Changes in Soil Moisture Improved by High-Performance Ester Materials under Dry–Wet Cycles

Abstract

The mechanism for improving soil with high-performance ester material is not yet clear, especially changes in soil moisture under dry–wet cycling conditions. Soil moisture is closely related to its ecological performance, which also leads to a lack of scientific bases for the application range, climate conditions, and long-term performance evolution evaluation of high-performance ester materials in ecological restoration. Our research revealed an optimal ratio for the amount of high-performance ester materials that can improve soil moisture and ecological performance under multiple dry–wet cycling conditions. Dry–wet cycling experiments and planting tests were conducted to study the soil moisture improvement mechanism and the changes caused by high-performance ester materials. Changes in the soil’s moisture, EC, and ecological performance were explored. The results indicate that ester materials can effectively improve soil moisture and EC. Even after multiple dry–wet cycles, ester materials can still play an effective role in improving soil moisture and ecological performance. An optimal ratio for the amount of high-performance ester materials was also found. This research reveals the improvement mechanism for ester materials on soil moisture and ecological performance under dry–wet cycling conditions. Our results provide new data and technical guidance for the improvement of soil moisture and ecological restoration by high-performance ester materials.

1. Introduction

Soil moisture determines the amount of water available for plant growth and development. It has a significant impact on plant growth and the soil’s ecological performance [1]. It directly affects the soil’s quality. If soil’s moisture retention is poor, its ecological performance will deteriorate. Soil’s electrical conductivity (EC) is also closely related to its moisture levels and ecological performance [2]. Electrical conductivity [3,4] is an important indicator of inorganic nutrients in a soil’s surface that plants can quickly utilize. It represents the amount of nutrients available in the soil for plant growth, and the magnitude of a soil’s electrical conductivity is also closely related to soil moisture. The more water soil holds, the higher its EC will be [5]. Therefore, improving soil’s water holding capacity plays an important role in improving its ecological performance.

High-performance ester materials can improve soil’s moisture and ecological performance. Shahid [6] improved soil moisture by using super absorbent hydrogel nanocomposites, resulting in a significant increase in soil moisture and plant growth. High-performance ester materials can change soil’s physicochemical properties, increase moisture, improve plant growth conditions, and are environmentally friendly materials [7]. The materials enhance the soil’s water holding capacity and create suitable conditions for plant growth and development [8]. Huang [9] used high-performance ester materials to enhance soil water retention and ecological performance. The study found that the materials can reduce soil moisture evaporation, increase soil moisture, and promote plant growth. A plant’s growth requires not only sufficient water, but also nutrients. To improve soil’s ecological performance, it is necessary to increase its nutrients. Lai [10] found through experiments that high-performance ester materials can increase the number of large aggregates in the soil and thereby enhance the soil’s ability to store nutrients, which can increase the soil’s electrical conductivity. However, the study still lacks a data-based interpretation of conductivity changes. Moreover, whether the improvement of soil conductivity and moisture by the materials weakens after dry–wet cycles has not been fully studied. A large number of studies have clarified the positive effect of ester materials on soil’s moisture levels and ecological performance. However, currently, the changes in soil’s moisture and ecological performance improved by high-performance ester materials under dry–wet cycling conditions are not yet clear, which restricts the wider use of ester materials in soil’s ecological restoration. Soil in nature constantly undergoes moisture absorption and dehumidification cycles, which can lead to changes in its properties. The dry–wet cycle can alter the structure and physicochemical properties of soil, such as its cohesion [11,12]. Destroying the internal aggregate structure of soil can have an impact on the soil’s water characteristics, thereby affecting its moisture levels and ecological performance [13]. To better improve soil’s ecological performance, it is essential to investigate the changes in soil moisture enhanced by high-performance ester materials under dry–wet cycling conditions.

This study investigated changes in soil’s moisture and ecological performance improvement by high-performance ester materials under dry–wet cycling conditions. Dry–wet cycling and planting tests on ester materials to improve soil moisture and ecological performance were conducted. The study aimed to investigate the improvement effect of ester materials on soil’s water holding capacity, electrical conductivity (EC), and ecological performance under dry–wet cycling conditions, and to reveal their mechanism and changes. This article provides new data and technical guidance for the use of high-performance ester materials in the ecological restoration of soil.

2. Materials and Methods

2.1. Materials

The soil used in this study was taken from South China and composed of sandy loam.

The high-performance ester materials used included polymer adhesive material and polymer water-retaining material. Polymer adhesive materials are a nano waterborne adhesive with strong adhesion. The materials will degrade after approximately 2 years, and the degradation products are CO₂ and H₂O [9]. Polymer water-retaining materials have a good water absorption performance. The degradation cycle of the material is 3 years, and it will eventually degrade into CO₂ and H₂O. Polymer water-retaining materials are small white particles [14] that absorb water and expand when the surrounding environment has sufficient water. When the soil is relatively dry and water is scarce, they will contract and slowly release water for plant growth [7]. Moreover, during the process of water absorption and release, polymer water-retaining materials undergo repeated volume expansion and contraction, which improves the structure and porosity of the soil and is beneficial for plant growth.

2.2. Methods and Content

Dry–wet cycles cause a decrease in soil cohesion with a good aggregate structure and the bonding force between soil particles, a collapse of the internal particle structure, and a reduction in soil aggregation [12,15], which consequently leads to a decrease in the soil’s water holding capacity and nutrient composition, including soil moisture, electrical conductivity (EC), and soil’s ecological performance. High-performance ester materials can enhance the bonding force between soil particles, restore good particle structure, improve soil water holding capacity and soil aggregation [10], enhance the ability to store nutrients, increase soil’s EC, and improve soil’s ecological performance, as shown in Figure 1. This study conducted tests combined with numerical analysis to examine the changes in soil moisture and ecological performance from high-performance ester materials under dry–wet cycling conditions.

Dry–wet cycle tests and planting tests were conducted to study improvements in the soil’s water holding capacity, EC, and ecological performance from high-performance ester materials under dry–wet cycling conditions. The water holding capacity and EC of soil correlate with its ecological performance. Plant growth clearly requires sufficient soil moisture, and EC can reflect the fertility of the soil. Planting tests can directly reflect the soil’s ecological performance improvement from high-performance ester materials.

2.2.1. Dry–Wet Cycle Test

The equipment used for this dry–wet cycle test is shown in Figure 2, which mainly included a tray, a modified cutting ring device (as shown in Figure 2a), and a soil moisture EC detection instrument (as shown in Figure 2b). The 200 cm³ modified cutting ring covered the bottom to prevent a large amount of the soil sample from being lost during the dry–wet cycle, and holes were made in the bottom cover to allow the soil to absorb and dehumidify. The required parameters for soil moisture and the EC detector were obtained by inserting a sensor into the soil sample.

200 g of soil samples were taken for each test group, and high-performance ester materials were mixed into the soil according to the designed proportions outlined in

Table 1. Ratios of high-performance ester materials for soil improvement experiments.

Test Group	Water-Retaining Materials (%)	Adhesive Materials (%)	Notes
CK (0)	0	0
1	0.06	0.03	Added water-retaining and bonding materials
2	0.12	0.03
3	0.18	0.03
4	0.06	0.06
5	0.12	0.06
6	0.18	0.06
7	0.06	0.09
8	0.12	0.09
9	0.18	0.09
10	0.06	/	Only added water-retaining materials
11	0.12	/
12	0.18	/
13	/	0.03
14	/	0.06
15	/	0.09
16	Take 3 g of water-retaining material for dry–wet cycle test		Materials not mixed with soil

. After being evenly mixed, the soil samples were filled into the cutting ring. There were total of 16 test groups, including 1 control group (CK) and 15 groups with different material ratios. The soil samples were placed in an oven for drying at 60 °C. Once dry, the test groups were placed in a tray to absorb moisture for 8 h before fully absorbing it. A detector (as shown in Figure 2) was used to test the water holding capacity and EC of each group at three different positions. An average value was taken as the results and the samples were put back into the oven for drying. The next dry–wet cycle was then prepared for and disturbance of the test soil samples was minimized during the test process. A total of 22 dry–wet cycles were conducted in this experiment and corresponding data were tested.

In addition, 3 g of water-retaining material was taken without being mixed with soil and used as test group 16 for the dry–wet cycle test to study the response of the water-retaining material by itself.

2.2.2. Planting Test

In order to study the ecological performance of high-performance ester materials in improving soil, the soil planting test was conducted to study the effects of different material proportions on plants’ germination rates and heights. This was so that the effect of the ester materials in improving the soil’s ecological performance could be clarified. The material proportions for the test are shown in Table 1. The test included one control group CK and nine test groups, consisting of ten groups in total. Based on the results of the dry–wet cycle test, soil with three different wet-dry cycles were used for planting tests, to study the response of high-performance ester materials to dry–wet cycles in improving soil ecological performance. The plant used in this test is pigeonpea. Each group’s soil sample was placed in a planting vessel (as shown in Figure 3), with multiple small holes at the bottom of the vessel, which allowed for water infiltration and loss. Each group was seeded with 10 pigeonpea seeds. The group’s were watered with 50 mL each time; twice in the first 3 days, and once every 3 days thereafter, to simulate a water scarcity situation. The quantities of sprouts and plant’s height were recorded, and the plant’s germination rate was calculated using the following formula. The experiment lasted for a total of 20 days. We set up three replicate tests for each group, and took the average value as the final results.

$$\chi ={\displaystyle \frac{\mathrm{a}}{{\mathrm{a}}_0}}\times 100\mathrm{\%}$$

(1)

where χ—the plant’s germination rate, (%), a—the quantity of sprouts, a₀—the quantity of seeds sown.

3. Results and Discussion

3.1. The Improvement Effect of High-Performance Ester Materials on Soil Water Holding Capacity

The grading curve of the soil sample used in the study is shown in the Figure 4. The steep grading curve means uniform soil particles, poor grading, and possibly unfavorable internal pore structure of the soil, which is not conducive to soil water retention. In order to improve the water holding capacity of the soil, we used high-performance ester materials.

Polymer water-retaining materials can enhance the water retention and storage performance of soil, while polymer adhesive materials can enhance the bonding force between soil particles. Figure 5 shows the improvement effect of high-performance ester materials on soil’s water holding capacity; it can be seen that the water holding capacity of the test group with different material ratios under various dry–wet cycles is improved. Throughout all dry–wet cycles, the water holding capacity of the test group with added materials was higher than that of the control group without added materials. In test groups 1–9 with added materials, it was found that the soil’s water holding capacity increased with the increase of water-retaining materials, indicating that water-retaining materials played a key role in enhancing the soil’s water holding capacity. As the adhesive material increased, the water holding capacity of the soil increased at first, then decreased; the maximum value appeared in test group 6. Test groups 10–12 only contained water-retaining materials, while groups 13–15 only contained adhesive materials. As shown in Figure 5b, it can be seen that both materials can independently improve the soil’s water holding capacity; even after various dry–wet cycles, their water holding capacity is higher than that of the control group CK. As shown in the Figure 5, with the increase of water-retaining materials, the soil water holding capacity also increases. As the adhesive material increases, the soil moisture capacity first increases and then decreases. And from the graph, we found that the ester materials have an optimal ratio in improving soil’s water holding capacity.

To explore the role of high-performance ester materials in improving soil’s water holding capacity, variances in the data from the test’s result were analyzed. Results from the 0th, 4th, 8th, and 20th dry–wet cycle tests of test groups 1–9 were selected for variance analysis, with the added amount of adhesive materials and water-retaining materials used as independent variables and the soil moisture holding capacity as the dependent variable. For variable water-retaining materials, the significance p-values of the F-test analysis of the 0th, 4th, 8th, and 20th dry–wet cycle test data were 0.039, 0.018, 0.043, and 0.039, respectively, all less than 0.05, showing that water-retaining materials have a significant impact on the water holding capacity of soil. For variable adhesive materials, the analysis of the F-test results from the data from the 0th, 4th, 8th, and 20th dry–wet cycle tests show that the significance p-values were 0.07, 0.198, 0.131, and 0.124, respectively, which were greater than 0.05. This analysis showed that adhesive materials do not have a significant impact on soil’s water holding capacity.

Analysis from the test results above revealed that high-performance ester materials can significantly improve soil’s water holding capacity even under various dry–wet cycles. Water-retaining materials play a major role in improving the soil’s water holding capacity, and adhesive materials can also enhance the soil’s water holding capacity to a certain extent. However, excessive adhesive materials can have a negative effect and cause soil compaction, limiting water absorption and the expansion of water-retaining materials. Therefore, there is an optimal ratio of high-performance ester materials for improving soil’s water holding capacity.

3.2. The Improvement Effect of High-Performance Ester Materials on Soil Water Holding Capacity Soil EC

Soil‘s EC also impacts plant growth. High-performance ester materials can improve soil’s EC, as shown in Figure 6 for the improvement effect of the ester materials on soil EC. The results demonstrate that for soil EC in the test groups with different material ratios under various dry–wet cycles, evidently the high-performance ester materials improved the soil EC. Throughout all dry–wet cycles, the EC of the test group with added materials was higher than that of the CK group without added materials. In test groups 1–9 with added materials, it was found that the soil’s EC increased with the increase of water-retaining materials, indicating that water-retaining materials played a key role in improving soil EC, which is consistent with the trend of improving soil moisture capacity. Soil EC is closely related to soil moisture. With the increase of adhesive materials, the soil’s EC showed a slow increasing trend, with a smaller increase compared to the increase brought by water-retaining materials. Combining the observation and analysis from test groups 10–12 (with only water-retaining materials added) and groups 13–15 (with only adhesive materials added), it can be concluded that both water-retaining materials and adhesive materials can improve soil EC, but that the effect of adhesive materials is smaller than that of water-retaining materials.

To explore the role of high-performance ester materials in improving soil’s EC, variances in the data from the test’s result were analyzed. Results from the 0th, 4th, 8th, and 20th dry–wet cycle tests from test groups 1–9 (with two materials added) were selected for variance analysis, with the added amount of adhesive and water-retaining materials as independent variables and the soil sample’s EC as the dependent variable. For variable water-retaining materials, analysis of the F-test results from the data of the 0th, 4th, 8th, and 20th dry–wet cycle tests showed that the significance p-values were 0.003, 0.003, 0.008, and 0.016, respectively, which were less than 0.05, implying that water-retaining materials can significantly affect soil’s EC. For variable adhesive materials, F-test results analysis of the data from the 0th, 4th, 8th, and 20th dry–wet cycle tests showed that the significance p-values were 0.003, 0.041, 0.004, and 0.046, respectively, all less than 0.05, showing that water-retaining materials had a significant impact on the EC of the soil samples. By comparing the p values of variables water-retaining materials and adhesive materials, the analysis revealed that overall, the p value of water-retaining materials was smaller, and their impact on soil EC was more significant than that of adhesive materials.

From the analysis of the test results above demonstrate that high-performance ester materials can significantly improve soil’s EC under various dry–wet cycles. Both water-retaining materials and adhesive materials play a major role in this improvement, but the influence of water-retaining materials is greater.

3.3. Rules of Soil Improvement Using High-Performance Ester Materials under Dry–Wet Cycling Conditions

Dry–wet cyclesweaken the cohesion of soil, reducing the bonding force between soil particles. This leads to a deterioration of soil particle structure and a reduction in aggregation, which consequently leads to a decrease in the soil’s water holding capacity and EC. As shown in Figure 7, high-performance ester materials respond to the dry–wet cycle in terms of soil water holding capacity. It can be seen that as the dry–wet cycle progresses, the soil’s water holding capacity gradually weakens and then levels off, stabilizing around the 10th time. After various dry–wet cycles, the improvement effect of the ester materials weakened, but the test groups with high-performance ester materials always showed stronger water holding capacity than the control group without materials, and the material still performed an improvement effect. As the number of dry–wet cycles increased, the improvement in water holding capacity becomes more pronounced. Water-retaining materials improve the soil’s water holding capacity through their excellent water absorption and storage performance, which means that the soil still has sufficient moisture content after multiple wet–dry cycles. Adhesive materials enhance the bonding force between soil particles, allowing the soil to maintain a stable aggregate structure after multiple dry–wet cycles.

The dry–wet cycle reduces soil cohesion, resulting in a decrease in the number of large soil aggregates, which in turn reduces organic matter in the soil and leads to a decrease in EC. As shown in Figure 8, the response of high-performance ester materials to dry–wet cycles in improving soil EC has been demonstrated. It was observed that after multiple dry–wet cycles, the improvement effect of the ester materials on soil EC weakened. As the dry–wet cycles continued, the soil EC gradually weakened and then stabilized, reaching a stable state after about 10 cycles. However, when comparing the test group with added materials and the control group without added materials after the influence of dry–wet cycles, high-performance ester materials still showed an improvement effect; the EC of the test group with added materials was higher than that of the control group. Adhesive materials can increase the number of large soil aggregates [10], restore a good aggregate structure to the soil, weaken the impact of dry–wet cycles on the soil’s structure, enhance the soil’s ability to store nutrients, increase the soil’s organic matter content, and thus increase the soil’s EC. Soil’s EC is also closely related to soil’s moisture; the more water is dissolved in the soil, the higher the EC.

Due to the effect of high-performance ester materials, the soil had undergone multiple dry–wet cycles and still had sufficient moisture and EC. Adequate water holding capacity is the key to effective plant growth and development, while EC reflects the fertility level of the soil. Therefore, we can infer that high-performance ester materials can improve the soil’s ecological performance.

3.4. Improvement on Soil Ecological Performance from High-Performance Ester Materials

High-performance ester materials can enhance the ecological performance of soil. Soil samples that have undergone 0, 10, and 22 dry–wet cycles were used for planting tests (as illustrated in Figure 9). As shown in Figure 9, these results demonstrate that as the dry–wet cycle progresses, the plant growth conditions of the soil sample become worse. Comparing plant growth after different times throughout the dry–wet cycles in the same test group, it was found that after multiple dry–wet cycles, plants’ germination ratios and heights will decrease. Therefore, in ecological greening applications, it is generally necessary to cultivate loose soil before sowing. However, even after multiple dry–wet cycles, the plants planted in the improved soil samples still had a higher germination ratio and plant height than the CK group without materials. Therefore, high-performance ester materials can improve the germination rate and height of plants and enable the soil to maintain a good plant growth environment after multiple dry–wet cycles. The group with the best growth conditions was always test group 6, which had the highest plant height and germination rate. This soil improvement experiment shows that Test group 6 also had the highest water holding capacity and high EC.

Observing the test groups 1–3, 4–6, and 7–9, it was found from the graph that with a certain quantity of polymer adhesive material mixed, plant germination rates increased as the quantity of polymer water-retaining material added increased; the more polymer water-retaining material mixed, the higher the soil’s moisture content was, which made the soil more conducive to plant sprouting. The plant’s height also increased from the addition of polymer water-retaining materials. As the added quantity of polymer water-retaining materials was invariant, the added quantity of polymer adhesive materials increased the germination rate and plant height, which first increased and then decreased. This indicates that using excessive polymer adhesive materials will have a negative effect on the plant’s germination and growth. Water-retaining materials and adhesive materials interact with each other in soil. Water-retaining materials play a role in increasing soil porosity and permeability. Adhesive materials can also affect the water holding capacity and EC of soil to a certain extent, but excessive adhesive materials can lead to strong soil particle adhesion, limit the expansion and water absorption of water-retaining materials, and lead to soil hardening and solidification.

Based on the above research, a conclusion can be drawn that high-performance ester materials can enhance soil’s water holding capacity and EC, improve the soil’s plant growth conditions, and increase plant’s germination and height. An optimal proportion of the high-performance ester material addition was also found.

3.5. Changes in Soil Moisture and Soil Ecological Performance Improved by High-Performance Ester Materials under Dry–Wet Cycling Conditions

Figure 10 shows the response of polymer water-retaining materials to dry–wet cycles. After four dry–wet cycles, the water absorption performance of the water-retaining materials had decreased to a certain extent, but after multiple dry–wet cycles, the water absorption showed a tendency to stabilize and maintain a high level. It can be inferred that the decrease in water holding capacity and EC of the soil with materials caused by the dry–wet cycle is mainly due to changes in the soil’s structure. After the dry–wet cycle, the soil aggregate structure will undergo irreversible changes. With repeated dry–wet cycles, water softens the connections between soil particles [15], soil cohesion decreases, soil clay content decreases, coarse particles continuously decompose into fine particles, and large aggregates decompose. This is precisely the reason why the dry–wet cycle leads to a decrease in soil’s water holding capacity and EC, and a decrease in soil’s ecological performance.

High-performance ester materials can significantly enhance soil’s moisture and EC under dry–wet cycling conditions. Polymer water-retaining materials can increase soil porosity through expansion and contraction, and the dry–wet cycle will to some extent limit the expansion of water-retaining materials. However, from the test results, it can be seen that water-retaining materials still play key role in increasing soil’s moisture capacity. Polymer adhesive materials can enhance the connection between soil particles, making their aggregates more stable and less prone to decomposition, and increasing the number of soil clay particles. To some extent, adhesive materials weaken the deterioration of soil’s ecological performance caused by the dry–wet cycle process and improve its water holding capacity. Under the combined effect of the ester materials, the soil maintained a stable aggregate structure [10]. Data analysis was conducted on test groups CK and 1–9 (with two materials added), as shown in Figure 7a, to summarize the rules of improving soil moisture and EC using high-performance ester materials under dry–wet cycling conditions. The relationship was determined using the addition of water-retaining materials w, adhesive materials a, and dry–wet cycling times x as independent variables, and soil water holding capacity y₁ and EC y₂ as dependent variables. First, we took the quantity of dry–wet cycles x as the independent variable, and analysis the relationship between the dependent variables y₁ and y₂ for groups 0–9 was as follows:

$$y=A_1\times e^{\left[-{\displaystyle \frac{x}{t_1}}\right]}+y_0$$

(2)

For the water holding capacity y₁, the formula fitting result is in

Table 2. The formula fitting result of water holding capacity y₁.

Test Group	y0	A1	t1	R2
0	29.00	7.41	5.38	0.96
1	34.80	7.36	4.63	0.97
2	35.18	8.31	4.36	0.98
3	35.52	8.74	4.19	0.98
4	34.74	6.08	5.59	0.96
5	36.47	6.73	4.82	0.98
6	38.08	8.39	4.8	0.98
7	35.21	4.56	5.91	0.94
8	35.45	5.96	5.27	0.97
9	36.40	5.96	5.09	0.98

.

For EC y₂, the formula fitting result is in

Table 3. The formula fitting result of EC y₂.

Test Group	y0	A1	t1	R2
0	237.24	140.37	5.04	0.96
1	269.07	144.72	5.139	0.99
2	288.99	148.89	5.54	0.93
3	306.58	149.96	5.62	0.94
4	295.45	148.81	5.38	0.94
5	303.75	150.73	5.45	0.93
6	323.44	153.9	5.56	0.95
7	302.96	151.66	5.43	0.94
8	314.91	153.7	5.5	0.95
9	332.3	155.27	5.56	0.95

.

The added materials for each group were different, so the constant terms of the formula fitting results are different. We calculated the relationship between the material and the constant terms based on the water-retaining material’s quantity w and adhesive material’s quantity of a. For y₁, $y_0=24.8w+29.1a+30.8$, R² = 0.76. $A_1=7.6+15.1w-42.1a$, R² = 0.94; $t_1=5.1-7.4w-13.7a$, R² = 0.83. The formula fitting results were as follows:

$$y_1=\left(7.6+15.1w-42.1a\right)\times e^{\left[-{\displaystyle \frac{x}{5.1-7.4w+13.7a}}\right]}+24.8w+29.1a+30.8$$

(3)

For y₂, $y_0=278.9w+506a+240$, R² = 0.98. $A_1=140.4+39.1w-95.4a$, R² = 0.98; $t_1=5.08-2.4w+1.5a$, R² = 0.82. The formula fitting results were as follows:

$$y_2=\left(140.4+39.1w-95.4a\right)\times e^{\left[-{\displaystyle \frac{x}{5.08-2.4w+1.5a}}\right]}+278.9w+506a+240$$

(4)

In this formula, y₁ is the soil’s water holding capacity, %; y₂ is the soil’s EC, us/cm; w is the amount of water-retaining material added, %; a is the amount of adhesive material added, %; x is the number of dry–wet cycles; and w, a, x ≥ 0.

From the above analysis, it can be seen that under dry–wet cycling conditions, both adhesive materials and water-retaining materials show an improvement effect on soil’s moisture and EC. The fitting formula for moisture and EC show similarity, the soil moisture and EC are closely related, and the EC value is also affected by water holding capacity. In the equation of y₁, the average value of R² corresponding to variable x is 0.97, and the average value of R² corresponding to added materials variable w and x is 0.84. In the formula of y₂, the mean R² of variable x is 0.95, and the average value of R² corresponding to added materials variable w and x is 0.93. It can therefore be inferred that dry–wet cycles and the addition of materials both have a significant impact on soil’s moisture and EC, but that the impact of dry–wet cycles is slightly greater.

From the above test results and data analysis, it can be seen that under dry–wet cycling conditions, the polymer water-retaining materials and adhesive materials increase soil moisture and EC and improve soil ecological performance. Dry–wet cycles can damage the soil with a stable aggregate structure, decrease soil cohesion, and weaken water holding capacity, EC, and ecological performance. Polymer water-retaining materials can improve the soil’s water holding capacity by absorbing water and expanding it. When the soil has sufficient water, the material absorbs water and expands, while when the soil lacks water, it releases water and contracts to supply water to plants, providing good water conditions for plant growth. The increase in water holding capacity also increases the soil’s EC and enhances fertility. The polymer adhesive materials can enhance soil’s structure stability, increase the number of clay particles in the soil, and create new physical and chemical connections between the soil particles. When the connection force between soil particles is enhanced, it results in an increase in the number of soil aggregates and an improvement in the soil particle structure. Therefore, adhesive materials can also enhance the soil’s water holding capacity to a certain extent and improve the soil’s EC.

An optimal proportion for the quantity of high-performance ester materials was found. Water-retaining materials can greatly enhance the soil’s water holding capacity and ecological performance through water absorption and expansion. Adhesive materials can enhance the viscosity of soil particles and the interaction between particles, improving the stability of the soil’s structure. However, strong connection between particles may limit water absorption and the expansion of water-retaining materials and may reduce the porosity and permeability of the soil. Therefore, in practical ecological restoration applications, appropriate material ratios should be selected based on actual conditions and tests. According to our research, the optimum proportion of materials to improve soil moisture and soil ecological performance was test group 6, with the addition of 0.18% polymer water-retaining material and 0.06% polymer adhesive material. This group had the highest water holding capacity, high EC, and the best plant growth situation.

This study explored changes in soil moisture improved by high-performance ester materials under dry–wet cycles. Previous studies have shown that high-performance ester materials can effectively improve soil moisture and ecological performance [6,9]. This article further investigated the mechanism behind ester materials in improving soil moisture, conductivity, and ecological performance through experimental data and numerical analysis. Through the dry–wet cycle experiments, the changes and mechanism of high-performance ester materials in improving soil moisture, conductivity, and ecological performance were explored, making a case for high-performance ester materials to be more widely used in soil ecological restoration.

4. Conclusions

1. This article studied the changes in soil moisture brought about by high-performance ester materials under dry–wet cycling conditions. The materials can effectively enhance soil moisture and EC and improve soil’s ecological performance. Even after various dry–wet cycles, they can still exert excellent improvement effects on soil.

2. High-performance ester materials can weaken the degradation effect of dry–wet cycles on soil structure, while polymer water-retaining materials can maintain soil’s water holding capacity and EC after multiple dry–wet cycles. Adhesive materials enhance the structural stability of the soil, and weaken the impact of dry–wet cycles on the soil aggregate structure. Adhesive materials also enhance soil’s water holding capacity and EC to a certain extent, but their excessive inclusion will limit the effectiveness of water-retaining materials. An optimum proportion for the inclusion of high-performance ester materials was discovered. The optimum material proportion obtained from our research on improving soil’s ecological performance under dry–wet cycling conditions is 0.18% of water-retaining material and 0.06% of adhesive material.

3. The response of soil improvement with different ratios of high-performance ester materials to dry–wet cycles were revealed through our study, providing new and valuable theory and data contributions for the use of high-performance ester materials in soil’s ecological restoration.