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Article

Effect of Soil Moisture Content on Condensation Water in Typical Loess and Sandy Soil

by
Cheng Jin
1,2,3,
Zhifeng Jia
1,2,3,*,
Ge Li
1,2,3,
Lingke Zhao
4 and
Yuze Ren
5
1
School of Water and Environment, Chang’an University, Xi’an 710054, China
2
Key Laboratory of Subsurface Hydrology and Ecological Effects in Arid Region, Ministry of Education, Chang’an University, Xi’an 710054, China
3
Key Laboratory of Eco-Hydrology and Water Security in Arid and Semi-Arid Regions of the Ministry of Water Resources, Chang’an University, Xi’an 710054, China
4
Xianyang Water Conservancy Team, Xianyang 712000, China
5
China Certification & Inspection Northwest Ecological Technology (Shaanxi) Co., Ltd., Xi’an 710018, China
*
Author to whom correspondence should be addressed.
Land 2024, 13(7), 934; https://doi.org/10.3390/land13070934
Submission received: 10 May 2024 / Revised: 5 June 2024 / Accepted: 22 June 2024 / Published: 27 June 2024
(This article belongs to the Section Land, Soil and Water)
Browse Figures
Versions Notes

Abstract

:
Many scholars have used samples of drying soil to observe the amount of soil condensation water, which may have exaggerated the amount of regional condensation water, as the soil water content in the natural state was not considered. To analyze the effect of soil moisture content on soil condensation in the natural state, the soil condensation volume in loess and sandy soil under different gravimetric moisture content conditions was measured in the autumn of 2022 and spring of 2023 using micro-lysimeters combined with the weighing method at the groundwater and environment site of Chang’an University, Guanzhong Basin, China. The results showed that the average daily condensation of loess under 0%, 3%, 7%, 11%, and 15% moisture content conditions was 0.34, 0.09, 0.01, −0.05, and −0.07 mm with the condensation days of 54, 40, 24, 21, and 16, respectively, and that of sandy soil was 0.21, −0.02, −0.28, −0.82, and −1.35 mm with condensation days of 54, 24, 2, 3, and 1, respectively. Under the same moisture content conditions, loess had more condensation and condensation days than sandy soil. Soil condensation water occurred mainly when the water content was less than 7%, and it was negatively correlated with soil water content. The quantity of soil condensation water was positively correlated with relative humidity and negatively correlated with air temperature–dew point differences. Relative humidity exceeding 60% and air temperature–dew point differences below 8 °C were more favorable for the formation of soil condensation water. This study provides a reference for the assessment of soil condensation in the natural state.

1. Introduction

In arid and semi-arid regions, water shortage has become a key problem restricting the regions’ ecological construction and economic development due to scarce rainfall and strong evaporation. It has been shown that condensation water can be directly absorbed and utilized by shallow-rooted plants or soil organisms and is a more efficient source of water than precipitation [1,2]. It is important for plant growth and the survival of soil organisms and plays a unique ecological role in sustaining fragile ecosystems in arid and semi-arid regions [3,4,5,6]. Soil condensation water is liquid water from atmospheric water vapor and water vapor in soil pores that condenses in the surface soil when the surface soil temperature reaches the dew point and becomes a component of soil water [7,8,9]. The process of water vapor condensation often occurs in conjunction with vapor adsorption in soil. Soil adsorption water refers to the water that adheres to the surface of soil particles in the form of film water and adsorbed water layers on the surface of dry soil particles [10,11,12]. Soil adsorption water and condensation water are known as adsorption–condensation water [13,14]. The soil condensation water investigated in this study also falls under the category of adsorption–condensation water.
Soil condensate should not be neglected in the hydrological cycle of dry regions. For example, non-precipitating land surface water dominated by condensate can account for 9% and 33% of the total source of land surface water in the Gurbantunggut Desert and Taklamakan Desert regions in Xinjiang, China, respectively [15,16]. The amount of condensate accounted for 20.18% of rainfall from autumn to spring in the Kubuch Desert of the Inner Mongolia Autonomous Region in China [17]. The amount of condensed water in the annual water balance reaches 8.68% in the Arid Valley region of the western United States [18]. Moro et al. found that the contribution of condensed water to the water balance reaches 12% [19]. In addition, condensation may be detrimental to plant growth and development—for example, dew forms a water film on the plant surface that favors the germination of pathogen spores [20]. Soil condensation water is mainly influenced by atmospheric relative humidity, air temperature–dew point difference, wind speed, and cloud cover [20,21]. Higher atmospheric relative humidity provides abundant water vapor for soil condensation, encouraging continuous condensation [22]. Smaller air temperature–dew point differences provide the impetus for soil condensation, which benefits soil condensation [23]. Wind influences the diffusion and exchange of water vapor in the air, and a moderate wind speed ensures that there is enough water vapor in the air to cause condensation [24,25]. When it is clear and cloudless at night, the ground temperature drops more rapidly, which favors vapor condensation [23,26].
In the mid-latitude arid and semi-arid zones of the Northern Hemisphere, such as the Loess Plateau in China [27] and parts of Europe [28] and North America [29], there are large amounts of loess, covering an area of up to 94,000,000 km2 [30], while in the arid and semi-arid regions of the globe, such as the Sahara Desert [31], the Arabian Desert [32], the Australian Desert [33], and the northwestern part of China [34], there are large amounts of sandy soils, covering an area of up to 9,772,000 km2. Due to the differences in the physical properties of soil, such as particle size, bulk density, and structure, there are differences in the condensate produced by different soil types. In this study, two typical soils, sandy soil and loess, were selected to carry out a comparative analysis of condensation water [35,36,37,38]. In previous studies, dry soil samples were often selected and placed in the field to observe condensation [39,40,41]. However, the surface soil in the natural environment is not always dry, especially before and after rainfall, when soil moisture content is high and largely evaporated. If dried soil samples are placed in the field before and after rainfall, there will inevitably be significant soil condensation, and the observed values will not accurately reflect the amount of soil condensation in the region. The soil water content in this natural state was not considered [42,43,44,45], thus neglecting its effect on condensation, which may lead to bias in the estimation of soil condensation. Therefore, we simulated soil that was not completely dry by formulating soil samples with varying levels of water content.
There are some methods for observing condensate, such as the micro-lysimeter meter combined with the weighing method, the Duvdevani condensate meter method [46], the Hiltner dew balance meter method [47], the soil moisture sensor method [48], and so on. The micro-lysimeter meter combined with the weighing method to determine soil condensate works on the principle of water balance. Most scholars have adopted this method because of its simple structure, easy operation, no limitation of time and space, and no damage to the original structure of the soil, and because it is especially suitable for the observation of condensate in the field [49,50,51,52,53,54,55,56]. In this study, hand-made micro-lysimeters were used to observe the amount of soil condensate under different soil moisture content conditions using the weighing method to analyze the relationship between soil moisture content and soil condensate [39,40,41]. This study not only fills the gap in the existing literature on the behavior of soil condensate under incompletely dry soil conditions but also provides a new perspective for understanding soil condensate water in arid and semi-arid regions.

2. Materials and Methods

2.1. Measurement Site

The experimental station was located in the middle of the Guanzhong Plain, China, as shown in Figure 1. The Guanzhong Plain is also known as the Weihe Alluvial Plain in central Shaanxi Province, extending from Baoji in the west to Tongguan in the east, and from the Qinling Mountains in the south to the Huanglong Mountains and Ziwuling Mountains in the north. The field experiment was conducted at the groundwater and ecological environmental in situ experiment site (34°22′8.34″ N, 108°54′28.44″ E), Weishui Campus, Chang’an University, Xi’an City, Shaanxi Province. The site is situated within the transitional zone of the warm temperate zone, exhibiting characteristics of both a semi-humid monsoon climate and a continental monsoon climate. It experiences a distinct seasonal shift, with cold winters and hot summers. The annual average temperature is 13.0–13.7 °C, with an average temperature of −1.2–0 °C in the coldest month (January) and 26.3–26.6 °C in the hottest month (July). Annual precipitation ranges from 522.4 to 719.5 mm, and annual potential evapotranspiration ranges from 1200 to 1400 mm. The zonal vegetation belongs to the warm-temperate deciduous broad-leaved forest zone and is rich in tree and shrub species. The plant community structure is dominated by a “tree-shrub-herb” type of vegetation, with Rosaceae, Oleaceae, Caprifoliaceae, and Leguminosae as the main dominant species [57,58].

2.2. Experimental Materials

The micro-lysimeter consisted of inner and outer tubes with diameters of 7.5 cm and 9 cm, respectively. The height of the micro-lysimeter was 10 cm (Figure 2a). The inner tube was filled with soil of varying soil gravimetric moisture content. The upper part of the inner tube was unsealed, and the bottom was sealed with a 300-mesh nylon mesh so that water vapor in the air near the surface and soil pores could be exchanged within the micro-lysimeter, and the soil particles would remain in the cylinder. Gravel, which was approximately 1 cm thick, was placed at the bottom of the outer pipe to reduce soil capillary action.
Two soil types, loess and sandy soil, were selected for this experiment: the loess sampling site was located in Ansai District, Yan’an City, Shaanxi Province, and the sandy soil sampling site was located on the south bank of the Wei River in Xi’an City, Shaanxi Province. The loess structure is massive loose and porous, and the sandy soil structure is granular and disorganized. A ring knife with a volume of 200 cm2 was utilized to collect the in situ soil from the soil profile, which was dried for more than 8 h after collection, and the soil bulk weights at different depths were obtained by calculating the weight of the soil per unit volume after drying. According to the calculations, the soil capacity of loess soil was 1.40 g/cm3 and that of sandy soil was 1.60 g/cm3. The dried soil samples in the ring knife were ground and sieved (2 mm aperture sieve), and then a Bettersize 2000 laser particle size analyzer was used to determine the particle gradation of the soil at the sampling site, as shown in Table 1. Based on the analysis of the physical properties of soil in arid and semi-arid regions, the gravimetric moisture content of loess during non-rainfall periods is generally below 20%, while sandy soil has a moisture content lower than 15%. Therefore, five treatment groups with soil gravimetric moisture content of 0%, 3%, 7%, 11%, and 15% were established for each soil type. To ensure accuracy, each treatment was repeated on three separate occasions.

2.3. Experimental Design

Because condensation in the Guanzhong Plain region mainly occurs in fall, followed by spring [59], two periods, 12 October 2022–17 November 2022 (fall) and 22 February 2023–19 April 2023 (spring), were selected for the observation of soil condensation water. Before sunset and the next day before sunrise, the micro-lysimeters were weighed using an electronic balance with an accuracy of 0.01 g. The change in its mass was considered as the quantity of condensate on that day [60].
Rainfall was measured using an ECRN-100 rain gauge (Decagon, WA USA; accuracy: ±0.2 mm) placed 100 cm above the ground. Atmospheric relative humidity (RH) and temperature were observed using a VP-3 sensor (Decagon, WA 99136 USA; accuracy: RH ± 2%, air temperature ± 0.1 °C) placed 5 cm above the ground. A GS-3 sensor (Decagon, WA 99136 USA; accuracy: VWC: ±3%, temperature: ±1 °C) was buried about 1 cm below the ground to collect soil moisture and soil temperature. All sensors were set to automatically record at an interval of 30 min using an EM50 data collector. The field layout is shown in Figure 2b.

2.4. Data Processing

2.4.1. Soil Condensation Water

The quantity of soil condensation water was expressed as the mass change observed in the micro-lysimeter every morning and evening [61,62,63], which was converted to height per unit area using Equation (1):
W = ∆ m ρ π r 2 × 10
where W is the quantity of soil condensation water (mm)—when W is greater than 0, condensation occurs; when W is less than 0, evaporation occurs; when W equals 0, there is a dynamic equilibrium between condensation and evaporation; Δm is the difference between the sunset and sunrise measurement mass of the micro-lysimeter (g); ρ is the density of water (g/cm3); and r is the inner diameter of the micro-lysimeter cylinder (cm).

2.4.2. Dew Point Temperature

The dew point temperature was calculated using Lawrence’s equation as follows: [60,64]
t d = B 1 ln R H 100 + A 1 t B 1 t A 1 − ln R H 100 − A 1 t B 1 t
where t and td are air temperature and dew point temperature (°C), respectively, RH is the atmospheric relative humidity (%), and A1 and B1 are Alduchov and Eskridge’s recommended coefficients: A1 = 17.625 and B1 = 243.04 °C [65].

2.4.3. Data Statistics and Analysis

After analyzing the processed data, histograms of both variables were found to follow an approximately normal distribution [66]. Consequently, the Pearson product-moment correlation coefficient method was employed to test the correlation between soil moisture content and soil moisture absorption and condensation [67,68].
To minimize errors caused by manual measurement, the average values of the daily weight changes in the three micro-lysimeters within each group were taken as the observation. Data analysis and graph creation were performed using Excel 2019 and Origin 2021 software, and the correlation analysis was conducted using the Pearson product-moment correlation coefficient method in SPSS 26 software.

3. Results and Discussions

3.1. Analysis of Meteorological Factors

The variations in atmospheric relative humidity (RH) and rainfall during the two periods (12 October–17 November 2022 and 22 February–19 April 2023) are shown in Figure 3. There were 22 rainfall days during the monitoring period, including 19 days of light rainfall (0–10 mm/d), two days of medium rainfall (10–25 mm/d), and one day of heavy rainfall (25–50 mm/d). The total rainfall was 120.2 mm. The average daily RH during the two periods was 74.23% (RH1) and 64.58% (RH2). The maximum RH over the entire monitoring period was 86.03% (2 April 2023), and the minimum RH over the entire monitoring period was 35.47% (14 March 2023). Overall, the average RH in the first period (fall: RH1) was greater than that in the second period (spring: RH2).
Daily air temperature, soil temperature at 1 cm below the ground, and dew point temperature showed similar trends, as shown in Figure 4. During autumn, the daily average air temperature showed an overall decreasing trend, with a mean temperature of 14.1 °C, maximum temperature of 18.1 °C (16 October), and minimum temperature of 8.9 °C (17 November). The dew point temperature remained lower than the air temperature, with a mean value of 9.6 °C, the highest temperature being 12.6 °C (15 November) and the lowest being 4.4 °C (17 November). The mean soil temperature was 15.8 °C, with the highest being 18.5 °C (16 October) and lowest being 11.4 °C (17 November). In contrast, the daily average air temperature during spring showed an overall increasing trend, with a mean value of 13.1 °C, peak value of 24.1 °C (19 April), and valley value of 5.4 °C (1 March). The mean dew point temperature was 6.4 °C, with a high temperature of 15.7 °C (18 April) and low temperature of −2.7 °C (12 March). The mean soil temperature was 13.6 °C, the peak value was 21.7 °C (19 April), and the lowest value was 6.9 °C (22 February).

3.2. Variations in Soil Condensation Water

The daily condensation quantities in loess and sandy soil under different soil moisture content conditions during the monitoring period are shown in Figure 5. As for loess (Figure 5a), the mean daily condensation quantity under 0% moisture content conditions was 0.34 mm, with a maximum of 0.74 mm (6 April 2023) and a minimum of 0.02 mm (18 April 2023). Under 3% and 7% moisture content conditions, the mean daily condensation quantities were 0.09 mm and 0.01 mm, respectively, with a maximum of 0.61 mm and 0.82 mm (12 October 2022) and a minimum of −0.21 mm and −0.41 mm (18 April 2023), respectively. Under 11% and 15% moisture content conditions, the mean daily condensation quantities were −0.05 mm and −0.07 mm, respectively, with a maximum of 0.35 mm (13 April 2023) and 0.34 mm (13 October 2022) and a minimum of −0.49 mm and −0.57 mm (19 April 2023), respectively.
As for sandy soil (Figure 5b), the mean daily condensation quantity under 0% moisture content conditions was 0.21 mm, with a maximum of 0.72 mm (13 April 2023) and a minimum of 0.04 mm (13 November 2022). Under 3% moisture content conditions, the mean daily condensation quantity was −0.02 mm, with a maximum of 0.24 mm (19 October 2022) and a minimum of −0.39 mm (25 March 2023). Under 7% and 11% moisture content conditions, the mean daily condensation quantities were −0.28 mm and −0.82 mm, respectively, with a maximum of 0.24 mm and 0.18 mm (29 October 2022) and a minimum of −1.61 mm and −4.00 mm (4 November 2022). Under 15% moisture content conditions, the mean daily condensation quantity was −1.35 mm, with a maximum of 0.35 mm (29 October 2022) and a minimum of −4.97 mm (21 October 2022).
The cumulative condensation quantities and condensation days in loess and sandy soil under different soil moisture content conditions during the monitoring period are shown in Figure 6. The cumulative condensation quantities in loess and sandy soil vary significantly under different soil moisture content conditions. Throughout the entire observation period, the total condensation quantities in loess decreased under 0%, 3%, 7%, 11%, and 15% moisture content conditions, with the quantities being 18.26 mm, 4.90 mm, 0.46 mm, −2.71 mm, and −3.67 mm, respectively. The corresponding numbers of condensation days for these moisture content conditions were 54, 40, 24, 21, and 16, respectively. For sandy soil, the total quantity of condensation water decreased under 0%, 3%, 7%, 11%, and 15% moisture content conditions, with the quantities being 11.59 mm, −1.27 mm, −14.86 mm, −44.19 mm, and −72.75 mm, respectively. The corresponding numbers of condensation days for these moisture content conditions were 54, 24, 2, 3, and 1, respectively.
Comparing the cumulative condensation quantity and condensation days in loess and sandy soil shown in Figure 6, it is found that under the same water content conditions, not only the condensation quantity of loess is larger than that of sandy soil but the condensation days of loess are also many more than those of sandy soil. As shown in Figure 6a, the condensation quantity of loess and sandy soil is negative when the soil water content is greater than 7%. It means that evaporation plays a leading role in soil water content greater than 7%. As shown in Figure 6b, when soil moisture content increased from 0% to 3%, the number of condensation days for loess decreased from 54 to 40, a change rate of 26%, and for sandy soil, it decreased from 54 to 24 days, a change rate of 56%. When soil moisture content increased from 3% to 7%, the number of condensation days for loess decreased from 40 to 24, a change rate of 40%, and for sandy soil, it decreased from 24 to 2 days, a change rate of 92%. When soil moisture content is greater than 7%, the number of condensation days for loess show a slow decreasing trend, while those for sandy soil are very small and show no obvious change. On the whole, when soil moisture content is greater than 7%, evaporation occurs on most observation days. Condensation is more likely to occur when the soil moisture content is less than 7%.
The cumulative soil condensation quantity and number of condensation days for loess were greater than those for sandy soil under the same soil moisture conditions. Previous studies have shown that the mechanical composition of soils, such as particle size, plays a role in determining the quantity of condensation water. The smaller the soil particle size, the greater the quantity of condensation water [69,70,71,72]. Loess has a much smaller average particle size than sandy soil. Smaller particle sizes result in larger capillary rise heights and high water storage capacities between pores. Furthermore, because of its smaller particle size, loess has a larger specific surface area for water than sandy soil, resulting in a greater water adsorption capacity [37,73,74,75,76].

3.3. Correlation of Soil Condensation Water in Loess and Sandy Soil

In order to analyze whether the characteristics of soil condensation water in soil with different levels of soil moisture content are consistent, the correlation of condensation water under different soil moisture content conditions was determined using the Pearson correlation coefficient method. The results are shown in Table 2. The two adjacent treatments showed the strongest correlations. The correlation between soil condensation quantities in loess under different soil moisture content conditions was significant; the highest correlation coefficient was observed between 3% and 7% moisture content conditions, with a correlation coefficient of 0.895. For sandy soil under different soil moisture content conditions, the correlation between 0% and 11% or 15% moisture content was insignificant. The correlation between 3% and 15% moisture content was not significant, whereas the relationships among the other moisture content conditions were significant. The highest correlation was observed between the 11% and 15% moisture content, with a correlation coefficient of 0.691. According to Table 2, there is a strong correlation between adjacent soil water content groups. Next, we can analyze the average amount of condensation in loess and sandy soil under different soil water content conditions.
The soil moisture content and average condensation quantity with each treatment of loess and sandy soil are shown in Figure 7. The average soil condensation quantity in both loess and sandy soil showed a significant negative correlation with soil moisture content (loess: W = −2.443θ + 0.240, R2 = 0.790, p < 0.05; sandy soil: W = −10.366θ + 0.296, R2 = 0.975, p < 0.05). The higher the soil moisture content, the smaller the quantity of condensation water. When the moisture content was at least 7%, the soil appeared to evaporate on most of the observed days. These results indicate that a lower soil moisture content is more favorable for an increase in the quantity of soil condensation water. This is because the higher the soil moisture content, the larger the soil matrix potential, and a higher soil matrix potential is more conducive to evaporation [77,78].

3.4. Influencing Factors

High soil moisture content may impede soil adsorption and condensation [79]. Both loess and sandy soil only exhibited noticeable condensation of water under 0% and 3% moisture content conditions. Therefore, the following analysis primarily focuses on factors impacting condensation water at 0% and 3% moisture content.

3.4.1. Atmospheric Relative Humidity

The soil condensation quantity and atmospheric relative humidity (RH) at 0% and 3% moisture content in loess and sandy soil are shown in Figure 8. There was a significant positive correlation (p < 0.05) between soil condensation water and RH in both soils under 0% and 3% moisture content conditions. For the same soil moisture content, the slope of the regression equation for sandy soil was greater than that for loess, indicating that the response of sand condensation to RH was more pronounced. For a soil, the correlation coefficient with 0% soil water content was greater than that with 3% soil water content, indicating that the response of low soil water content to RH was more pronounced. In either soil type, the soil condensation quantity increased significantly with an increase in RH under conditions of 0% or 3% moisture content. The atmospheric temperature provides the driving force for condensation and is a crucial factor in dew formation, whereas the RH serves as a necessary source of water vapor for condensation [80,81]. Monteith indicated that soil condensation occurs when the temperature of the condensation surface is lower than the dew point temperature, and that condensation does not necessarily require an RH of 100% [82]. In this study, soil condensation water formed primarily when the RH exceeded 60%. When the air contains more moisture, formation of soil condensation water is promoted. Castillo et al. [22] indicated that the condensation rate on soil surfaces significantly increased with increasing RH within the range of 30% to 80%. This trend aligns with the findings of this study regarding the relationship between soil condensation quantity and RH. In addition, an increase in RH results in more water vapor, which can supply more water for condensation.

3.4.2. Differences between Air Temperature and Dew Point Temperature

The soil condensation quantities and differences between air temperature (Ta) and dew point temperature (Td) at 0% and 3% moisture content in loess and sandy soil are shown in Figure 9. There was a negative correlation between soil condensation water and air temperature–dew point temperature differences (p < 0.05).
For the same soil moisture content, the absolute value of the slope of the regression equation for sandy soil was greater than that for loess, indicating that the response of sand condensation to the differences between air temperature (Ta) and dew point temperature (Td) was more pronounced. For a soil, the correlation coefficient with 0% soil water content was less than that with 3% soil water content, indicating that the response of low soil water content to the differences between air temperature (Ta) and dew point temperature (Td) was more pronounced. Soils with 0% moisture content in Figure 9a,c show higher intercepts than that in Figure 9b,d, respectively, which indicates greater condensation for soils with low moisture content at the same air temperature–dew point difference.
With a constant soil moisture content, a smaller air temperature–dew point difference (Ta-Td) led to a greater quantity of soil condensation water in both soils, especially when Ta-Td was less than 8 °C. As the air temperature–dew point difference exceeded 8 °C, the frequency of soil condensation water generation decreased gradually. This finding is consistent with those of other researchers [23,83,84,85]. In either soil type, the degree of correlation between soil condensation water and Ta-Td at 0% moisture content was greater than that at 3% moisture content, indicating that the lower the soil moisture content, the stronger the influence of the air temperature–dew point difference on the soil condensation quantity. Previous studies have shown that water condensation mainly occurs when the temperature dew point difference is less than 0 [15,86,87]. During the observation period, the surface temperature remained consistently higher than the dew point temperature, similar to what has been observed in previous studies [88]. Previous research [89,90] has suggested that, in such cases, it is not condensation that occurs; rather, it is soil adsorption.

4. Conclusions

The soil condensation volumes of loess and sandy soil were measured under different gravimetric moisture content conditions in the autumn of 2022 and spring of 2023 using hand-made micro-lysimeters and the weighing method at the groundwater and environmental sites of Chang’an University, Guanzhong Basin, China. The following conclusions can be drawn:
(i)
Under the same soil moisture conditions, the amount of condensation and the number of days of condensation for loess are greater than those for sand because loess pores, which are smaller than sand pores, have a larger specific surface area, resulting in a higher adsorption capacity for water.
(ii)
The average soil condensation quantity (W) in loess and sandy soil showed a significant negative correlation with the gravimetric moisture content (θ). For loess, the regression model can be described as follows: W = −2.443θ + 0.240 (R2 = 0.790, p < 0.05); and for sandy soil, the regression model can be described as follows: W = −10.366θ + 0.296 (R2 = 0.975, p < 0.05).
(iii)
Soil condensation water quantities were positively correlated with RH and negatively correlated with air temperature–dew point differences. Soil condensation predominantly occurs under conditions with an RH above 60% and air temperature–dew point differences less than 8 °C.

Author Contributions

Conceptualization, Z.J. and C.J.; methodology, C.J., Z.J. and G.L.; software, C.J. and G.L.; validation, C.J., Z.J., G.L., L.Z. and Y.R.; investigation, C.J., G.L., L.Z. and Y.R.; writing—original draft preparation, C.J. and Z.J.; writing—review and editing, C.J., Z.J., G.L., L.Z. and Y.R. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the Fundamental Research Funds for the Central Universities, CHD (300102293209), the National Natural Science Foundation of China (42001033), and the Natural Science Basic Research Plan in the Shaanxi Province of China (2021JQ-237).

Data Availability Statement

The original contributions presented in the study are included in the article material. Further inquiries can be directed to the corresponding author.

Conflicts of Interest

Author Yuze Ren was employed by the company China Certification & Inspection Northwest Ecological Technology (Shaanxi) Co., Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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Land 13 00934 g001
Figure 1. Geographical location of the experiment site.
Figure 1. Geographical location of the experiment site.
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Figure 2. Schematic diagram of the micro-lysimeter devices (a) and field layout (b).
Figure 2. Schematic diagram of the micro-lysimeter devices (a) and field layout (b).
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Figure 3. Variations in rainfall and atmospheric relative humidity (RH) over the monitoring period.
Figure 3. Variations in rainfall and atmospheric relative humidity (RH) over the monitoring period.
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Figure 4. Trends in near-surface—atmospheric temperature, soil temperature at 1 cm below ground, and dew point temperature during the monitoring period.
Figure 4. Trends in near-surface—atmospheric temperature, soil temperature at 1 cm below ground, and dew point temperature during the monitoring period.
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Figure 5. Daily condensation quantities in loess (a) and sandy soil (b) under different soil moisture content conditions during the monitoring period.
Figure 5. Daily condensation quantities in loess (a) and sandy soil (b) under different soil moisture content conditions during the monitoring period.
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Figure 6. Condensation quantity (a) and condensation days (b) for loess and sandy soil.
Figure 6. Condensation quantity (a) and condensation days (b) for loess and sandy soil.
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Figure 7. Correlation between condensation water and soil moisture content in (a) loess and (b) sandy soil.
Figure 7. Correlation between condensation water and soil moisture content in (a) loess and (b) sandy soil.
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Figure 8. The relationship between daily soil condensation quantity and RH at 0% and 3% moisture content in loess and sandy soil: (a) loess at 0% moisture content; (b) loess at 3% moisture content; (c) sandy soil at 0% moisture content; and (d) sandy soil at 3% moisture content.
Figure 8. The relationship between daily soil condensation quantity and RH at 0% and 3% moisture content in loess and sandy soil: (a) loess at 0% moisture content; (b) loess at 3% moisture content; (c) sandy soil at 0% moisture content; and (d) sandy soil at 3% moisture content.
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Figure 9. The relationship between soil condensation quantity and air temperature–dew point differences at 0% and 3% moisture content in loess and sandy soil: (a) loess at 0% moisture content; (b) loess at 3% moisture content; (c) sandy soil at 0% moisture content; and (d) sandy soil at 3% moisture content.
Figure 9. The relationship between soil condensation quantity and air temperature–dew point differences at 0% and 3% moisture content in loess and sandy soil: (a) loess at 0% moisture content; (b) loess at 3% moisture content; (c) sandy soil at 0% moisture content; and (d) sandy soil at 3% moisture content.
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Table 1. Particle size distribution of soils (units: %).
Table 1. Particle size distribution of soils (units: %).
Soil TypeSand ParticlesSilt ParticlesClay Particles
2–1 mm1–0.5 mm0.5–0.25 mm0.25–0.1 mm0.1–0.05 mm0.05–0.02 mm0.02–0.002 mm0–0.002 mm
Loess0008.3341.7042.687.290
Sandy soil12.0124.7335.1912.751.814.318.800.39
Table 2. Correlation of condensation quantity in loess and sandy soil with different levels of soil moisture content.
Table 2. Correlation of condensation quantity in loess and sandy soil with different levels of soil moisture content.
Soil TypeSoil Moisture Content0%3%7%11%15%
Loess0%1
3%0.530 *1
7%0.527 *0.895 *1
11%0.505 *0.888 *0.893 *1
15%0.491 *0.781 *0.870 *0.871 *1
Sandy soil0%1
3%0.669 *1
7%0.336 *0.638 *1
11%−0.0400.293 *0.583 *1
15%−0.0270.2100.352 *0.691 *1
Note: * indicates the use of a two-tailed significance test, with a significant correlation observed at the 0.05 significance level.
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Jin, C.; Jia, Z.; Li, G.; Zhao, L.; Ren, Y. Effect of Soil Moisture Content on Condensation Water in Typical Loess and Sandy Soil. Land 2024, 13, 934. https://doi.org/10.3390/land13070934

AMA Style

Jin C, Jia Z, Li G, Zhao L, Ren Y. Effect of Soil Moisture Content on Condensation Water in Typical Loess and Sandy Soil. Land. 2024; 13(7):934. https://doi.org/10.3390/land13070934

Chicago/Turabian Style

Jin, Cheng, Zhifeng Jia, Ge Li, Lingke Zhao, and Yuze Ren. 2024. "Effect of Soil Moisture Content on Condensation Water in Typical Loess and Sandy Soil" Land 13, no. 7: 934. https://doi.org/10.3390/land13070934

APA Style

Jin, C., Jia, Z., Li, G., Zhao, L., & Ren, Y. (2024). Effect of Soil Moisture Content on Condensation Water in Typical Loess and Sandy Soil. Land, 13(7), 934. https://doi.org/10.3390/land13070934

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