Assessment of the water content of the soil and utilization of the energy balance model to promote environmentally friendly development of green, low-carbon industries

Sustainable water resource management is an important research topic in the context of global climate change. The relationship between energy and water resources is becoming increasingly complex, and their degree of dependence on each other is increasing (Liu et al. 2023). Water resources are gradually becoming a complex and fragile link in the energy system. Therefore, evaluating the interaction between water resources and energy is the focus of future sustainable development research. In addition, in recent years, ‘environmental pollution’ and ‘energy crisis’ have attracted widespread attention. With the rapid development of human society, the consumption of water resources in China and even worldwide is becoming increasingly severe. The concept of sustainable development of water resources has received widespread attention from countries around the world, all of which are striving to practice green and environmentally friendly low-carbon living. Soil moisture content is a key hydrological state variable and is crucial for numerous Earth and environmental science applications that directly affect the global environment and human society (Guo et al. 2022). Determining and predicting the spatiotemporal variability of the soil moisture content is a key factor in crop production in semi-arid agricultural systems (Tunçay 2021). In order to address the increasing demand for water and energy during crop growth in agricultural production, as well as the increasingly serious water shortage problem, an energy balance model is used to analyze and evaluate the quantity and quality of water and energy in the soil.

The water content of soil and the energy balance model are physically very strongly linked. A large number of physical parameters of soil, including the water content of soil, temperature, texture, and structure need to be acquired during the application of the model. A rapid estimation of the water content of soil can be achieved through the measurement of these parameters. The water content of the soil is a key environmental variable that is important for farmers, meteorologists, and disaster management units (Bauer-Marschallinger et al. 2018). Understanding the water content of soil and its relationship to different climatic and soil characteristics is essential for better analyzing the interaction between forest and soil water dynamics (Qiu et al. 2023), and thus allowing us to predict climate change more accurately (Dincă et al 2018). With growing emphasis on environmental protection and development of green industries, higher requirements have been put forward for agricultural development. In order to meet the increasing needs of a good life, construction of ecological civilization, and sustainable development of agriculture, the use of the energy balance model for the study of the water content of the soil is of great importance in promoting green and low-carbon environmental protection in industries (Shang & Luo 2021).

Research on the water content of the soil is of great significance to the development of agriculture and can contribute to the promotion of green industry; therefore, research on the water content of soil has always attracted a wide range of scholars. Stocker et al. (2018) suggested that limitations of the water content of soil strongly affected plant physiology. Al-Khaldi et al. (2019) presented a time series inversion of soil water obtained from a cyclonic global navigation satellite system constellation. Humphrey et al. (2021) found that the feedback mechanism of soil, water, and atmosphere amplified temperature and humidity anomalies, and enhanced the direct impacts of soil water stress. Mohamad et al. (2020) found that people were interested in rapid drying time capability, especially for application in organic soils such as peat. This is because peat soils have high water and organic contents. Zhou (2021) demonstrated that soil water strongly influenced future surface water changes, especially in dry land, by regulating evaporative transpiration and atmospheric water influx. Zhang et al. (2019) examined the effects of soil water changes in the root region on regional carbon fluxes in seven North American ecosystems. Samaniego et al. (2018) anticipated that anthropogenic warming would exacerbate soil water drought in the future. However, predictions were accompanied by substantial uncertainty due to different estimates of future warming. Frindte et al. (2019) showed that microbial community composition was dependent on near-ground temperature and soil water status for long-term development with some resilience. With the increasing emphasis on the green and low-carbon environmental development of industries, the determination of the water content of soil has also become a high priority, and previous studies have not done an in-depth study on the role of energy balance models in them, and there are still some limitations in the actual operation process.

There are many ways in which the water content of the soil has been determined, and there are many scholars who have studied it. Kim & Lakshmi (2018) studied the limitations and capabilities of cyclonic global navigational satellite system observations for soil water estimates (0–5 cm). Liang et al. (2019) suggested that global navigational satellite system interferometric reflectometry was a new remote-sensing technique that could be used to estimate near-surface soil water based on signal-to-noise data. Klotzsche et al. (2018) found that since the establishment of radar on Earth as a tool for the determination of the water content of soil in seep belt hydrography about 25 years ago, tremendous progress has been made on radar equipment in Earth discovery, data acquisition, and processing. With the increasing scarcity of water resources, the water content of soil in agriculture is of extraordinary importance to the growth of agricultural crops and is important to the practice of green industry. This study is based on the energy balance model for the determination of the water content of soil.

This paper presents an evaluation of the water content of soil based on an energy balance model and a design of measurement experiments which showed a large degree of variation in the hygroscopic water content measured by the oven-drying method for loamy soil after air drying. The measured hygroscopic water content results for a loam sample were between 10% and 20%. The magnitude of variation for the hygroscopic water content measured by the energy balance model for a loamy soil after air drying showed a relatively gentle change, which remained between 10% and 15%. It can be seen that the energy balance model is more precise and more stable for the determination of the water content of soil.

The water content of soil is an important factor affecting soil quality. Water is one of the most important components of soil, and the content and form of soil water have an important impact on the process of soil formation and development, fertility level, and self-purification ability (Ran et al. 2023). Changes in the water content of soil directly affect crop growth and development. When soil water is insufficient, plant growth slows down, which is not conducive to crop absorption of nutrients and affects crop yield. The movement of soil water makes organic and inorganic matter constantly migrate and transform in the soil profile so that nutrient elements in the soil migrate to the plant root zone and are absorbed and utilized by plants (Li et al. 2023). When there is too much water, it may make the respiration of crop roots vigorous, lengthen the root system, reduce or even shed root hair and reduce the absorption capacity, so that crop growth and development may be affected. The state of soil water can be solid, liquid, and gas. The type of soil water can be roughly divided into chemically bound water, hygroscopic water, and free water. Among these, hygroscopic water and free water are commonly used for determination.

In addition, the water content of soil also directly affects microbial activities in the soil and, in turn, affects soil physicochemical properties (Yang et al. 2022). At the same time, water affects the decomposition and transformation of soil materials. As a solvent, water is not only a transport carrier of trace elements in soil, but also a necessary condition for the survival of some microorganisms. The water content of soil shows a clear diurnal and seasonal variation pattern in the range of 0–15 cm. The water content of soil is higher during the day and lower during the night. In general, shallow soil has much higher water content than the deep soil that lies below 10 cm.

At present, green and low-carbon industry includes green manufacturing, green energy industry, green environmental protection industry, and so on (Yang et al. 2023). Although these industries belong to the high-tech field, at present, they still have many problems in development. From industry as a whole, these industries are still emerging, have not formed economies of scale and are not yet competitive internationally. The following main questions remain:

• (1)

  There is insufficient investment in research and development of the technology, and the research and development capacity is weak. At present, society has insufficient scientific research inputs in green and low-carbon industry, which makes it difficult to form an adequate technical reserve and innovation capacity. Green manufacturing is a traditionally dominant industry and one of the pillar industries in the national economy, but currently accounts for a smaller proportion of manufacturing worldwide. At the same time, green energy industry, green environmental protection industry, and others are also emerging industries, which have high technology content and long research and development cycles and need a long-term massive capital investment and a large pool of scientific and technological talents. From the current state of economic development, these two major industries do not yet have the conditions to support economic high-quality development.

• (2)

  There is a funding shortage. Green and low-carbon industry needs a large amount of financial support in development, especially for green manufacturing industry and green environmental protection industry, to achieve industrial and scaled-up development. In terms of the current state of the situation facing the development of green low-carbon industry, the funding-shortage phenomenon is quite prominent. On the one hand, the government has insufficient financial input. On the other hand, problems such as poor financing channels, high financing costs, and high risks in capital markets are prominent.

• (3)

  There is talent deficiency. The development of green low-carbon industry needs a large amount of high-quality talent to invest in related fields, but the current talent pool in this area is significantly insufficient. According to statistics, the current high-end talent gap in the green low-carbon sector is at least 2 million people. Compared with other countries, China has a more severe shortage of high-end talent in this field.

• (4)

  There is an imperfect industrial chain. The current green low-carbon industry has some problems such as an imperfect industry chain and an incomplete supply chain. There is also a lack of leading firms and industry giant firms in related fields in the green low-carbon industry, resulting in a difficulty for these firms in forming size effects and synergies during their development.

The water content of soil is one of the important factors affecting the development of green low-carbon industry. As a soil component, water is the carrier of soil material migration and movement and an important material basis for soil energy transformation. It has an important impact on many aspects, such as land use, agricultural production, and environmental protection. From a land use perspective, an increase in the water content of soil can expand the agricultural planted land area, improve the yield and quality of agricultural crops and promote the healthy development of green low-carbon agriculture. From the viewpoint of agricultural production, changes in water content of soil can directly affect the growth, development and yield of agricultural crops, which in turn are indispensable in agricultural production. Therefore, the water content of soil is bound to have an important impact on the development of green low-carbon industries. Meanwhile, the water content of soil also has a profound effect on environmental protection. Under the premise of maintaining an ecological balance, an appropriate increase in the water content of soil can improve the water retention capacity of the land, slow the rate of water evaporation from the land, and reduce water loss, thus preventing environmental problems such as drought and desertification. These environmental problems affect not only agricultural production but also other industries and residents' lives, so the rational regulation and improvement of the water content of soil is one of the necessary conditions for the development of green low-carbon industries.

Water content of soil is one of the key factors affecting the development of green low-carbon industries. Exploring the impacts of water content of soil on agricultural production and environmental protection can help to better understand the laws of land use, grasp the rhythm of land resource use, and further promote the sustainable development of green low-carbon industries. Therefore, people should strengthen soil management, improve water content of soil, and accelerate the pace of green low-carbon industry development, contributing to the realization of green low-carbon environmental and sustainable development of industries.

Energy balance is to analyze the balance between the input energy, effective utilization energy, and loss energy of a system. The energy balance model is based on the law of energy conservation and the relationship of energy transformation, using the equilibrium equation to calculate the change law of soil water, nutrients and temperature, and in turn, to realize the prediction of water, temperature, and so on in the soil.

If water content of soil is to be calculated using the energy balance model as shown in Figure 1, it can be calculated using an equilibrium equation based on the energy produced by the mass of soil water and temperature change in the outside world, ultimately yielding the water content of soil and the magnitude of the energy released to the outside world. Usually, the energy balance model can be used in corporate production. When the mass of input changes, the calculated resulting energy also changes, producing a change in energy called energy utilization. Through energy balance, improving the level of energy utilization and analyzing the factors affecting each link in the process of energy consumption, the reasons for energy loss, and the potential ways of energy saving are found to formulate practical technical transformation measures to improve the energy utilization rate of the system.

Since the energy balance model is not only suitable for the water content of soil detection but can also be applied to other fields, the formulas for calculating the energy utilization also change accordingly when the energy objects that need to be calculated are changed. In general, there are three methods.

The energy balance model in this article does not need to calculate too complex an energy utilization efficiency, but only needs to use an equilibrium formula to determine the water content of soil.

Changes in water and energy in soils directly affect agricultural production, ecosystem management, environmental protection, and so on. The development of agricultural production has a limited need for soil water, whereas ecosystem management requires soils to have some capacity for self-regulation. The use of the energy balance model for simulation makes it possible to calculate the situation of the water content of soil, and thus to understand the relationship between agricultural production and the ecological environment, which provides a scientific basis for developing corresponding management policies.

The water content of soil is an important environmental parameter and an important indicator for evaluating the physical properties of the soil. The energy balance equation in the energy balance model is also an important module for modeling changes in soil water and soil quality. Because soil water and energy balance models share the same basic characteristics in describing the physical properties of the soil, there is a close connection between them. On the one hand, the water content of soil is one of the input parameters in the energy balance model. On the other hand, the energy balance equation in the energy balance model can be described by soil water status. Mathematically, there is a correspondence between the energy balance equation and the water content of soil. Therefore, these linkages must be considered when studying and evaluating the changing role of the water content of soil on the development of low carbon in green industry.

The complex relationship between water and energy can be analyzed through systematic methods, comprehensively considering the mutual influence of water and energy in various aspects, and exploring their complementarity and potential synergy across departments. When planning energy and water resources, it is necessary to better integrate these two aspects to maximize the optimization of industrial water and energy inputs, while avoiding inefficient issues. Energy utilization should fully consider the limitations of water resources, maximize the synergistic effects of the system, and minimize the negative effects of the system. When assessing the needs of the energy industry, water resource planning and policymakers must take into account the demand for water resources from industrial production, power generation, and mining, as well as their impact on water sources. Similarly, the complexity of the water cycle and other competitive demands should also serve as a reference for energy engineering planning and investment estimation. The integrated planning of energy and water resources is an effective way to achieve sustainable utilization of the two major resources, enhance their synergistic effects, promote multi-disciplinary cooperation, and achieve coordinated development of water and energy at the national and regional scales.

Energy and water resources are mutually interconnected, so the implementation of an energy-saving or water-saving measure or technology will have a synergistic effect. The synergistic effect depends on the energy utilization intensity of water resources. However, considering the mutual feedback relationship between the two, the synergistic effect of water-saving and energy-saving technologies is greater in areas with high water and energy utilization intensity. When both values are large, the synergistic effect is also significant. From different scenarios, the maximum energy savings under water-saving scenarios indicate that the development and utilization of unconventional water and the use of water-saving energy technologies can effectively alleviate the pressure on water resources in energy bases. We need to increase investment in research and development of water-saving technologies, promote new water-saving technologies, improve the comprehensive utilization level of mine water, and promote the application of distributed underground reservoir technology in coal mines and high salinity coal mine water desalination technology. Compared with the demand for water resources in energy production, the proportion of energy used in water supply is relatively small.

Soil water is an important component and fertility factor of soils. Soil water's status type and dynamics are greatly different in different climatic and biological conditions (Zhang et al. 2021). Studying the types and dynamics of soil water status has very important theoretical and practical significance for mastering the formation, classification, distribution, fertility, and field soil water regulation of soil. The hygroscopic water content and natural water content of soil were obtained through experiments to understand the changing situation of soil water, ultimately to make the best use of soil resources and build a green and low-carbon environmental protection industry.

Soil samples were collected before the experiment. To ensure that the experiment was not disturbed by other irrelevant conditions, the selected soil was maintained under controlled conditions. A field survey of the soil was required before soil selection. Finally, the three most representative soil types were selected for the experiment, which were sandy soil, clayey soil, and loamy soil, respectively.

The collection process of the sampled soils is complex and requires sampling using a cutting ring, small iron hammer, and soil spatula. First, a layer of petrolatum was applied on the cutting ring wall to increase lubrication, and then the cutting ring edge was vertically pressed into the soil, using a small iron hammer assisted by a slow tapping of the spatula to prevent the cutting ring from binding too deep into the soil and thus destroying the soil structure, until the soil was covered with the full cutting ring barrel. Then, an iron spatula was used to excavate the cutting ring. After the soil adhering to the outside of the ring knife was wiped clean, a protective cuff was added to both sides of the ring knife in time to prevent soil water evaporation from affecting the experimental results. Pending the acquisition of all types of soil samples, 15 samples of each of the three types were divided as required, individually labeled on demand, and placed in plastic bags for further use. Table 1 shows the situation of the collected soils.

Air-dried soils occur because freshly collected soils are inherently equipped with a range of soil water, which is constantly evaporated in the air. Air-dried soil refers to fresh soil that is left indoors and the water in the soil is lost by continuous evaporation. When the water in the soil reaches equilibrium with the water in the air (it usually takes several days), the soil is called ‘air-dried soil’. In this paper, 15 soil samples were subjected to the air-dried soil experiment and the oven-dried soil experiment. Because air-dried soil still contains some moisture that is tightly absorbed by soil particles and cannot enter the air, this moisture is called hygroscopic water (Bai et al. 2021). Hygroscopic water can be dried through human experiments, and the soil at this time is called ‘dried soil’. The natural water content of soil and its changes can be calculated by the weight difference between air-dried soil and oven-dried soil.

For the dry-out method, the 15 sampled soils from the three types of soil collected were first placed individually in suitable containers, and were labelled according to the type of soil. The total weight of the soil and container at the beginning was recorded using an electronic weight, and then the container containing the soil samples was placed in a ventilated laboratory for ten days. After ten days, the soil samples were weighed again and the total weight of the soil and container was recorded. The natural water content of the soil was calculated by calculating the difference between the two.

For the energy balance model, the model was calculated by the equilibrium equation directly by simulating the conversion process between soil water and air substance energy. The use of the energy balance model to calculate the water content of the sample soil of the three types did not need to go through the above steps; the model was simply used to carry out the analysis of the simulation results of the sample soil.

In Figure 3, it can be seen that the sandy soil did not have a high natural water content. Neither the oven-drying method nor the energy balance model gave results for natural water content determination of sandy soils that exceed 40%. From Figure 3(a), it is shown that the same batch of sample soil had natural water contents between 30% and 40%. The second sandy soil sample had the highest value of 39.2% and the 15th had the lowest value of 30.3%, which was a large gap of 8.9%.

Figure 3(b) presents the results of the natural water content determination of sandy soil using the energy balance model. It can be seen that the results of the natural water content of the sandy soil determined using the energy balance model were more stable with the 15 sandy soil samples remaining between 30% and 35%. The lowest natural water content determination was 30.12% for the fifth sample and the highest was 34.46% for the third sample, which differed only by 4.34%. The gap was not too large.

Figure 4 shows the results of the natural water content determination of 15 clay samples in two ways. On comparing the results of the natural water content determination, it was found higher for clayey soil than sandy soil. First, in Figure 4(a), it shows that this batch of clay samples had a natural water content between 80% and 90% as determined by the oven-drying method. The lowest natural water content value was 80.21% as determined for the tenth clay sample and the highest was the measurement of the 11th clay sample with 89.71%, which was calculated to differ by 9.5%. In Figure 4(b), similar to the oven-dried method, the natural water contents of this batch of clay samples determined by the energy balance model were also above 80%, but the results of their determination were controlled between 80% and 85%. The difference between the highest and the lowest value determined was 4.28%. The highest result was found to be 84.86% for the first batch of clay samples. The lowest result of the natural water content determination was 80.58% for the 11th clay sample.

Figure 5(a) presents the results of the measurement of the natural water content of the loamy soils examined by the oven-dried method. It was found to be between 50% and 60% with the highest extent of 59.84% for the sample soil of the 15th loamy soil sample and the lowest of 50.01% for the ninth loamy soil sample, which differed by 9.83%. Figure 5(b) shows the results of the determination of the natural water content of the loam by the energy balance model. The natural water content of the loamy soil determined by the energy balance model was held between 50% and 55%. The highest value was 54.58% for the seventh loamy sample and the lowest value was 50.01% for the fifth loamy sample, which was the same as the lowest value for the sample soil of the loam as determined by the drying method.

After the data analysis of Figures 3–5, it can be seen that the energy balance model was more stable in the determination of the water content of soil. The difference in results between water contents of the same batches was controlled within 5%, while the oven-drying method is not only cumbersome for determining the process, but also not highly accurate for observing and recording in the field at all times. It is easier to calculate the energy balance model by way of energy conversion, having higher accuracy.

The purpose of performing the oven-dried soil experiment was to explore the content of hygroscopic water in the soil. Therefore, when determined using the oven-drying method, it was necessary to experimentally dry the soil that had been naturally air-dried. An oven was used for water evaporation treatment to control the temperature between 110 and 120 °C. Promptly placing the sample soil into a dry container after the end of the oven-drying for cooling was done before recording the weight of the soil. The difference is the amount of hygroscopic water, compared with the weight of air-dried soil before drying.

The energy balance model was directly used to decompose the components of the air-dried soil. The water and energy contained in the air-dried soil were extracted and calculated. The contained hygroscopic water content was analyzed. Unlike the oven-drying method, the energy balance model mainly utilized computer technology and an equilibrium formula to computationally evaluate the hygroscopic water content of air-dried soils. Figure 5 is a case of the hygroscopic water content of air-dried soil determined by the two methods separately.

A comprehensive observation can reveal that the hygroscopic water profiles of different soils were also not the same. Furthermore, the results determined by the oven-drying method showed a larger variation, whereas the results for the hygroscopic water content of soil samples determined by the energy balance model showed a smaller variation. Variation in water content results appeared when soils were from the same batch. The distribution of water among soils was differential, but not so much for the same conditions. The results determined by the oven-drying method were significantly more erroneous than those determined by the energy balance model. The experiment proved that the energy balance model was better. Different soil water content has different impacts on different types of ecosystems, so studying water content of soil is of practical significance for ecosystems.

In the present era of practicing the low-carbon ecology of green industries, green ecology is a topic of common concern, and determination of changes in the water content of the soil can help agricultural production. Water content data can provide a basis for crop cultivation and irrigation. Research on changes in the water content of soil can also play a certain warning role in changes in hydrography and watershed water content. Therefore, the convenience and precision of a certain method for the determination of the water content of soil needs to be studied. In this paper, the energy balance model was used to determine the water content of soils and compared with the conventional oven-drying method to explore the advantages of the energy balance model, which also proved that the energy balance model could effectively determine the hygroscopic water content and the natural water content of soils. However, this paper also has some problems while achieving certain results. First, due to the limitation of the experimental field, experiments on the drying method could only guarantee to be conducted in a ventilated laboratory, and were not sterile and undisturbed by the experimental environment. The experimental results had certain errors. Second, only 15 soil samples from three soil types were selected for the experiment in this study, which had a small capacity and lacked data support. Also, the experimental results were not representative due to the short time limit and the samples selected could not be completely consistent due to the experimental site. Finally, because the study of the water content of soil is essential for the development of the ecology, agriculture, and green industries, the experiments in this paper could only provide a theoretical basis for the energy balance model, which still faces many unknown challenges to be truly implemented. It is believed that the solutions to these problems are a matter of time. In order to gain a deeper understanding of the effects of using water content of soil and the energy balance model to promote the green, low-carbon, and environmentally friendly development of industries, the analysis results will be further refined in light of these issues in subsequent studies.

Data cannot be made publicly available; readers should contact the corresponding author for details.

The authors declare there is no conflict.