Experimental Study of Vegetative Properties in Zeolite–Biochar-Improved Ecological Revetment Substrates

Abstract

The vegetation of the ecological substrate plays a crucial role in restoring shoreline ecology. This study focused on using zeolite and biochar as substrate modifiers, specifically utilizing the Cynodon dactylon from Central China for vegetation. A pot vegetation experiment was carried out to compare the effects of different ratios of zeolite and biochar. The vegetation indices, including germination index, plant height, and coverage rate, were analyzed and discussed. The results revealed that zeolite primarily influenced the germination index of Cynodon dactylon, while biochar had a more significant impact on germination percentage, germination energy, plant height, and coverage rate. This study discovered that the seed germination effect of the improved substrate initially increased with zeolite content and then decreased. The average germination percentage was 63.96%. Conversely, it decreased with an increase in biochar content, resulting in an average germination percentage of 55.45%. Zeolite and biochar caused a decrease and increase in substrate pH by −0.11 and 0.4 on average, respectively. The germination of each substrate showed a negative correlation with pH. Additionally, the average coverage and plant height decreased with an increase in biochar content. However, the inclusion of 6% zeolite led to an increase in coverage and plant height. Specifically, the average plant height increased by 3.92 cm and the coverage by 7.48%. Our research identified the optimal ratio of zeolite and biochar as 6% zeolite and 0% biochar, showcasing good overall vegetative properties. These findings offer insights for further understanding the vegetative effects of zeolite–biochar-modified substrates and optimizing substrate schemes for ecological vegetation projects.

1. Introduction

With rapid economic and social development, the population density along riverbanks has increased, leading to unprecedented pollution pressure on riparian zones and water environments. This pollution is primarily caused by agricultural activities, industrial discharge, and urbanization [1,2,3]. During rainfall or irrigation, a large number of pollutants are carried by runoff directly into river bodies, harming the natural functions of aquatic ecosystems and impacting the overall system’s health and stability [3,4,5]. Consequently, effective control and management of non-point source pollution is essential to safeguard water quality and ecological safety, and promote sustainable social development.

Non-point source pollution, the primary cause of riparian water pollution, differs from point source pollution due to its widespread and dispersed origins. This type of pollution primarily results from atmospheric, surface, and underground pollutants being carried into rivers, lakes, reservoirs, and oceans by rainfall [6,7]. Ecological bank protection technology is a crucial strategy for preventing non-point source pollution and safeguarding ecological environments. Currently, it is a focal point of research in the applied science field [8,9]. At present, traditional shoreline protection is mainly based on hard revetment (dry block stone, slurry block stone, etc.), which lacks ecological effect. However, ecological revetment can not only strengthen the landscape function of the bank slope and enhance its stability and erosion resistance [10] but also effectively intercept and purify various non-point source pollutants [11]. Moreover, it can effectively control the leaching of heavy metal pollution from soil compartments, which is an important measure to solve the problem of non-point source pollutants on the bank [12,13,14]. As a mainstream measure for bank slope ecological restoration, ecological substrate revetment mainly consists of soil, bonded material, pH regulator, organic matter, plant seeds, etc. This measure can not only quickly establish vegetation but also improve the stability of the bank slope, purify water, and promote the improvement of the ecosystem [15,16]. In response to the limitations of conventional revetment substrates in addressing non-point source pollution, both domestic and international researchers have conducted numerous studies on enhancing and selecting ecological revetment filler materials. Sun et al. [17] enhanced EPC (ecological pervious concrete) for revetment, highlighting its intricate pore structure that facilitates water infiltration underground or into rivers while also providing habitats for flora and fauna. Park et al. [18] formulated ecological concrete using artificial zeolite, glass fiber, and silica fume, achieving removal rates of 85.7% for TN and 51.6% for TP in contaminated water. Zhu et al. [19] introduced a novel revetment material comprising BC and Ca(OH)₂, demonstrating that a mass fraction of 25% Ca(OH)₂ and 2% BC exhibited effective removal capabilities for ammonia nitrogen (45%), phosphorus (100%), and heavy metals (≥90%). Chen et al. [20] studied multi-aggregate planting ecological concrete and multi-aggregate filter ecological concrete prepared using adsorption materials as coarse aggregate, and the average removal rates of NH₃-N, TP, and COD reached 76%, 54%, and 51%.

In the field of ecological revetment technology, the combination of two enhanced materials, zeolite (ZL) and biochar (BC), has garnered attention due to its significant impact on water purification and soil enhancement. Abedi et al. [21] conducted a study on a zeolite–biochar (ZL-BC)-modified constructed wetland for wastewater treatment, finding that the removal efficiency of COD, ammonia, phenol, Pb, and Mn by ZL-BC reached up to 99%, with lower nitrous oxide emissions compared to gravel. Ghorbani et al. [22] pointed out that the application of ZL-BC improved soil by increasing micro- and mesopores, and the soil water content was increased by 174% and 303%. The specific surface area and mean weight diameter in soil increased by 171% and 197%, respectively. Additionally, Zheng et al. [23] noted in their research that ZL-BC, as a composite modifier, effectively remediates Cd, Pb, As, and W pollution in soil. Although there has been increasing depth in research on ZL-BC composites for pollution treatment, demonstrating their adsorption and purification capabilities in water bodies, there are relatively few studies on the improvement of ecological substrates, and even fewer reports on the vegetative effects of improved substrates. The synergistic effect of ZL-BC-modified substrates on vegetative properties is still unclear. However, the vegetative effect of riparian revetment substrates plays a crucial role in maintaining regional water resource security and biodiversity [24]. Hence, optimizing the ZL to BC ratio for maximizing benefits in riparian vegetative restoration has emerged as a critical issue that requires attention.

In view of this, ZL and BC were chosen as substrate modifiers in this research. Using Cynodon dactylon (C.d.), a pioneering herb for revetment in central China, as a case study, various ZL-BC ratios were compared to analyze their effects on seed germination, plant height, and coverage of C.d. The study elucidated the synergistic effect of ZL-BC on vegetative properties and determined the optimal ratio of improved substrate for plant growth. This research aims to offer a theoretical foundation for selecting substrate schemes in ecological bank protection engineering.

2. Materials and Methods

2.1. Experiment Design

In order to study the impact of ZL- and BC-modified substrate on plant growth and enhance the ecological protection of bank slopes, an outdoor pot experiment was carried out at the Key Laboratory of Intelligent Health Perception and Ecological Restoration of Rivers and Lakes, Ministry of Education, in Wuhan, Hubei Province (30°29′ N, 114°18′ E, approximately 30 m above sea level). The experiment focused on the growth of C.d., a herbaceous plant commonly found in central China.

2.1.1. Experiment Materials

The riverbank ecological substrate, improved with a synergistic mixture of zeolite and charcoal, is created by combining zeolite (ZL), biochar (BC), cement, pH regulator, soil, plant seeds, organic material, and water. All substrate raw materials may be seen in Figure 1. The energy spectrum information of the sample at specific points was tested using electron microscope scanning (Zeiss Gemini 300, Jena, Germany). To ensure data accuracy, energy spectrum analysis was conducted at three different points.

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Soil: The soil sample was collected from the backfill of a foundation pit in Wuhan. Laboratory tests confirmed that the soil was clay. Standard procedures were followed to determine the physical properties of the soil: initial moisture content was determined through oven drying at 105 °C, optimal moisture content and maximum dry density were obtained via compaction tests, natural dry density was measured using the ring knife method, and plastic limit and liquid limit were determined using the liquid limit instrument method. Each index was tested three times, and the average value was calculated. The basic parameters of the soil sample are presented in

Table 1. Basic parameters of soil.

Initial Moisture Content	Optimum Moisture Content	Maximum Dry Density	Natural Dry Density	Plastic Limit	Liquid Limit
15.6%	20%	1.75 g·cm−3	1.5 g·cm−3	23%	41%

, while the elemental composition is detailed in

Table 2. Analysis results of substrate surface element content.

Substrate Type	pH	Element Content (%)
		Na	Mg	Al	Si	K	Ca	Fe
Soil	8.13	—	0.76	4.76	92.03	0.82	—	1.64
Zeolite	7.83	9.18	1.33	18.99	64.93	1.24	2.31	2.02
Biochar	9.71	1.02	7.31	23.59	50.27	2.30	2.93	12.58

. Before use, the soil was dried, mashed, and screened by 2 mm.

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Cement: P.O42.5 grade ordinary Portland cement was selected. The main chemical components include Ca, Si, Al, and Fe. These elements usually exist in the form of CaSiO₃, Ca₂SiO₄, Ca₃Al₂O₆, etc., as bonding materials for the substrate.

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Organic material: The main components were soybean powder, corn meal, fish bone meal, and Chinese medicine residue. These components contain Ca, Fe, P, K, and other minerals, and after natural air drying, were sieved through a 2 mm mesh for reserve.

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pH regulator: The main component was ferrous sulfate, which regulates the alkaline environment generated by cement hydration on the basis of not significantly affecting the strength of the substrate, making it suitable for the survival and reproduction of plants and functional microorganisms.

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Biochar: Plant straw BC was selected and formed by cracking plant straw at 600 °C under low oxygen conditions. It possesses a porous structure and a large specific surface area, resulting in a strong adsorption capacity. Table 2 displays the surface elements of BC for specific cations such as Si, Fe, Al, Na, Ca, K, and Mg, which passed through a 200-mesh sieve.

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Zeolites: Natural clinoptilolite was selected; it is a hydroaluminosilicate mineral, which has the characteristics of a large specific surface area, abundant pores, and many adsorption sites. ZL contains rich cations such as Si, Fe, Al, Na, Ca, K, and Mg, and the specific surface elements are shown in Table 2, which passed through a 200-mesh sieve.

2.1.2. Experimental Process

Based on the relevant literature [25,26] and preliminary test results, the content range of zeolite and biochar was designed at 0%, 1%, 3%, 5%, 7% and 0%, 3%, 6%, 9%, 12% of the overall substrate mass. The sample of ecological revealer substrate was prepared by using fixed cement content and pH regulator content. The specific substrate ratio is shown in Table 2. In this test, there were 5 gradients each for zeolite and biochar, plus a group of pure bare soil samples, resulting in a total of 26 groups of tests.

The planting box was constructed from plastic material measuring 505 × 385 × 140 mm. Each box was partitioned into 6 planting zones, each measuring 165 × 190 × 115 mm. Ecological revealer substrates, varying in ZL and BC content, were blended in specified proportions and placed in the planting zones. Subsequently, the ecological revetment substrate was mixed according to set ratios and applied to the small grid within the planting tank. Prior to this, samples of each substrate were collected and tested for pH using a precise pH meter (PHS-3E). C.d. seeds were evenly distributed across each planting plot (approximately 1500 seeds) based on a planting rate of 20 g/m², followed by regular watering and maintenance. The growth of vegetation was monitored, along with activities such as stirring substrate compaction, watering, seeding, and daily upkeep, as illustrated in Figure 2. Post-seeding, the germination rate of the planting samples was recorded daily for the initial 20 days, while the average plant height was observed and documented every 5 days. On the 90th day, coverage was assessed using image recognition software alongside the collection of temperature and weather data. Figure 3 depicts the curing conditions from days 0 to 40 to 90.

2.2. Determination of Seed Germination and Growth Index

During the germination test, the germination of C.d. was observed and recorded every day until 7 days after the germination was stable, and the germination percentage, germination energy, and germination index were calculated. The calculation formula is as follows:

Germination percentage (GP) = Germination seeds number/Tested seeds number × 100%

Germination energy (GE) = Seeds at the peak of germination number/Tested seeds number × 100%

Germination index (GI) = (Gt/Dt)

where Gt is the germination number in t, and Dt is the corresponding number of germination days.

2.3. Meteorological Data

An automatic meteorological observation station was set up at the pot test site to monitor real-time rainfall, temperature, and other meteorological factors. From April 2023 to July 2023, rainfall and temperature were monitored concurrently, with the results displayed in Figure 4. The average rainfall during this period was 7.4 mm, with a maximum of 70.74 mm occurring on 3 April 2023. The average temperature was 24.35 °C, reaching a high of 32.12 °C on 12 July 2023 and a low of 11.15 °C on 23 April 2023.

3. Results and Analysis

3.1. Effect of Different Substrate Ratios on Seed Germination

3.1.1. Effect on Seed Germination of Cynodon Dactylon

In the study of C.d. seed germination, the addition of ZL and BC had notable impacts on the process. Throughout various stages of the experiment, the effects on seed germination exhibited diverse trends. For detailed information on germination, refer to Figure 5.

During the early stage of germination (days 1–4), varying ratios of ZL and BC did not significantly impact the germination process of C.d. seeds. There was no significant difference in GP between groups, and overall seed germination performance was relatively consistent. The middle stage (5–15 days) emerged as a critical period for rapid seed germination, with the impact of different ecological substrate ratios on GP becoming more pronounced. The presence of ZL and BC actually hindered seed germination during this phase. In the later stage (after the 16th day), seed germination was minimal, and the germination process essentially ceased.

Among the substrates labeled 1# to 26#, the substrate with the highest germination number is 1# with 1129, while the substrate with the lowest germination number is 26# with 595. The average germination number across all substrates was 839. Substrates 1#–6#, 8#–10#, 12#–14#, and 19# exhibited germination numbers higher than the average, while the rest were below. Notably, substrates 11#, 16#, 21#, 22#, 25#, and 26# had GP below 50%. Furthermore, the GP surpassed 60% for substrates 1#, 2#, 3#, 4#, 8#, 9#, 12#, and 14#.

Figure 6 illustrates the impact of different ZL and BC contents on average germination numbers. ZL content ranging from 0 to 12% resulted in average germination numbers of 832, 873, 916, 799, and 717, respectively. The highest germination number was observed at 6% ZL content, showing increases of 9.17%, 4.92%, 14.64%, and 27.75% compared to other ratios. The average GP increased to 6% ZL content, enhancing the vegetative effect of the substrate. However, beyond 6% ZL content, the GP declined rapidly, inhibiting the vegetative effect. On the other hand, increasing BC content from 0 to 7% led to average germination numbers of 959, 840, 860, 779, and 700, respectively. The highest germination number was achieved at 0% BC content, exhibiting increases of 14.16%, 11.51%, 23.10%, and 37% compared to other ratios. Generally, the addition of BC hindered the vegetative effect of the substrate, with noticeable inhibition at content levels above 3%.

3.1.2. Effect on the Germination Characteristics of Cynodon Dactylon Seeds

According to the findings presented in Figure 7, varying ratios of BC and ZL had notable impacts on the GE and GI of C.d. seeds. The average GE exhibited a general decrease with increasing BC content, while it initially increased and then decreased with increasing ZL content. Specifically, the average GE was 8.01 at 0% BC content and 5.28 at 7% BC content. A comparison with other ratios revealed that the average GE at 0% BC content was higher by 44.84%, 19.2%, 39.79%, and 51.7%, respectively. These results indicate that higher levels of BC may impede the germination of C.d. seeds. However, at 3% BC content, the GE was relatively high, suggesting that a moderate addition of BC could mitigate its inhibitory effects. Furthermore, at a ZL content of 3%, the average GE was 7.31, while at 12% ZL content, it was 5.52. A comparison with other ratios showed that a ZL content of 3% resulted in increases of 26.03%, 6.1%, 26.91%, and 32.43%, respectively. In conclusion, a ZL content of 3% demonstrated the most significant enhancement of GE for C.d. seeds.

The average GI decreased with increasing BC content and initially increased before decreasing with increasing ZL content. The highest average GI of 813.85 was observed at 0% BC content, while the lowest of 700.77 was recorded at 7% BC content. Compared to other ratios, a BC content of 0% saw increases of 0.41%, 4.02%, 13.36%, and 16.14%, respectively, indicating that high BC content may negatively impact C.d. seed germination. However, at a BC content of 1%, the GI was similar to the no-addition state, suggesting that low BC content has minimal impact. For ZL content, an average GI of 872.15 was observed at 6% and 644.01 at 12%. A ZL content of 6% showed increases of 10.37%, 6.76%, 24.19%, and 35.42% compared to other ratios, indicating a significant effect on C.d. germination. Beyond 6% ZL content, there was a rapid decrease in GI with a noticeable inhibitory effect. Overall, the impact of BC content on C.d. seed GE was more pronounced, while the effect of ZL content on the GI was more prominent.

3.1.3. Relationship between Seed Germination and Substrate pH

In the study of C.d. seed germination, it was observed that varying ratios of ZL-BC amendments had notable impacts on substrate pH levels, showing a correlation with germination characteristics. Figure 8 illustrates that with the addition of ZL, the pH of the substrate showed a downward trend, and with the addition of BC, the pH of the substrate showed an upward trend. Furthermore, the increase in BC had a more significant effect on the pH of the substrate. Among the substrates labeled 1# to 26#, the pH ranged from 8.13 for 1# (plain soil) to 11.05 for 26# (12% ZL + 7% BC). Specifically, a 3% cement addition increased the substrate pH by 1.44 units. The average pH values for different ZL contents were 9.57, 9.56, 9.62, 9.42, and 9.22, respectively, indicating a gradual increase in pH with ZL content. Similarly, different BC contents showed average pH values of 9.57, 9.57, 9.43, 9.89, and 11, with 1% and 3% BC having minimal impact on pH, while 5% and 7% BC led to a significant pH increase. A 3% increase in ZL content raised the pH by 0.08 on average, whereas a 2% increase in BC content raised the pH by 0.36 on average. Under the same content, the effect of BC on pH value exceeds that of ZL, and the influence of BC is 6.7 times that of ZL.

The analysis presented in Figure 9 demonstrates varying degrees of linear correlation between pH and different seed germination indices. It is evident that the GP, GE, and GI all exhibit a decreasing trend with increasing pH levels. The coefficient of determination (R2) serves as an indicator of the strength of the relationship between the variables, with p-values greater than 0.05 signifying statistical significance. Specifically, both GP and GI display a significant negative correlation with pH, as evidenced by R2 values of 0.532 and 0.639, respectively, with both p-values below 0.05. The GP reflects the ratio of seeds capable of germination, while the GI encompasses both the speed and uniformity of germination. The decline in these two indices clearly highlights the substantial inhibitory impact of unfavorable pH conditions on seed germination. Conversely, the linear fit between GE and pH reveals a small R2 value of 0.114 and p > 0.05, indicating the absence of a significant linear relationship. This suggests that GE, which primarily reflects seed germination vigor, is less influenced by pH levels.

3.2. Analysis of the Effect of Substrate Ratio on Plant Growth

3.2.1. Plant Growth Rules of Different Substrates

When analyzing the effects of ZL and BC on the plant height of C.d. seedlings, Figure 10 illustrates the varying average plant height under different ZL and BC contents, as well as different substrate ratios for substrates No. 1#–26#. Common growth patterns were observed across the different substrates. The C.d. growth cycle can be divided into three stages.

In the germination stage (0–30 days), the growth height of the C.d. seedlings was very small and could be ignored. Between the 5th and 10th day after seeding, the C.d. on each substrate began germinating, resulting in small plant heights. Within 30 days after seeding, the maximum growth height did not exceed 3 cm, with an average height of 1.86 cm. The 11# substrate had the lowest seedling growth height at 1.2 cm, while the 1# substrate had the highest at 2.9 cm. No significant effects of ZL and BC on the root height of C.d. seedlings were observed during this stage.

During the growth stage, from 30 to 75 days after seeding, C.d. seedlings as a whole experienced a period of rapid growth lasting approximately 40 days. The timing of this rapid growth varied among seedlings with different substrate numbers. On average, the height of the C.d. seedlings was 16.87 cm, with the tallest and shortest substrates being 4# and 24#, measuring 21.5 cm and 13.5 cm, respectively. This height discrepancy reached 8 cm, demonstrating significant growth changes in all groups. Relative to day 30, the C.d. growth height for substrates 2# to 6#, 7# to 11#, 12# to 16#, 17# to 21#, and 22# to 26# increased by 888.12%, 807.92%, 645.54%, 699%, and 682.18%, respectively. At this stage, the growth height of each substrate group was progressively graded, showing advantages in plant height ratios when BC content was 0% and 1%. Additionally, root height was notably higher when ZL content was at 6%, followed by 3% ZL content.

During the stable stage (75–90 days after seeding), the growth curve of the 1#~26# substrate C.d. seedlings began to smooth out, and the growth fluctuations decreased. While a few scattered groups of substrate seedlings still experienced some rapid growth, this was only temporary. Overall, all groups of C.d. seedlings entered a stable growth stage, with an average growth height of 19.98 cm, representing an 18.43% increase compared to the previous stage. The substrate showed the highest average plant height when the BC content was 1% and the ZL content was 6%.

3.2.2. Analysis of Plant Coverage Rate of Different Substrates

The coverage rate is determined by calculating the projected area of plant stems and leaves on the ground in relation to the substrate. Each substrate’s projected area is measured and divided by the substrate’s total projected area. The analysis shown in Figure 11 indicates that, with the exception of 22#–26#, which had a low coverage rate below 80%, the average coverage rate for other substrates was 92.28%. Substrates 3#, 5#, 8#, and 9# exhibit coverage rates exceeding 95%. This suggests that most substrate ratios tested in this experiment are suitable for ecological revetment. The impact of BC on average coverage outweighs that of ZL, with average coverage decreasing as BC content increases. Notably, a sharp decline in average coverage occurs at a 7% BC content, setting it apart from other ratios. ZL contents of 3% and 6% enhance coverage, but excessive ZL content can impede plant growth.

The experiment observed a potential relationship between plant coverage height and coverage degree. A graph illustrating the coverage rate and growth height curve of substrates 1# to 26# on the 90th day is presented in Figure 12. The graph shows a linear increase in both area coverage and plant growth height. With a significance level of p < 0.05, it is evident that there is a significant relationship between coverage and plant height. This could be attributed to the curvature of the excessively tall C.d. herbs, leading to an increase in the average coverage of the substrate.

3.3. Comprehensive Evaluation of the Vegetative Properties of the Substrate

3.3.1. Two-Factor Variance Analysis of Vegetative Properties

The impact of BC and ZL contents on the vegetative effect of C.d. was assessed through a two-factor variance analysis, as outlined in

Table 3. Substrate ratio scheme.

Substrate Number	Mass Fraction (%)
	Zeolite	Biochar	Cement	pH Regulator	Organic Material
1#	0	0	0	0	7
2#	0	0	3	1.5	7
3#	3	0	3	1.5	7
4#	6	0	3	1.5	7
5#	9	0	3	1.5	7
6#	12	0	3	1.5	7
7#	0	1	3	1.5	7
8#	3	1	3	1.5	7
9#	6	1	3	1.5	7
10#	9	1	3	1.5	7
11#	12	1	3	1.5	7
12#	0	3	3	1.5	7
13#	3	3	3	1.5	7
14#	6	3	3	1.5	7
15#	9	3	3	1.5	7
16#	12	3	3	1.5	7
17#	0	5	3	1.5	7
18#	3	5	3	1.5	7
19#	6	5	3	1.5	7
20#	9	5	3	1.5	7
21#	12	5	3	1.5	7
22#	0	7	3	1.5	7
23#	3	7	3	1.5	7
24#	6	7	3	1.5	7
25#	9	7	3	1.5	7
26#	12	7	3	1.5	7

. The Anova involved degrees of freedom (df), F-value (F), and p-value (p), where the F-value signifies the statistic and the p-value denotes statistical significance. Throughout the analysis, a p-value below 0.05 (p < 0.05) was deemed to indicate a statistically significant difference.

The data analysis presented in Table 3 reveals a clear relationship between the vegetative properties of C.d. and the levels of BC and ZL present, particularly in terms of GP. Specifically, the amount of BC significantly impacted the GP, GE, plant height, and coverage rate of C.d. (p < 0.001), indicating that the quantity of BC added had a decisive influence on these plant growth parameters. Additionally, while the effect of BC on the GI was relatively small (p = 0.022), it remained statistically significant. Furthermore, the presence of ZL had a substantial impact on the GP and GI of C.d. (p < 0.001), underscoring the crucial role of ZL in enhancing the seed germination process, particularly in terms of improving germination speed and uniformity. The influence of ZL content on GE was also noteworthy (p = 0.003), suggesting that the inclusion of ZL positively affected seed vitality. Although the impact of ZL on plant height was not significant (p = 0.258), potentially indicating that plant height was more influenced by the amount of BC added, its effect on coverage rate was still significant (p = 0.009), highlighting the role of ZL in promoting vegetation cover. In conclusion, ZL significantly impacts the GI of C.d., while BC plays a more substantial role in altering GI, GE, plant height, and coverage rate.

The impact of ZL-BC on seed germination in substrates was compared and analyzed. ZL primarily influenced the GI of C.d. seeds by enhancing the soil nutrient balance and water status through ion exchange and water retention properties [27,28]. This created a more favorable environment for the germination of C.d. seeds. Additionally, Mondal et al. [25] highlighted the importance of minerals like potassium and magnesium in ZL for seed germination. On the other hand, BC significantly affected the GP and potential due to its high porosity and large specific surface area, improving soil water retention and air permeability [29,30,31]. While ZL may have limited direct effects on plant height and coverage rate, the enhanced soil conditions indirectly promote plant growth and vegetation coverage by facilitating root expansion and nutrient absorption [32,33]. Conversely, BC has a more direct impact on plant height, as its improved water retention and nutrient environment directly influence plant growth rate and health, aligning with Kang et al.’s [34] findings.

3.3.2. Comprehensive Vegetative Properties Scores

This study focused on analyzing the final germination number, final coverage rate, and growth height on the 90th day as key indicators of plant growth stages. These metrics provide a quantitative measure of how plants respond to environmental conditions. By evaluating the support provided by substrates throughout the germination and growth stages, a comprehensive score was calculated for substrates 1#~26#. This score was based on a weighted average of 40%, 30%, and 30% for the three indicators, resulting in a comprehensive evaluation index of substrate vegetative properties, as illustrated in

Table 4. Two-factor variance analysis of the Cynodon dactylon germination index.

Vegetative Index	BC			CL
	df	F	p	df	F	p
GP	4	21.976	<0.001	4	13.528	<0.001
GE	4	13.175	<0.001	4	6.535	0.003
GI	4	3.880	0.022	4	11.666	<0.001
Plant height	4	13.355	<0.001	4	1.468	0.258
Coverage rate	4	73.842	<0.001	4	4.841	0.009

.

By analyzing the impact of ZL and BC contents on the comprehensive score, certain patterns emerge, as illustrated in

Table 5. Comprehensive evaluation of the vegetative properties of substrates.

Substrate Number (#)	Coverage Rate (%)	Score (A)	Growth Height (cm)	Score (B)	GP (%)	Score (C)	Comprehensive Score
1	94	94	19	81	75	100	92
2	90	90	21	88	69	92	90
3	96	96	22	92	66	87	92
4	100	100	24	100	68	91	97
5	95	95	23	97	60	79	91
6	92	92	24	100	57	76	89
7	94	94	23	97	53	71	88
8	100	100	23	95	63	84	94
9	96	96	20	82	60	80	87
10	93	93	21	86	57	75	86
11	94	94	20	82	47	62	81
12	91	91	20	85	62	83	87
13	92	92	20	82	57	76	84
14	94	94	19	79	65	86	87
15	90	90	19	80	53	71	81
16	88	88	18	76	49	66	78
17	88	88	19	80	50	67	79
18	89	89	20	83	54	72	82
19	90	90	18	74	59	78	82
20	85	85	18	76	50	67	77
21	87	87	18	77	46	61	76
22	73	73	19	80	42	56	70
23	75	75	20	83	51	67	75
24	78	78	17	70	54	71	74
25	79	79	18	73	47	62	72
26	76	76	18	76	40	53	69

. ZL content affects vegetative properties: at 0%, 3%, and 6% ZL content levels, the average comprehensive scores of the substrate were 81.14, 80.00, and 83.83, respectively. This suggests that optimal vegetative properties are achieved at a ZL content of 6%. However, when the ZL content was increased to 12%, the average composite score decreased to 80.00. On the other hand, the influence of BC content on vegetative properties showed a different trend. Starting at 0% BC content, the substrate had the highest average composite score of 92.50. As the BC content increased, the average composite scores gradually decreased to 89.50 (1%), 83.75 (3%), 80.50 (5%), 73.75 (7%), 72.50 (9%), and 70.50 (12%), respectively. In conclusion, a ZL content of 6% positively impacts the vegetative properties of C.d., while deviating from this level leads to a decrease in vegetative properties. Conversely, increasing BC content negatively affects vegetative properties, resulting in a gradual decrease. Therefore, to promote optimal growth of C.d., it is advisable to select a substrate ratio with medium ZL content and low BC content. The ideal ratio for the growth of C.d. was found to be 6% ZL and 0% BC. Furthermore, out of the 26 substrate groups assessed, 17 scored above 80, indicating overall good vegetative properties.

4. Conclusions

This study compared and analyzed the effects of ZL and BC on seed GI, plant height, and coverage rate, revealing the seed germination and plant growth patterns of ZL-BC-improved substrate. The vegetation of each improved substrate was also evaluated through scoring. The main conclusions are as follows:

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The seed germination effect index of the modified substrate was highest at 6% ZL content, and the GP was 68.13%, showing a trend of initially increasing and then decreasing with higher ZL content. With the increase in BC content, the decreasing trend was not obvious when the content was below 3%, and the average GP before 3% was 56.64%. Both ZL and BC had an effect on substrate pH, increasing by −0.11 and 0.4 on average, respectively; the effect of BC was more significant, and the germination of each substrate was negatively correlated with pH.

(2)

The plant height was highest when the ZL content was 6%, followed by 3%. Additionally, plant height showed certain advantages with BC contents of 0% or 1%. The highest average plant height was observed when the BC content was 1% and ZL content was 6%; the average plant heights were 21.12 cm and 19.38 cm, respectively. As for the coverage rate, it decreased with increasing BC content. ZL contents of 3% and 6% can enhance the coverage rate, being 1.29% and 2.42% higher than the average, but excessively high ZL content inhibits plant formation.

(3)

In the comprehensive evaluation, ZL primarily influenced the GI of C.d., whereas BC had a more pronounced impact on the GP, GE, plant height, and coverage rate. When testing the ZL-BC-modified substrate for C.d., 17 out of 26 substrates scored above 80, resulting in good overall vegetative properties, with dominant ratios observed at 6% ZL and 0% BC.