Effects of Biodegradable Mulch Films with Different Thicknesses on the Quality of Watermelon Under Protected Cultivation
by
Haikang Zhao
1,
Xidong Wang
3,
Penghui Jin
1,
Jihua Zhou
1,
Yan Wang
3,
Wentao Dong
2,
Huiqing Ren
2,
Bingru Li
2 and
Wenwen Gong
2,*
1
Beijing Agricultural Technology Extension Station, Beijing 100029, China
2
Beijing Municipal Key Laboratory of Agriculture Environment Monitoring, Institute of Quality Standard and Testing Technology, BAAFS (Beijing Academy of Agriculture and Forestry Sciences), Beijing 100097, China
3
Beijing Daxing District Agricultural Environment and Facility Management Service Station, Beijing 102600, China
*
Author to whom correspondence should be addressed.
Agronomy 2025, 15(10), 2336; https://doi.org/10.3390/agronomy15102336
Submission received: 14 August 2025
/
Revised: 23 September 2025
/
Accepted: 3 October 2025
/
Published: 4 October 2025
(This article belongs to the Special Issue Agricultural Innovation in Sustainable and Organic Vegetable Crops Production)
Abstract
Biodegradable mulch films (BDMs) have emerged as a promising alternative to conventional polyethylene (PE) films in modern horticulture, yet the effect of film thickness on crop performance remains inadequately understood. In this study, a two-year field experiment (2023–2024) under protected cultivation was conducted to evaluate BDMs with thicknesses (0.006, 0.008, and 0.010 mm) for watermelon production in Beijing, China. The results showed that all BDMs enhanced soil temperature and moisture compared to bare soil (main effect of mulching, p < 0.05) and significantly influenced soil available nitrogen (p < 0.05), while other soil properties were less affected. Year effects were generally not significant, reflecting the stable microclimatic conditions under hoop-house cultivation. Mechanical property assessments indicated substantial declines in tensile load, tensile strength, and elongation at break after field use, especially for thinner films. Notably, Bio-0.006 and Bio-0.008 significantly improved fruit weight and soluble sugar content relative to PE (p < 0.05), leading to higher yields and better commercial quality. These results suggested that appropriately thin BDMs can satisfy agronomic requirements for watermelon under protected cultivation while minimizing plastic residues, offering a practical basis for optimizing biodegradable film thickness to balance mulching performance, productivity, and environmental sustainability.
1. Introduction
Watermelon (Citrullus lanatus L.) is a globally important horticultural crop and one of the top five most consumed fruits worldwide [1]. This fruit is extensively cultivated in the temperate and tropical regions due to its high consumer demand and nutritional value, with high levels of vitamins B, C, and E as well as minerals such as phosphorus, magnesium, calcium, and iron [2]. These nutrients contribute to various health benefits of watermelon, including antioxidant, anti-inflammatory, and antihypertensive effects [3]. With increasing consumer awareness and improved living standards, global demand for high-quality watermelon is steadily rising. To enhance the productivity and extend the growing season, protected cultivation systems refer to non-open-field systems that provide a sheltered environment compared with open-field conditions, such as plastic greenhouses or hoop houses, have been widely adopted for the cultivation of watermelon [4]. In such systems, plastic mulch films are commonly used to improve soil temperature, retain the moisture in soil, suppress weed growth, and ultimately boost the crop yield [5].
Currently, polyethylene (PE) films are the most widely used plastic mulch films due to their low cost and mechanical resilience [6]. However, these films exhibit extremely low degradability under natural conditions, raising substantial environmental concerns [7,8]. Particularly, the residual fragments of PE gradually accumulate in the soils and break down into microplastics (<5 mm) over time, threatening soil structure, activity of soil microbes, and agroecosystem sustainability [9,10]. These microplastics can persist in the environment for decades, raising concerns regarding long-term agroecosystem health and food safety [8]. Therefore, PE films have become a major focus in soil pollution research.
Biodegradable mulching films (BDMs) have emerged as an eco-friendly substitute for PE films. BDMs are derived from materials, such as polybutylene adipate terephthalate (PBAT), polylactic acid (PLA), or starch blends, and can be decomposed by microbes into water, CO2, and biomass [11]. BDMs are as beneficial as PE in terms of soil warming and moisture retention, without posing a risk of residual plastic accumulation [12,13,14]. In horticultural production, BDMs have been successfully applied in crops such as tomatoes [15,16], maize [17,18], strawberry [19], and melon [20,21], improving soil temperature and moisture regimes, which promote earlier fruiting and increased yield. Additionally, they contribute to reducing plastic pollution and labor costs associated with film removal after harvest [22]. However, the field performance of BDMs can vary significantly depending on the formulation, color, and thickness of the film. In particular, film thickness can affect both the degradation rate and mulching effectiveness of BDMs [23,24]. Previous studies usually tested only a single thickness, often under different crops or cultivation conditions, and some did not even report thickness, making it difficult to draw direct conclusions [15,16,17,18]. Despite growing interest, only a few studies have systematically evaluated the influence of BDM thickness on its mechanical properties and degradation, as well as crop growth. Especially under protected cultivation, where controlled climate may alter the BDM degradation rates, the agronomic performance of BDM films with varying thickness remains underexplored. This research gap limits the development of an evidence-based framework to select optimal film thickness for protected cultivation.
Therefore, the present study aimed to systematically evaluate the effects of BDMs with varying thickness (0.006, 0.008 and 0.010 mm) on the growth, yield, and quality of watermelon, as well as on soil properties under protected cultivation, using PE mulch and bare soil as controls, thereby isolating thickness effects within the same polymer family and a uniform protected cultivation environment. Furthermore, the degradation and mechanical properties of BDMs were also analyzed before and after use in the second growing season. We hypothesized that (i) BDM would enhance early soil warming and moisture retention, but that an optimum thickness exists for maximizing fruit yield and quality under protected cultivation, and (ii) field exposure reduces the mechanical properties of BDMs in proportion to thickness.
2. Materials and Methods
2.1. Study Site and Cultivation Conditions
The experiment was conducted over two consecutive growing seasons (April to June in both 2023 and 2024) in Panggezhuang, Daxing District, Beijing, China (39.619938 N, 116.345431 E). The area has a warm, humid monsoon climate with ample sunlight, an annual average temperature of 11.5 °C, and an annual average precipitation of 568.9 mm. In this experiment, the watermelon was cultivated in a hoop house equipped with an arched structure and film covering, with side ventilation to maintain air circulation. During the experimental period, daytime temperatures inside the hoop house ranged from 25 to 35 °C, while the nighttime temperatures were above 15 °C. The soil at the experimental site is calcareous cinnamon soil with a pH of 7.48. In the 0–20 cm surface layer, the initial physicochemical properties before the 2023 trial were: total organic carbon (TOC) 1.65%, total nitrogen (TN) 0.12%, total phosphorus (TP) 0.13%, alkali-hydrolyzable nitrogen (AN) 455.3 mg kg−1, and effective phosphorus (EP) 201.7 mg kg−1. The 2023 and 2024 trials were conducted in the same field under similar management.
2.2. Experimental Design
The watermelon cultivar used in this experiment was “L600”, which is a compact-type variety widely grown in northern China. The watermelon of this variety features striped, green, thin but crack-resistant skin, with a crisp, sweet, and slightly granular flesh. The crop has a growth cycle of approximately 90 days, with a fruit development period of around 27 days from anthesis to full ripening, which makes it suitable for spring protected cultivation.
The experiment was based on a randomized complete block design with five treatments. Each treatment had three replicative plots. Each replicate plot measured 3 × 5 m (15 m2) and adopted a paired-row planting pattern. Four rows were arranged as two pairs of closely spaced rows (0.5 m apart), separated by a wider inter-row spacing of 2.0 m between the pairs. Plants were spaced at 0.4 m within each row, with approximately 50 plants per plot. Watermelon plants were grown using a vertical trellis system, with stems supported by strings to allow fruits to hang above the soil surface. Before transplanting, basal fertilization was conducted one month in advance by applying fully decomposed organic fertilizer at a rate of 8 m3 per 667 m2 and compound fertilizer (N:P2O5:K2O = 15:15:15) at 50 kg per 667 m2 in planting furrows. Drip irrigation was used throughout the growing season to meet the crop’s water and nutrient requirements, with uniform emitter spacing ensuring even water distribution across plots and similar irrigation volumes applied to all treatments. The five treatment groups were BS, Bio-0.006, Bio-0.008, Bio-0.010, and PE-0.010. The BS group had bare soil with no mulch. In Bio-0.006, Bio-0.008, and Bio-0.010 groups, BDMs were used, with thicknesses of 0.006, 0.008, and 0.010 mm, respectively, covering the range of commercially common options. In the PE-0.010 group, PE mulch film with a thickness of 0.010 mm was used, representing the typical thickness of traditional films. The PBAT-based BDMs and PE film were supported by Shandong Qingtian Plastic Industry Co., Ltd. (Zibo, China). According to the supplier, DBMs were identical in composition except for thickness. All films were black in color, the most commonly used color in practice, and applied to the soil at the beginning of the planting season.
2.3. Soil Sampling and Analysis
Soil temperature and moisture were monitored in 2023 and 2024, using RC-4HC soil sensors (Jiangsu Jingchuang Inc., Xuzhou, China) placed at 10 cm depth in the center of each plot, resulting in three replicates per treatment. Sensors were regularly checked for proper function, and any missing or obviously erroneous data were excluded from analysis. During watermelon harvesting, composite soil samples (0–20 cm) were collected from five random points within each plot and analyzed. The measurements of soil physicochemical properties were based on Chinese agricultural standards: NY/T 1121.6-2006 (TOC) [25], NY/T 1121.24-2012 (TN) [26], NY/T 88-1988(TP) [27], LY/T 1228-2015 (AN) [28], NY/T 1121.25-2012 (EP) [29], NY/T 1377–2007 (pH) [30].
2.4. Assessment of Growth and Quality of Watermelon
In this study, individual fruit weight and soluble sugar content were considered the primary outcomes, while additional growth and quality parameters were also measured. Growth parameters, such as plant height, fruit shape index (length/diameter ratio), and leaf chlorophyll content, were measured at the maturity stage of plant growth [31]. Plant height and fruit shape index were measured manually using a ruler. Leaf chlorophyll content was measured using a SPAD chlorophyll meter (SPAD-502Plus, Konica Minolta Inc., Tokyo, Japan). Each measurement was repeated five times per treatment.
Fruits were harvested at commercial maturity based on the judgment of experienced farmers. To evaluate the yield of watermelon, five watermelon plants were randomly selected from the central area of each plot, resulting in a total of 15 plants per treatment. The fruit weight was recorded using an electronic balance, and the average individual fruit weight was calculated. Based on the average fruit weight and planting density, the plot yield was estimated and then extrapolated to calculate the yield in hectares.
The measured fruit quality traits included soluble sugar content, sugar gradient (the sugar difference between the fruit center and edge, in °Brix), protein content, and vitamin C (VC) content. The soluble sugar content (mg/g) was determined using a plant soluble sugar content assay kit (Suzhou Keming Biotechnology Co., Ltd., Suzhou, China). Sugar gradient (°Brix) was measured using a handheld digital refractometer (LB20T, LB Instruments, Guangzhou, China). The protein content (mg/g) in watermelon was measured by the bicinchoninic acid (BCA) method using a BCA Protein Assay Kit (Solarbio, Beijing, China). Vitamin C content (mg/g) was determined using a Plant Vitamin C ELISA Kit (MEIMIAN Biotech, Wuhan, China). All tests were conducted according to the protocols recommended by the kit manufacturers. All samples were analyzed in triplicate where applicable.
2.5. Analysis of the Degradation and Mechanical Properties of Mulch Films
To monitor and quantitatively assess the field degradation of mulch films, a 50 cm × 50 cm quadrat was set up in each treatment. Photographs were taken after 20, 35, 50, and 70 days of mulching to observe the changes (e.g., cracks, holes, edge curling) of the film in each treatment group.
After harvest, the films were carefully collected from the soil and rinsed. The mechanical properties of unused and used mulch films were tested by following the standard GB 13735–2017 [32] and GB/T 35795–2017 [33] standards. The measurements included both the original (unused) films and films retrieved after the growing season. The evaluated parameters included thickness, tensile load (N), tensile strength (MPa), elongation at break (%), and tear strength (kN/m). Each measurement was repeated at least five times per treatment. All degradation observations and mechanical property measurements were conducted only in the 2024 season due to resource and time constraints.
2.6. Statistical Analysis
Experimental data were analyzed using SPSS Statistics 21.0 (IBM Corp., Armonk, NY, USA). Soil temperature and moisture were evaluated using repeated measures ANOVA, with treatment, time, and year as fixed factors. Soil physicochemical properties, plant growth traits, and fruit quality parameters were analyzed using two-way ANOVA (treatment and year), followed by one-way ANOVA and Tukey’s HSD test (p < 0.05) when appropriate. Mechanical properties of mulch films were based on technical replicates from the same roll and are presented descriptively without statistical testing. Graphs were prepared using OriginPro 2021 (OriginLab Corp., Northampton, MA, USA).
3. Results
3.1. Effects of Different Mulch Films on Soil Properties
Soil temperature and moisture exhibited pronounced temporal dynamics throughout watermelon growth in both years (Table 1 and Table 2). Repeated-measure ANOVA showed significant effects of treatment (p < 0.01) and time (p < 0.001), as well as a significant treatment × time interaction (p < 0.05). In contrast, the effect of year and its interactions were not significant (p > 0.05), suggesting that the relative differences among treatments were consistent across the two growing seasons. Because the experiment was conducted under protected cultivation in hoop houses, interannual climatic variation was minimized, which likely explains the absence of year effects.
Across both years, all mulch films increased soil temperature compared to bare soil (BS), particularly during the early stages after mulching (Table 1). In general, the warming effect generally strengthened with film thickness, with Bio-0.010 and PE producing the highest soil temperatures, followed by Bio-0.008 and Bio-0.006. Notably, Bio-0.008 and Bio-0.010 provided higher soil temperatures than Bio-0.006, especially at the later stages after mulching. These trends persisted throughout the growth cycle.
Soil moisture was also significantly affected by mulching and time (p < 0.01), with a significant mulching × time interaction (p < 0.05). PE consistently maintained the highest and most stable soil moisture levels throughout the growing season. Among BDMs, Bio-0.010 retained more moisture than Bio-0.008 and Bio-0.006. In particular, Bio-0.006 treatment resulted in a noticeable decline in soil moisture compared to thicker BDMs and PE as the time progressed (40–60 days), suggesting earlier degradation or reduced barrier function.
Mulching treatments had limited effects on soil pH, TOC, TP, and TN, as no significant differences were observed among different treatment groups (p > 0.05; Table 3). In contrast, soil AN was significantly affected by treatment (p < 0.01), while year and the treatment × year interaction were not significant (p > 0.05), indicating that treatment effects were consistent across the two growing seasons. Compared with BS, all mulched treatments reduced AN, with the reduction being most pronounced under PE, followed by the BDMs. Across the two years, PE decreased AN by approximately 59.2–67.1%, whereas BDMs reduced AN by 38.4–63.7%. Soil EP was also influenced by mulching. Two-way ANOVA showed a significant main effect of Treatment (p < 0.05), but not year or treatment × year (p > 0.05). Post hoc comparisons revealed that only PE consistently decreased EP, with reductions of about 12.1–19.9% relative to BS, while BDMs showed no significant effect on EP in either year.
3.2. Effects of Mulch Films on Watermelon Growth
The effects of mulch films on watermelon growth and yield are presented in Table 4. Two-way ANOVA showed a significant main effect of mulching (p < 0.05) on plant growth, while year and M × Y were not significant (p > 0.05), except for the year effect for plant height (p < 0.05), indicating that mulching effects were consistent across the two seasons.
Plant height did not differ significantly among BDM treatments and BS (p > 0.05), whereas PE mulching promoted taller plants compared to BS. Leaf chlorophyll contents, indicated by SPAD values, were significantly lower under PE and Bio-0.010 compared with BS (p < 0.05), while Bio-0.006 and Bio-0.008 did not differ significantly from BS. Fruit shape index also varied among treatments: Bio-0.006 and Bio-0.008 tended to produce rounder fruits (index values closer to 1.0), which are considered more commercially desirable.
Importantly, all mulching treatments increased the individual fruit weight of watermelon compared to BS (p < 0.05). The heaviest fruit was obtained under the Bio-0.006 treatment, with individual fruit weight 29.8–34.5% higher than BS across the two seasons. This corresponded to estimated yields above 52,335 kg/ha compared to 39,660–44,415 kg/ha under BS. Bio-0.008 and Bio-0.010 treatments also produced significantly heavier fruits than BS (p < 0.05), with estimated yields reaching 44,850–48,660 kg/ha, comparable to those under PE.
3.3. Effects of Mulch Films on Nutritional Quality of Watermelon
To evaluate the effects of different mulching treatments on the nutritional quality of watermelon, various fruit quality parameters, such as soluble sugar content, sugar gradient (°Brix difference between fruit center and edge), protein content, and vitamin C (VC) content in the fruit, were measured (Table 5). Two-way ANOVA revealed significant effects of treatment on sugar-related traits (soluble sugar and sugar gradient, p < 0.05), whereas year and treatment × year were not significant (p > 0.05). Protein and VC contents were not significantly affected by mulching (p > 0.05), indicating that mulching mainly influenced sugar-related quality rather than the overall nutritional composition of watermelon.
Across both years, soluble sugar content was higher in fruits grown under Bio-0.006 and Bio-0.008 compared with BS and PE. For instance, Bio-0.006 increased soluble sugar by about 34.0–42.6% relative to BS, with Bio-0.008 showing a similar trend. The sugar gradient, which reflects the uniformity of sweetness between the fruit center and edge, was markedly reduced under Bio-0.006 and Bio-0.008 (<1.7 °Brix) compared with BS (>2.5 °Brix) and PE (>2.3 °Brix), suggesting a more uniform sweetness distribution and potentially improved consumer acceptability. In contrast, no consistent differences in protein or VC contents were observed among treatments across the two years. These findings indicate that mulching mainly influenced sugar-related quality traits rather than the other aspects of fruit nutritional quality.
3.4. Changes in Surface Morphology and Mechanical Properties of Mulch Films After Use
To monitor and quantitatively assess the field degradation of mulch films, a 50 cm × 50 cm quadrat was established in each treatment for regular visual inspection. Photographs taken at 20, 35, 50, and 70 days after mulching during the 2024 growing season are shown in Figure 1. Throughout the growing season, none of the mulch films exhibited visible cracking, tearing, or fragmentation. The surface of all films remained largely intact, with no significant evidence of field degradation during the 70-day observation period. This apparent structural stability, however, does not preclude underlying changes in surface morphology and mechanical properties. Therefore, further characterization was conducted to evaluate the extent of physicochemical alterations induced by field exposure.
To evaluate the field durability of mulch films, the mechanical properties of unused and used films were assessed (Table 6 and Table 7). Before use, all films showed clear thickness-dependent differences in mechanical strength (Table 6). Unused PE showed the highest values of most parameters, while BDMs showed lower values overall. Among BDMs, Bio-0.010 showed the best mechanical performance, including higher tensile load and elongation at break compared with thinner films. In addition, the WVTR values of BDMs increased as film thickness decreased, ranging from 437.7 g·m−2·24 h−1 for Bio-0.010 to 768.0 g·m−2·24 h−1 for Bio-0.006. This trend was consistent with soil moisture data, where thinner BDMs were associated with lower soil water content (Table 6). The higher WVTR of thinner films likely allowed more water vapor to escape from the soil surface, leading to increased evaporative losses and reduced moisture retention.
After use in cultivation, the mechanical properties of BDMs declined substantially (Table 7). The mechanical properties of used Bio-0.006 could not be measured due to excessive fragility during testing, although field observations did not show extensive visible fragmentation or cracking. For Bio-0.008, tensile load and elongation dropped markedly, while Bio-0.010 also exhibited reductions but still maintained relatively higher strength and durability compared with Bio-0.008. In contrast, PE largely preserved its structural integrity, showing only slight decreases in tensile strength and tear resistance. These results demonstrated that BDMs, especially thinner ones, underwent considerable physical changes during cultivation, whereas thicker films better preserved their mechanical functions under field conditions.
4. Discussion
4.1. Mechanical Performance and Degradation Behavior of Mulch Films
The progressive reduction in the mechanical properties of BDMs after use reflected their structural instability under environmental exposure, which was consistent with their intended design for in situ degradation [34,35,36]. In this study, all BDMs showed substantial declines in tensile load, tensile strength, and elongation at break after their use in watermelon cultivation (Table 6 and Table 7). The loss of mechanical strength may be attributed to environmental exposure and microbial activity, which led to the breakdown of polymer chains and structural weakening [37]. The limited degradation of PE film was typical, as PE shows negligible microbial susceptibility due to its highly crystalline nature and the presence of hydrophobic polymer chains with strong C–C bonds. The persistent strength of PE reinforces the need for its manual removal from soil after application and highlights its contribution to plastic residue accumulation in soil over time.
Film thickness plays a critical role in determining the mechanical durability of BDMs. Thicker films (e.g., Bio-0.010) initially exhibited higher tensile and tear resistance and retained more strength than thinner counterparts after application. This finding is in line with previous results observed for PBAT- and PLA-based mulch films [38,39,40,41]. The structural stability of thicker BDMs can be attributed to reduced surface-to-volume ratio and slower penetration of moisture and oxygen, which delayed the onset of the degradation process [38,39]. In contrast, the mechanical properties of the thinnest film (Bio-0.006) could not be tested after use due to extreme brittleness. However, field observations revealed no visible fragmentation of films, suggesting that the thinnest BDM film also maintained functional coverage throughout the cropping cycle. As Cowan et al. [42] noted, visual assessments of mulch films may indicate general deterioration trends of certain mechanical properties. This highlighted an important consideration that the field effectiveness of a mulch film depends on how it behaves under dynamic but less extreme conditions, such as limited UV exposure and stable humidity in the hoop house.
It is also worth noting that the degradation behavior of BDMs does not depend solely on physical thickness but also on polymer composition, crystallinity, and film processing [43]. For instance, films with high PBAT content are usually more ductile initially, but their brittleness may increase faster due to microbial attack [44]. Additionally, additives and fillers can accelerate or inhibit the degradation of mulch films by modifying surface energy and water permeability [43,45]. Unfortunately, such formulation-specific data are rarely disclosed by the manufacturers of commercial products, which limits the direct mechanistic interpretation. These findings highlight the importance of evaluating both lab-based mechanical indices and in-field morphological stability for assessment of mulch performance.
4.2. Integrated Yield and Quality Performance of Watermelon Under Different Mulch Films
Mulching with plastic films is widely regarded as an effective agricultural technique to increase the moisture retention capacity and temperature of soil, thereby optimizing the growth environment for plants [36,46]. Studies have shown the positive impacts of mulching with biodegradable plastic film on the yields of tomato [15,16], maize [17,18], cotton [47], etc. Earlier studies applied BDMs of various thicknesses (e.g., 0.006–0.012 mm), but these were often tested under different crops or environments, limiting direct comparisons [15,16,17,18]. Our study extended this work by isolating thickness effects within the same crop and under uniform protected cultivation.
In this study, all BDMs increased the individual fruit weight of watermelon. Among the tested films, the Bio-0.006 application resulted in the production of the heaviest fruit, with the highest sugar content. Despite becoming the most fragile after application, this film effectively supported the development of plants. These results suggest that, for the protected cultivation of short-cycle crops such as watermelon, high mechanical durability of mulch films beyond the functional period may not be necessary. In fact, moderately degradable films may even facilitate better gas exchange and root-zone oxygenation, as well as alleviate waterlogging by allowing improved soil aeration [18], which explains the higher sugar accumulation observed in thinner BDM treatments. The more pronounced vegetative growth under PE treatment (as indicated by increased plant height) did not translate into higher yield or better fruit quality. In contrast, the restrained vegetative growth under BDM treatments, particularly Bio-0.006 and Bio-0.008, may have favored carbon partitioning toward fruit.
Differences in the fruit shape index across the treatment groups also suggested that thinner BDMs promoted more uniform expansion of fruit. Commercially, round fruits with balanced sugar distribution are often preferred [48]. The fruit shape index closed to 1, and the reduced sugar gradient under Bio-0.006 and Bio-0.008 treatments indicated more synchronized ripening of watermelon. These effects may be attributed to more stable soil conditions, reduced oxidative stress, and better sugar translocation—all largely governed by film permeability and soil thermal dynamics, which together determine both early-season warming and late-season moisture retention [20]. No significant changes were observed in protein or vitamin C contents of watermelon across treatment groups, indicating that the mulch films primarily influenced carbon metabolism rather than overall nutritional composition. This suggested that sugar accumulation (and sugar gradient) tends to be more responsive than vitamin C or protein, likely because sugar metabolism is tightly linked with environmental cues (e.g., temperature, microclimate) and carbon allocation, as supported by a recent study for melon, where mulch-related differences in sugar traits were more pronounced than the differences in secondary metabolites [21].
4.3. Practical Application Prospects and Environmental Implications of BDMs
The mechanical properties of mulch films directly impacted their durability during watermelon cultivation and their environmental footprint after harvest. The mechanical properties of the thinnest BDM (Bio-0.006) could not be tested due to its fragility after use. However, photographic evidence showed that no visible fragmentation was observed in the field, possibly because the protected cultivation environment reduced environmental stress, and the mechanical testing applied stress levels much higher than field conditions. This indicates that despite the significant reduction in tensile strength, the thinnest BDM retained enough physical integrity during the crop cycle to provide effective mulching functions. More importantly, this treatment also led to the highest fruit yield and sugar content, suggesting a favorable balance between degradability and agronomic effectiveness of film. In agricultural practices, the selection of mulch film is based on balanced functional performance, cost, and environmental sustainability [13]. Thinner biodegradable films, such as Bio-0.006, showed limited post-use mechanical strength but still delivered competitive agronomic performance. This suggests that full structural persistence of mulch film is not always necessary, particularly in protected cultivation systems, where soil erosion and mechanical abrasion are minimal.
BDMs can be incorporated directly into the soil after use, where they can be fully mineralized by microbial activity into CO2 and water, thereby saving labor for post-harvest removal and reducing plastic residues and microplastics. These practical benefits are especially relevant in regions facing labor shortages or strict residue management regulations [14]. Unlike PE, which remains largely intact and contributes to long-term soil contamination. Thinner BDMs also offer economic advantages due to lower material costs, and their reduced residual input into the soil makes them more environmentally friendly [49]. However, further research is needed to evaluate the long-term impacts of thin BDMs on soil microbiota, potential accumulation of micro-residues, and compatibility with crop rotation systems.
Therefore, the results of this study suggest that a thinner, moderately degradable film like Bio-0.006 may be an optimal choice for the protected cultivation of crops. It can maintain mulching efficacy during the critical crop development window, undergo sufficient degradation to avoid residue issues, and enhance the yield and quality of fruit. These integrative advantages underscore the importance of optimizing multiple parameters (i.e., mechanical strength, degradability rate, and crop performance) to design and select biodegradable mulch films for sustainable agriculture.
5. Conclusions
In this study, the field performance of BDMs with different thicknesses was systematically evaluated in the protected watermelon cultivation system. All BDMs exhibited a quick decline in mechanical strength after use, especially the thinner films. Still, they remained physically intact in the field and functioned effectively throughout the crop cycle. The thinner films (Bio-0.006 and Bio-0.008) outperformed both thicker BDMs and conventional PE in terms of enhancing individual fruit weight, which corresponded to higher estimated yields, as well as improving sugar content and internal uniformity of sweetness. The results demonstrated that thinner BDMs can improve the fruit yield (essentially representing marketable yield, as all harvested fruits met market standards) and commercial quality of short-cycle crops under protected cultivation conditions. In addition, thinner BDMs require less material, degrade more efficiently, and reduce the labor and pollution costs associated with manual removal of conventional PE films. These findings highlight that thinner BDMs can serve as a viable and sustainable alternative to PE mulching, particularly for the protected cultivation of short-cycle crops. However, it should be noted that optimal BDM thickness may vary with local conditions—including climate, UV exposure, and crop cultivar—and requires validation across multiple seasons. A limitation of this study is that only three replicate blocks were used, direct biodegradation metrics were not measured, and soil microbial/community responses were not assessed. Future studies should further investigate the long-term or seasonal effects of BDMs on soil health, their degradation dynamics under different environmental conditions (e.g., periodic visual inspections, measurement of residual film and microplastic content, and microbial responses), and cost–benefit analysis to promote the rational use of BDMs for sustainable agriculture.
Author Contributions
H.Z.: investigation, methodology, data curation, writing—original draft preparation; X.W.: resources, investigation, project administration; P.J.: investigation, data curation, writing—review and editing; J.Z.: resources, investigation, conceptualization; Y.W.: investigation, data curation; W.D. and H.R.: investigation, data curation, formal analysis, visualization; B.L.: supervision, writing—review and editing; W.G.: conceptualization, supervision, funding acquisition, writing—review and editing. All authors have read and agreed to the published version of the manuscript.
Funding
This research was funded by Special Projects of Construction of Science and Technology Innovation Ability of BAAFS (KJCX20230219), and the China Agriculture Research System (CARS-30).
Data Availability Statement
The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding authors.
Conflicts of Interest
The authors declare no conflicts of interest.
References
- Maoto, M.M.; Beswa, D.; Jideani, A.I. Watermelon as a potential fruit snack. Int. J. Food Prop. 2019, 22, 355–370. [Google Scholar] [CrossRef]
- Mashilo, J.; Shimelis, H.; Maja, D.; Ngwepe, R.M. Meta-analysis of qualitative and quantitative trait variation in sweet watermelon and citron watermelon genetic resources. Genet. Resour. Crop Evol. 2023, 70, 13–35. [Google Scholar] [CrossRef]
- Meghwar, P.; Ghufran Saeed, S.M.; Ullah, A.; Nikolakakis, E.; Panagopoulou, E.; Tsoupras, A.; Smaoui, S.; Mousavi Khaneghah, A. Nutritional benefits of bioactive compounds from watermelon: A comprehensive review. Food Biosci. 2024, 61, 104609. [Google Scholar] [CrossRef]
- Çürük, S.; Sermenli, T.; Mavi, K.; Evrendilek, F. Yield and fruit quality of watermelon (Citrullus lanatus (Thumb.) Matsum. & Nakai.) and melon (Cucumis melo L.) under protected organic and conventional farming systems in a mediterranean region of turkey. Biol. Agric. Hortic. 2004, 22, 173–183. [Google Scholar] [CrossRef]
- Othman, Y.A.; Leskovar, D.I. Degradable mulch as an alternative to polyethylene for watermelon production. HortTechnology 2022, 32, 226–233. [Google Scholar] [CrossRef]
- Li, W.; Yan, W.; Shengnan, W.; Yingchao, Q.; Deng, W.R.; Di, Y.R. Review of Biodegradable Mulching Film Materials. Modern Agr. Res. 2023, 29, 115–118. [Google Scholar]
- Ammala, A.; Bateman, S.; Dean, K.; Petinakis, E.; Sangwan, P.; Wong, S.; Yuan, Q.; Yu, L.; Patrick, C.; Leong, K. An overview of degradable and biodegradable polyolefins. Prog. Polym. Sci. 2011, 36, 1015–1049. [Google Scholar] [CrossRef]
- Gao, H.; Yan, C.; Liu, Q.; Ding, W.; Chen, B.; Li, Z. Effects of plastic mulching and plastic residue on agricultural production: A meta-analysis. Sci. Total Environ. 2019, 651, 484–492. [Google Scholar] [CrossRef]
- Rillig, M.C.; Kim, S.W.; Zhu, Y.-G. The soil plastisphere. Nat. Rev. Microbiol. 2024, 22, 64–74. [Google Scholar] [CrossRef] [PubMed]
- Wang, F.; Wang, Q.; Adams, C.A.; Sun, Y.; Zhang, S. Effects of microplastics on soil properties: Current knowledge and future perspectives. J. Hazard. Mater. 2022, 424, 127531. [Google Scholar] [CrossRef] [PubMed]
- Hu, M.; MIAO, Q.; SHI, H. Mulching effects of different films on soil water, heat and yield of spring maize. Soil 2018, 50, 628–632. [Google Scholar]
- Haider, T.P.; Völker, C.; Kramm, J.; Landfester, K.; Wurm, F.R. Plastics of the Future? The Impact of Biodegradable Polymers on the Environment and on Society. Angew. Chem. Int. Ed. Engl. 2019, 58, 50–62. [Google Scholar] [CrossRef]
- Xiong, L.; Li, Z.; Shah, F.; Wang, P.; Yuan, Q.; Wu, W. Biodegradable mulch film enhances the environmental sustainability compared with traditional polyethylene film from multidimensional perspectives. Chem. Eng. J. 2024, 492, 152219. [Google Scholar] [CrossRef]
- Madin, M.; Nelson, K.; Fatema, K.; Schoengold, K.; Dalal, A.; Onyekwelu, I.; Rayan, R.; Norouzi, S.S. Synthesis of current evidence on factors influencing the suitability of synthetic biodegradable mulches for agricultural applications: A systematic review. J. Agr. Food Res. 2024, 16, 101095. [Google Scholar] [CrossRef]
- Zhang, X.; You, S.; Tian, Y.; Li, J. Comparison of plastic film, biodegradable paper and bio-based film mulching for summer tomato production: Soil properties, plant growth, fruit yield and fruit quality. Sci. Hortic. 2019, 249, 38–48. [Google Scholar] [CrossRef]
- Han, Y.; Lu, L.; Wang, L.; Liu, Z.; Huang, P.; Chen, S.; Li, Y.; Sun, M.; He, C.; Wang, J.; et al. In-situ straw return, combined with plastic film use, influences soil properties and tomato quality and yield in greenhouse conditions. Agr. Commun. 2024, 2, 100028. [Google Scholar] [CrossRef]
- Wang, Z.; Li, M.; Flury, M.; Schaeffer, S.M.; Chang, Y.; Tao, Z.; Jia, Z.; Li, S.; Ding, F.; Wang, J. Agronomic performance of polyethylene and biodegradable plastic film mulches in a maize cropping system in a humid continental climate. Sci. Total Environ. 2021, 786, 147460. [Google Scholar] [CrossRef]
- Yin, M.; Li, Y.; Fang, H.; Chen, P. Biodegradable mulching film with an optimum degradation rate improves soil environment and enhances maize growth. Agric. Water Manag. 2019, 216, 127–137. [Google Scholar] [CrossRef]
- Costa, R.; Saraiva, A.; Carvalho, L.; Duarte, E. The use of biodegradable mulch films on strawberry crop in Portugal. Sci. Hortic. 2014, 173, 65–70. [Google Scholar] [CrossRef]
- Cozzolino, E.; Di Mola, I.; Ottaiano, L.; Bilotto, M.; Petriccione, M.; Ferrara, E.; Mori, M.; Morra, L. Assessing yield and quality of melon (Cucumis melo L.) improved by biodegradable mulching film. Plants 2023, 12, 219. [Google Scholar] [CrossRef]
- Sellami, M.H.; Di Mola, I.; Ottaiano, L.; Cozzolino, E.; del Piano, L.; Mori, M. Evaluation of Biodegradable Mulch Films on Melon Production and Quality under Mediterranean Field Conditions. Agronomy 2024, 14, 2075. [Google Scholar] [CrossRef]
- Akhir, M.A.M.; Mustapha, M. Formulation of biodegradable plastic mulch film for agriculture crop protection: A review. Polym. Rev. 2022, 62, 890–918. [Google Scholar] [CrossRef]
- Amare, G.; Desta, B. Coloured plastic mulches: Impact on soil properties and crop productivity. Chem. Biol. Technol. Ag. 2021, 8, 1–9. [Google Scholar] [CrossRef]
- Moreno, M.; Moreno, A. Effect of different biodegradable and polyethylene mulches on soil properties and production in a tomato crop. Sci. Hortic. 2008, 116, 256–263. [Google Scholar] [CrossRef]
- NY/T 1121.6-2006; Soil Testing-Part 6: Determination of Soil Organic Matter. Ministry of Agriculture of the PRC: Beijing, China, 2006.
- NY/T 1121.24-2012; Soil Testing. Part 24: Determination of Total Nitrogen in Soil. Automatic Kjeldahl Apparatus Method. Ministry of Agriculture of the PRC: Beijing, China, 2012.
- NY/T 88-1988; Soil Total Phosphorus Determination Method. Ministry of Agriculture of the PRC: Beijing, China, 1988.
- LY/T 1228-2015; Nitrogen Determination Methods of Forest Soils. China Standard Publishing House: Beijing, China, 2016.
- NY/T 1121.25–2012; Soil Testing-Part 25: Method for Determination of Available Phosphorus by Continuous Flow Analyzer. Ministry of Agriculture of the PRC: Beijing, China, 2012.
- NY/T 1377-2007; Determination of pH in Soil. Ministry of Agriculture of the PRC: Beijing, China, 2007.
- Sadrnia, H.; Rajabipour, A.; Jafary, A.L.I.; Javadi, A.; Mostofi, Y. Classification and Analysis of Fruit Shapes in Long Type Watermelon Using Image Processing. Int. J. Agric. Biol. 2007, 9, 1. [Google Scholar]
- GB13735—2017; Polyethylene Blown Mulch Film for Agricultural Uses. General Administration of Quality Supervision, Inspection and Quarantine of the PRC: Beijing, China, 2017.
- GB/T 35795-2017; Fully Biodegradable Agricultural Ground Cover Films. General Administration of Quality Supervision, Inspection and Quarantine of the PRC: Beijing, China, 2017.
- Mu, X.G.; Gao, H.; Li, M.-H.; Zhao, X.-R.; Guo, N.; Jin, L.; Li, J.-S.; Ye, L. Effects of Different Types of Plastic Film Mulching on Soil Quality, Root Growth, and Yield. Environ. Sci. 2023, 44, 3439–3449. [Google Scholar]
- Bandopadhyay, S.; Sintim, H.Y.; DeBruyn, J.M. Effects of biodegradable plastic film mulching on soil microbial communities in two agroecosystems. PeerJ 2020, 8, e9015. [Google Scholar] [CrossRef]
- Kasirajan, S.; Ngouajio, M. Polyethylene and biodegradable mulches for agricultural applications: A review. Agron. Sustain. Dev. 2012, 32, 501–529. [Google Scholar] [CrossRef]
- Kyrikou, I.; Briassoulis, D. Biodegradation of Agricultural Plastic Films: A Critical Review. J. Polym. Environ. 2007, 15, 125–150. [Google Scholar] [CrossRef]
- Wu, L.; Zhao, S.; Wang, P.; Yin, B.; Ma, Y.; Zhao, Z. Recovery performance of new plastic mulch films with different thickness. J. China Agric. Univ. 2022, 27, 173–184. [Google Scholar]
- Guo, H.; Yu, X.; Jin, W.; He, N.; Guo, W. Establishment of prediction model for tensile mechanics of plastic film and prediction of film thickness. J. Chin. Agric. Mech. 2020, 41, 173–178. [Google Scholar]
- Zhang, J.; Wang, X.; Zhang, L.; Yu, C.; Jiang, Y.; Zhang, H.; Liu, X.; Qiao, Y.; Wang, X.; Hou, S. Effects of mechanical tensile properties of plastic film on plastic recycling method. Trans. Chin. Soc. Agric. Eng. 2015, 31, 41–47. [Google Scholar]
- Sun, S.; Zhang, W.; Liu, C.; Zhou, J.; Zhu, K. Degradation property of oxo-biodegradable plastic film and its mulching effect on soil moisture, soil temperature and maize growth in rainfed Northeast China. China Chin. J. Eco-Agric. 2019, 27, 72–80. [Google Scholar]
- Cowan, J.S.; Saxton, A.M.; Liu, H.; Leonas, K.K.; Inglis, D.; Miles, C.A. Visual Assessments of Biodegradable Mulch Deterioration Are Not Indicative of Changes in Mechanical Properties. HortScience 2016, 51, 245–254. [Google Scholar] [CrossRef]
- Briassoulis, D. Mechanical behaviour of biodegradable agricultural films under real field conditions. Polym. Degrad. Stabil. 2006, 91, 1256–1272. [Google Scholar] [CrossRef]
- Tokiwa, Y.; Calabia, B.P.; Ugwu, C.U.; Aiba, S. Biodegradability of Plastics. Int. J. Mol. Sci. 2009, 10, 3722–3742. [Google Scholar] [CrossRef]
- Andrady, A.L.; Neal, M.A. Applications and societal benefits of plastics. Philos. T R. Soc. B 2009, 364, 1977–1984. [Google Scholar] [CrossRef]
- Gu, X.-B.; Li, Y.-N.; Du, Y.-D. Biodegradable film mulching improves soil temperature, moisture and seed yield of winter oilseed rape (Brassica napus L.). Soil. Till Res. 2017, 171, 42–50. [Google Scholar] [CrossRef]
- Wang, Z.; Wu, Q.; Fan, B.; Zhang, J.; Li, W.; Zheng, X.; Lin, H.; Guo, L. Testing biodegradable films as alternatives to plastic films in enhancing cotton (Gossypium hirsutum L.) yield under mulched drip irrigation. Soil. Till Res. 2019, 192, 196–205. [Google Scholar] [CrossRef]
- Guo, S.; Tian, R.; Wang, Y. The reviews of sugar accumulation in Watermelon fruits. Chin. Agr. Sci. Bull. 2010, 26, 271–274. [Google Scholar]
- Velandia, M.; Galinato, S.; Wszelaki, A. Economic Evaluation of Biodegradable Plastic Films in Tennessee Pumpkin Production. Agronomy 2020, 10, 51. [Google Scholar] [CrossRef]
Figure 1.
Surface morphology of BDMs during the growing season in 2024.
Table 1.
Effects of mulch films on soil average temperatures (°C) at 10–60 days after mulching in 2023 and 2024.
Table 1.
Effects of mulch films on soil average temperatures (°C) at 10–60 days after mulching in 2023 and 2024.
| Treat. | Days After Mulching | ||||||
|---|---|---|---|---|---|---|---|
| 10 | 20 | 30 | 40 | 50 | 60 | ||
| Year 2023 | |||||||
| BS | 20.1 ± 0.38 | 22.3 ± 0.65 | 23.1 ± 0.82 | 21.8 ± 1.26 | 23.6 ± 0.51 | 24.1 ± 1.06 | |
| Bio-0.006 | 22.5 ± 1.08 | 22.8 ± 0.22 | 24.1 ± 0.64 | 22.5 ± 1.04 | 24.1 ± 0.22 | 25.5 ± 0.36 | |
| Bio-0.008 | 22.7 ± 2.14 | 23.8 ± 0.10 | 24.1 ± 1.71 | 23.3 ± 0.86 | 24.5 ± 0.31 | 26.0 ± 0.88 | |
| Bio-0.010 | 24.1 ± 1.15 | 24.1 ± 0.91 | 25.4 ± 2.01 | 23.7 ± 1.05 | 24.7 ± 0.25 | 26.3 ± 0.57 | |
| PE-0.010 | 24.2 ± 1.31 | 25.2 ± 0.12 | 25.3 ± 0.82 | 23.7 ± 0.84 | 26.2 ± 0.41 | 27.1 ± 0.42 | |
| Year 2024 | |||||||
| BS | 23.3 ± 0.49 | 22.5 ± 0.36 | 22.4 ± 1.15 | 22.1 ± 0.80 | 23.3 ± 0.61 | 25.3 ± 0.55 | |
| Bio-0.006 | 25.7 ± 0.45 | 24.5 ± 0.12 | 24.8 ± 1.11 | 21.7 ± 0.85 | 23.4 ± 0.42 | 25.7 ± 0.45 | |
| Bio-0.008 | 24.7 ± 0.44 | 23.6 ± 0.06 | 23.0 ± 0.70 | 22.7 ± 0.68 | 24.7 ± 0.38 | 26.9 ± 0.60 | |
| Bio-0.010 | 25.1 ± 0.50 | 24.9 ± 0.12 | 23.5 ± 0.68 | 23.7 ± 2.59 | 24.0 ± 0.15 | 26.2 ± 0.35 | |
| PE-0.010 | 25.3 ± 0.56 | 25.5 ± 0.96 | 25.6 ± 1.01 | 24.5 ± 1.78 | 26.5 ± 0.91 | 27.6 ± 0.78 | |
| Significance | |||||||
| Mulching (M) | <0.01 | ||||||
| Time (T) | <0.001 | ||||||
| M × T | <0.05 | ||||||
Note: Data presented here are mean ± standard deviation (n = 3). Because measurements were repeatedly taken over time, no daily significance tests were performed. Instead, repeated-measure ANOVA was used to test the overall effects of mulching, time, and their interaction, with p-values reported below the table. The effect of Year and its interactions were not significant (p > 0.05) and are therefore not shown in the table.
Table 2.
Effects of mulch films on soil average moisture (%) at 10–60 days after mulching in 2023 and 2024.
Table 2.
Effects of mulch films on soil average moisture (%) at 10–60 days after mulching in 2023 and 2024.
| Treat. | Days After Planting | ||||||
|---|---|---|---|---|---|---|---|
| 10 | 20 | 30 | 40 | 50 | 60 | ||
| Year 2023 | |||||||
| BS | 51.0 ± 1.56 | 58.1 ± 1.38 | 60.1 ± 2.81 | 61.9 ± 2.24 | 58.1 ± 0.98 | 64.2 ± 2.01 | |
| Bio-0.006 | 53.2 ± 2.22 | 62.5 ± 2.88 | 66.1 ± 2.58 | 60.5 ± 3.15 | 61.5 ± 2.29 | 63.2 ± 2.87 | |
| Bio-0.008 | 56.3 ± 3.21 | 62.1 ± 1.20 | 67.9 ± 3.24 | 64.9 ± 2.28 | 73.5 ± 3.61 | 75.6 ± 3.19 | |
| Bio-0.010 | 62.3 ± 2.78 | 64.4 ± 2.54 | 70.8 ± 1.89 | 75.2 ± 3.04 | 75.6 ± 3.13 | 74.9 ± 2.52 | |
| PE-0.010 | 65.1 ± 3.15 | 66.3 ± 3.21 | 77.8 ± 2.96 | 76.0 ± 2.47 | 74.4 ± 2.31 | 76.1 ± 2.47 | |
| Year 2024 | |||||||
| BS | 49.9 ± 9.75 | 49.0 ± 1.40 | 49.3 ± 2.32 | 62.1 ± 8.47 | 51.4 ± 3.76 | 63.6 ± 3.30 | |
| Bio-0.006 | 56.4 ± 2.20 | 61.8 ± 1.40 | 64.5 ± 2.55 | 67.0 ± 4.32 | 52.4 ± 0.92 | 63.5 ± 3.80 | |
| Bio-0.008 | 63.9 ± 2.03 | 64.3 ± 3.16 | 69.9 ± 1.83 | 74.8 ± 5.48 | 57.9 ± 1.17 | 64.8 ± 2.04 | |
| Bio-0.010 | 63.5 ± 2.35 | 67.8 ± 3.25 | 73.1 ± 2.97 | 78.4 ± 3.9 | 61.3 ± 2.69 | 70.8 ± 2.32 | |
| PE-0.010 | 66.7 ± 2.86 | 66.9 ± 1.78 | 75.6 ± 2.22 | 80.6 ± 3.59 | 74.6 ± 0.91 | 79.3 ± 1.89 | |
| Significance | |||||||
| Mulching (M) | <0.01 | ||||||
| Time (T) | <0.001 | ||||||
| M × T | <0.05 | ||||||
Note: Data presented here are mean ± standard deviation (n = 3). Because measurements were repeatedly taken over time, no daily significance tests were performed. Instead, repeated-measure ANOVA was used to test the overall effects of mulching, time, and their interaction, with p-values reported below the table. The effect of year and its interactions were not significant (p > 0.05) and are therefore not shown in the table.
Table 3.
Physicochemical properties of soil under treatment with different mulch films in 2023 and 2024.
Table 3.
Physicochemical properties of soil under treatment with different mulch films in 2023 and 2024.
| Treat. | pH | TOC % | TP % | TN % | AN mg/kg | EP mg/kg | |
|---|---|---|---|---|---|---|---|
| Year 2023 | |||||||
| BS | 7.89 ± 0.07 | 1.09 ± 0.13 | 0.16 ± 0.03 | 0.17 ± 0.02 | 396.7 ± 22.2 a | 183.1 ± 15.4 a | |
| Bio-0.006 | 8.02 ± 0.04 | 1.17 ± 0.16 | 0.17 ± 0.02 | 0.15 ± 0.01 | 217.4 ± 20.0 b | 189.5 ± 10.1 a | |
| Bio-0.008 | 8.11 ± 0.10 | 1.45 ± 0.24 | 0.15 ± 0.02 | 0.20 ± 0.03 | 163.3 ± 16.2 c | 201.1 ± 17.3 a | |
| Bio-0.010 | 8.07 ± 0.06 | 1.42 ± 0.17 | 0.14 ± 0.01 | 0.18 ± 0.01 | 170.1 ± 18.7 c | 184.1 ± 11.8 a | |
| PE-0.010 | 8.23 ± 0.12 | 1.15 ± 0.35 | 0.13 ± 0.02 | 0.15 ± 0.01 | 161.8 ± 14.3 c | 146.6 ± 14.1 b | |
| Year 2024 | |||||||
| BS | 7.78 ± 0.02 | 1.12 ± 0.16 | 0.18 ± 0.05 | 0.15 ± 0.02 | 418.3 ± 26.1 a | 179.2 ± 7.8 a | |
| Bio-0.006 | 7.89 ± 0.05 | 1.29 ± 0.26 | 0.15 ± 0.03 | 0.15 ± 0.03 | 230.2 ± 16.6 b | 181.9 ± 12.7 a | |
| Bio-0.008 | 8.13 ± 0.04 | 1.56 ± 0.37 | 0.19 ± 0.01 | 0.17 ± 0.04 | 151.9 ± 40.2 c | 196.8 ± 13.6 a | |
| Bio-0.010 | 7.99 ± 0.11 | 1.34 ± 0.32 | 0.18 ± 0.01 | 0.14 ± 0.03 | 161.3 ± 14.3 c | 179.6 ± 8.7 a | |
| PE-0.010 | 8.27 ± 0.07 | 1.11 ± 0.18 | 0.16 ± 0.02 | 0.12 ± 0.02 | 137.8 ± 4.7 c | 157.6 ± 5.8 b | |
| Significance | |||||||
| Mulching (M) | ns | ns | ns | ns | ** | * | |
| Year (Y) | ns | ns | ns | ns | ns | ns | |
| M × Y | ns | ns | ns | ns | ns | ns | |
Note: Data presented here are mean ± standard deviation (n = 3, plot means). Different letters within each column indicate significant differences among treatments at p < 0.05 according to one-way ANOVA followed by Tukey’s HSD test. Treatments without letters are not significantly different (ANOVA, p > 0.05). ns, *, **: non-significant, and significant per p ≤ 0.05 and p ≤ 0.01 according to two-way ANOVA. TOC, total organic carbon; TP, total phosphorus; TN, total nitrogen; AN, alkali-hydrolyzable nitrogen; EP, effective phosphorus.
Table 4.
Effects of mulch films on watermelon growth in 2023 and 2024.
| Treat. | Plant Height (cm) | Chlorophyll Content (SPAD) | Fruit Shape Index | Individual Fruit Weight (kg) | Estimated Yield (kg/ha) | |
|---|---|---|---|---|---|---|
| Year 2023 | ||||||
| BS | 272.2 ± 12.10 b | 54.21 ± 1.31 a | 1.32 ± 0.03 a | 1.21 ± 0.11 c | 40,365 | |
| Bio-0.006 | 266.1 ± 14.27 b | 57.96 ± 3.74 a | 1.01 ± 0.01 b | 1.57 ± 0.17 a | 52,335 | |
| Bio-0.008 | 281.4 ± 13.71 ab | 57.39 ± 2.69 a | 1.03 ± 0.01 b | 1.46 ± 0.25 ab | 48,660 | |
| Bio-0.010 | 278.5 ± 11.34 b | 48.74 ± 2.50 b | 1.29 ± 0.02 a | 1.35 ± 0.10 b | 44,850 | |
| PE-0.010 | 296.7 ± 13.37 a | 46.80 ± 1.86 b | 1.31 ± 0.03 a | 1.47 ± 0.11 ab | 48,990 | |
| Year 2024 | ||||||
| BS | 276.6 ± 14.03 b | 56.18 ± 1.31 a | 1.31 ± 0.02 a | 1.19 ± 0.12 c | 39,660 | |
| Bio-0.006 | 257.2 ± 16.48 b | 59.46 ± 3.74 a | 1.00 ± 0.02 b | 1.60 ± 0.30 a | 53,325 | |
| Bio-0.008 | 286.0 ± 13.45 b | 57.02 ± 2.69 a | 0.98 ± 0.03 b | 1.45 ± 0.20 ab | 48,330 | |
| Bio-0.010 | 252.6 ± 27.57 b | 49.70 ± 2.50 b | 1.34 ± 0.02 a | 1.45 ± 0.14 ab | 48,330 | |
| PE-0.010 | 313.4 ± 20.53 a | 46.02 ± 0.06 c | 1.30 ± 0.04 a | 1.33 ± 0.16 b | 44,340 | |
| Significance | ||||||
| Mulching (M) | * | * | * | * | - | |
| Year (Y) | * | ns | ns | ns | - | |
| M × Y | ns | ns | ns | ns | - | |
Note: Data presented here are mean ± standard deviation (n = 3, plot means), except for estimated yield. Different letters within each column indicate significant differences among treatments at p < 0.05 according to one-way ANOVA followed by Tukey’s HSD test. ns, *: non-significant, and significant per p ≤ 0.05 according to two-way ANOVA.
Table 5.
Effects of mulch films on the nutritional quality of watermelon in 2023 and 2024.
| Treat. | Soluble Sugar Content (mg/g) | VC Content (μmol/L) | Protein Content (mg/g) | Brix Difference (°Brix) | |
|---|---|---|---|---|---|
| Year 2023 | |||||
| BS | 21.07 ± 2.70 b | 9.21 ± 0.43 | 33.51 ± 2.74 | 2.7 ± 0.32 a | |
| Bio-0.006 | 28.23 ± 1.45 a | 9.08 ± 0.78 | 31.27 ± 4.63 | 1.6 ± 0.24 b | |
| Bio-0.008 | 27.35 ± 1.47 ab | 9.14 ± 1.16 | 34.24 ± 6.33 | 1.7 ± 0.11 b | |
| Bio-0.010 | 25.76 ± 1.81 b | 9.22 ± 0.74 | 36.82 ± 7.12 | 1.9 ± 0.28 b | |
| PE-0.010 | 22.41 ± 2.32 b | 9.19 ± 0.39 | 37.18 ± 2.85 | 2.9 ± 0.47 a | |
| Year 2024 | |||||
| BS | 20.44 ± 2.11 c | 9.16 ± 0.51 | 38.03 ± 5.22 | 2.5 ± 0.25 ab | |
| Bio-0.006 | 29.15 ± 2.90 a | 9.04 ± 1.07 | 32.16 ± 9.07 | 1.7 ± 0.36 b | |
| Bio-0.008 | 27.73 ± 0.98 ab | 9.03 ± 0.65 | 32.26 ± 5.83 | 1.7 ± 0.21 b | |
| Bio-0.010 | 25.06 ± 1.25 b | 9.23 ± 1.02 | 36.79 ± 5.29 | 2.0 ± 0.45 ab | |
| PE-0.010 | 24.30 ± 2.01 b | 9.28 ± 0.11 | 40.38 ± 1.60 | 2.3 ± 0.50 a | |
| Significance | |||||
| Mulching (M) | * | ns | ns | * | |
| Year (Y) | * | ns | ns | ns | |
| M × Y | ns | ns | ns | ns | |
Note: Data presented here are mean ± standard deviation (n = 3, plot means). Different letters within each column indicate significant differences among treatments at p < 0.05 according to one-way ANOVA followed by Tukey’s HSD test. Treatments without letters are not significantly different (ANOVA, p > 0.05). ns, *: non-significant, and significant per p ≤ 0.05 according to two-way ANOVA.
Table 6.
Mechanical properties of the films before use in the 2024 growing season.
| Mulch Type | Thickness | Tensile Load (N) | Tensile Strength (MPa) | Elongation at Break (%) | Tensile Load (N) | Tear Strength (kN/m) | WVTR | |||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| (μm) | MD | TD | MD | TD | MD | TD | MD | TD | MD | TD | (g·m−2·24 h−1) | |
| Bio-0.006 | 6.16 ± 0.52 | 1.85 ± 0.23 | 1.15 ± 0.21 | 19.34 ± 2.19 | 15.08 ± 2.02 | 138.87 ± 68.66 | 443.48 ± 98.42 | 0.7 ± 0.07 | 1.14 ± 0.26 | 106.61 ± 13.54 | 137.23 ± 3.23 | 768.11 ± 13.1 |
| Bio-0.008 | 6.56 ± 0.73 | 2.16 ± 0.08 | 1.72 ± 0.34 | 29.92 ± 3.78 | 18.59 ± 3.35 | 296.36 ± 50.22 | 416.28 ± 46.49 | 0.88 ± 0.11 | 1.22 ± 0.17 | 112.46 ± 12.10 | 185.38 ± 25.75 | 714.47 ± 50.14 |
| Bio-0.010 | 11.58 ± 0.4 3 | 2.24 ± 0.25 | 1.75 ± 0.23 | 25.23 ± 5.31 | 18.25 ± 0.94 | 297.58 ± 25.49 | 473.16 ± 78.22 | 1.24 ± 0.16 | 1.59 ± 0.04 | 133.56 ± 17.41 | 184.61 ± 42.17 | 437.70 ± 16.76 |
| PE | 9.74 ± 0.27 | 2.99 ± 0.81 | 1.77 ± 0.03 | 32.67 ± 1.14 | 25.22 ± 3.43 | 287.88 ± 21.33 | 399.68 ± 12.54 | 1.71 ± 0.62 | 1.39 ± 0.02 | 152.21 ± 10.32 | 183.45 ± 6.11 | 354.15 ± 7.6 |
Notes: All values represent mean ± standard deviation (n = 5 specimens). MD = machine direction; TD = transverse direction. WVTR is the water vapor transmission rate. Because all specimens were obtained from the same film roll, values represent technical replicates rather than independent biological replicates; therefore, no statistical analysis was performed. Data are intended to describe film properties only.
Table 7.
Mechanical properties of the films after use in the 2024 growing season.
| Mulch Type | Thickness | Tensile Load (N) | Tensile Strength (MPa) | Elongation at Break (%) | Tensile Load (N) | Tear Strength (kN/m) | |||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| (μm) | MD | TD | MD | TD | MD | TD | MD | TD | MD | TD | |
| Bio-0.008 | 8.28 ± 0.66 | 1.25 ± 0.47 | 0.84 ± 0.19 | 15.06 ± 5.69 | 15.16 ± 2.57 | 49.18 ± 5.24 | 78.25 ± 7.91 | 0.50 ± 0.23 | 1.10 ± 0.34 | 45.23 ± 8.43 | 71.58 ± 24.49 |
| Bio-0.010 | 10.18 ± 0.24 | 1.89 ± 0.7 | 0.73 ± 0.25 | 18.51 ± 6.83 | 18.51 ± 2.21 | 83.90 ± 7.45 | 92.32 ± 8.49 | 0.71 ± 0.17 | 1.17 ± 0.24 | 51.14 ± 11.21 | 101.45 ± 22.52 |
| PE | 13.08 ± 0.41 | 2.93 ± 1.08 | 1.66 ± 0.09 | 24.16 ± 6.94 | 20.94 ± 1.78 | 251.10 ± 23.51 | 312.31 ± 28.49 | 1.73 ± 0.73 | 1.09 ± 0.22 | 113.31 ± 18.33 | 159.18 ± 17.08 |
Notes: All values represent mean ± standard deviation (n = 5 specimens). MD = machine direction; TD = transverse direction. Mechanical properties of post-use Bio-0.006 could not be measured because the film became excessively brittle and fractured immediately upon stress application. Because all specimens were obtained from the same film roll, values represent technical replicates rather than independent biological replicates; therefore, no statistical analysis was performed. Data are intended to describe film properties only.
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content. |
© 2025 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).
Share and Cite
MDPI and ACS Style
Zhao, H.; Wang, X.; Jin, P.; Zhou, J.; Wang, Y.; Dong, W.; Ren, H.; Li, B.; Gong, W. Effects of Biodegradable Mulch Films with Different Thicknesses on the Quality of Watermelon Under Protected Cultivation. Agronomy 2025, 15, 2336. https://doi.org/10.3390/agronomy15102336
AMA Style
Zhao H, Wang X, Jin P, Zhou J, Wang Y, Dong W, Ren H, Li B, Gong W. Effects of Biodegradable Mulch Films with Different Thicknesses on the Quality of Watermelon Under Protected Cultivation. Agronomy. 2025; 15(10):2336. https://doi.org/10.3390/agronomy15102336
Chicago/Turabian StyleZhao, Haikang, Xidong Wang, Penghui Jin, Jihua Zhou, Yan Wang, Wentao Dong, Huiqing Ren, Bingru Li, and Wenwen Gong. 2025. "Effects of Biodegradable Mulch Films with Different Thicknesses on the Quality of Watermelon Under Protected Cultivation" Agronomy 15, no. 10: 2336. https://doi.org/10.3390/agronomy15102336
APA StyleZhao, H., Wang, X., Jin, P., Zhou, J., Wang, Y., Dong, W., Ren, H., Li, B., & Gong, W. (2025). Effects of Biodegradable Mulch Films with Different Thicknesses on the Quality of Watermelon Under Protected Cultivation. Agronomy, 15(10), 2336. https://doi.org/10.3390/agronomy15102336
Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.
