources rich in organic matter. At the same time, the use of organic fertilizers should be promoted, the input of fossil energy should be reduced, and the multiple crop index should be increased, with "improving quality and efficiency and transforming methods, stabilizing yield and increasing income and sustaining" as the main line of work, and environmental protection, production improvement and income increase as the goal of agricultural development. This is the direction of sustainable development of agricultural land in the Chengdu metropolitan area.