Dry Direct-Seeded Rice Yield and Water Use Efficiency as Affected by Biodegradable Film Mulching in the Northeastern Region of China

Abstract

In the realm of agriculture, biodegradable films are emerging as a promising substitute for traditional polyethylene (PE) films. Despite their potential, there has been a notable lack of extensive research on their effectiveness in the context of dry direct-seeded rice cultivation. Addressing this gap, a comprehensive biennial study was conducted in the northeastern regions of China, focusing on the ‘Baonong 5’ rice variety. This study meticulously compared three distinct cultivation methods: (1) employing biodegradable film mulching, (2) using conventional plastic film mulching, and (3) cultivating without any mulch. The findings revealed that biodegradable film mulching significantly enhanced soil moisture control, increased leaf area, and improved rice yield and water utilization efficiency (p < 0.05) compared to the plots without mulch. Notably, there was no marked difference in outcomes between the plastic film mulching and the unmulched plots. This research underscores the profound benefits of biodegradable film in rice cultivation, particularly from an environmental sustainability perspective. This innovative method not only boosts agricultural productivity but also addresses critical environmental challenges like climate change and water conservation. The application of biodegradable mulch has proven to be remarkably effective in improving irrigation efficiency and crop water conservation, leading to enhanced rice development and higher yields. The study recorded a substantial increase in water productivity—30% in 2021 and between 52.85% and 60% in 2022—compared to traditional cultivation practices. Furthermore, the use of biodegradable mulch resulted in significantly higher rice yields than the non-mulched plots, thus contributing to increased profitability. Such methods not only yield higher crop outputs but also mitigate environmental issues like water pollution and help alleviate prevalent water shortages in rice farming.

1. Introduction

Mulching with plastic film (PM) has become pivotal in food production, especially in regions with semi-arid climates [1]. The main advantages of PM lie in its ability to retain soil moisture and elevate soil temperature, countering the adverse effects of drought and cold on crop outputs. Nevertheless, the escalating global food demand has intensified the application of plastic films, leading to a rise in plastic remnants in the soil [2]. The subsequent buildup poses risks for soil’s physicochemical makeup and its natural processes [3]. A pressing issue with these plastic remnants is their slow decomposition, which contributes to their prolonged presence in the soil, affecting nutrient distribution and contributing to greenhouse gas emissions [4]. Recognizing these environmental challenges, there has been a shift towards biodegradable films, positioning them as a viable counterpart to conventional plastic films [5]. These eco-friendly films address both food security concerns and sustainable farming initiatives [6]. Transitioning from traditional plastics to these biodegradable options enables farmers to lessen detrimental effects on soil quality while simultaneously curbing the buildup of non-degradable debris [7]. Biodegradable films are designed to break down naturally over time, minimizing their persistence in the soil and reducing the potential for long-term environmental damage [8]. Designed to decompose naturally, biodegradable films limit potential long-term environmental hazards and pave the way for more sustainable farming practices. Such innovations ensure agriculture keeps pace with the needs of a burgeoning population without compromising our ecological balance [9]. In conclusion, the adoption of biodegradable film as an alternative to plastic film in PM technology offers a promising solution to address the negative environmental impacts associated with plastic debris. By prioritizing sustainable agricultural development and considering the long-term health of soil ecosystems, we can strike a balance between food security and environmental stewardship.

While field investigations have indicated analogous yield outcomes between biodegradable mulching (BM) and plastic film mulching (PM), our comprehension of the spatiotemporal dynamics in soil moisture and temperature and their repercussions on crop output remains in its infancy [10,11,12]. Furthermore, the influence of spatiotemporal variations in soil hydration and warmth during the biodegradable film’s decomposition phase on crop yield development is yet to be deciphered. Studies propose that PM can bolster yields in semi-arid locales, primarily by mitigating low-temperature constraints during the germination phase and catering to the hydration needs from panicle initiation to grain filling [13]. Nevertheless, in comparison to PM during the initial growth phase, BM’s efficacy in augmenting temperatures is subdued, and its capacity to retain soil hydration wanes as the film deteriorates [14]. Additionally, later stages of BM have been identified to hasten leaf aging, akin to the effects observed in PM due to temperature accumulation [15]. While certain research papers have delved into the safety implications of biodegradable coverings concerning soil warmth, the focus on its ramifications on soil hydration is scanty [16]. Thus, pinpointing the morpho-physiological processes of crop yield reaction to variances in hydrothermal conditions prior to biodegradable film deterioration is imperative.

Rice, the second largest cereal crop in Northeast China after maize [17], thrives in this region due to its fertile soil, favorable grain structure, and optimal coordination of water, fertilizer, air, and heat [18]. However, the region faces challenges in rice production due to climate change, including rising temperatures, reduced precipitation, and altered precipitation patterns [19]. These factors significantly impact agricultural water availability [20]. In China, rice irrigation alone accounts for a staggering 70% of the total agricultural water usage annually [21]. With the increasing demand for rice and the escalating conflicts arising from the overexploitation of groundwater and limited irrigation water availability, finding rice varieties that require less water and exhibit improved drought resistance has become a critical solution for water conservation in Northeast China [22]. Addressing the water scarcity issue necessitates the development of new rice varieties that can thrive with reduced water requirements [23]. These varieties should also exhibit enhanced resilience to drought conditions. By introducing such varieties, Northeast China can effectively mitigate the strain on water resources while ensuring sustainable rice production [24]. Therefore, the search for water-efficient and drought-tolerant rice varieties holds paramount importance in Northeast China’s quest to address water conservation challenges.

Compared to traditional transplanting and flood irrigation methods, dry-seeded rice cultivation offers water-saving benefits [25]. When combined with mulching, dry-seeded rice can further improve water-use efficiency, address groundwater overexploitation in northern regions, and enhance rice production. Experimental research on fully biodegradable mulch has been conducted on various crops in northern regions, including spring-planted potatoes, peanuts in Northeast China, cotton, cultivar, and maize. These studies have demonstrated the positive effects of biodegradable mulch, such as insulation, moisture retention, promotion of crop growth, increased yield, and reduced plastic residue pollution [26,27]. However, the dry-seeded rice system in northern regions is not well is established, and there a lack of comprehensive research examining the ramifications of biodegradable mulch on biomass proliferation, distribution shifts, and yield fluctuations, whilst alterations in soil hydration have been conducted under conditions specific to dry-seeded rice [28]. This research delves into a representative extended-duration study of rice grown with plastic mulching in the semi-arid sectors of northern China. This study delves into the span of temperature increases in the soil, the oscillations in soil moisture levels, and their subsequent influence on rice output across varied soil temperature scenarios. A central supposition of this study is the potential adverse outcomes on yield induced by temperature variances in the soil, particularly when the degradation timeline of the biodegradable mulch aligns with the critical phase stretching from panicle initiation to grain maturation in rice. To corroborate this hypothesis, the focal points of this investigation are: (i) to dissect alterations in soil’s temperature and hydration attributes across environments characterized by the use of biodegradable mulch, traditional plastic mulch, and no mulching; and (ii) to scrutinize the relationship between water consumption efficiency and rice yields in the context of different mulching scenarios. Through this lens, this research aspires to shed light on the interplay between soil’s heat and hydration dynamics, efficiency of water utilization, and overall yield in dry-seeded rice cultivation.

2. Materials and Methods

2.1. General Situation of the Research Area

The experiment took place at the national modern agriculture industrial park in Jalaid Banner, Inner Mongolia, China (46°41′47″ N, 123°6′52″ E, 170 m a.s.l.). The location of the test site is depicted in Figure 1. It is characterized by a typical middle-temperate continental monsoon climate, with significant temperature fluctuations between day and night. Figure 2 presents the monthly precipitation and average daily temperatures during the rice-growing seasons of 2021 and 2022, highlighting that July 2021 received notably more rainfall than July 2022. This area, primarily cultivating rice and maize as the main crops, is part of the plain agricultural zone. The soil had comparable nutrient content, soil type, and soil physical and chemical properties (

Table 1. The chemical and physical properties of experimental field site of the soil layers (0–20 cm).

Sites	Soil Organic Matter (g kg−1)	Total Nitrogen (g kg−1)	Total Phosphorus (g kg−1)	Total Potassium (g kg−1)	Available Nitrogen (mg kg−1)	Available Phosphorus (mg kg−1)	Available Potassium (mg kg−1)	pH	Clay (%)	Silt (%)	Sand (%)	Field Water Capacity (cm3 cm−3)
Dry fields	24.1	0.11	0.04	2.38	92.8	35.3	130	7.1	13.1	47.6	39.3	0.27

).

2.2. Experimental Protocols and Field Management

Three distinct rice cultivation methods were evaluated: (1) Biodegradable mulching based dryland rice seeding (BM); (2) Direct seeding on dryland with a plastic mulching (PM); (3) Direct seeding of rice without any mulching (NM). The rice variety used in the monoculture was ‘Baonong 5’ (Oryza sativa (italics)). Planting occurred on 21 May and harvesting was performed in late September for 2021 and 2022. For each cultivation method, three plots measuring 9.9 × 10 m² were set up. These plots were isolated using 0.35 mm thick waterproof barriers and buried at a depth of 80 cm to hinder moisture interaction between plots. Throughout the study, weeding was performed manually. Local agronomic practices determined the fertilizer application. The applied rates were: 120 kg of N per hectare (from urea), 50 kg of P₂O₅ per hectare (sourced from calcium superphosphate), and a total of 75 kg of K₂O per hectare (sourced from potassium chloride). Base fertilization involved P₂O₅, 50% N, and 50% K₂O. In this approach, 50% of the nitrogen fertilizer, all of the phosphorus fertilizer, and 50% of the potassium fertilizer were applied as a base fertilizer. The remaining nitrogen fertilizer was then applied in conjunction with irrigation at different growth stages, following the ratio of tillering–flower promoting–flower maintaining = 25%:10%:15%. The remaining potassium fertilizer was applied along with nitrogen fertilizer during the flower promoting stage, also in conjunction with irrigation. Additionally, foliar fertilizer (KHPO₄) was sprayed during the grain filling stage to promote early maturation. Throughout the experiment, field cultivation, pest and disease control, weed management, and fallowing operations were all consistent with local farmers’ management practices.

Within the designated test plot, a specialized process was employed for rice cultivation. Initially, a comprehensive machine was utilized to perform multiple tasks concurrently: planting rice seeds (which were coated), laying black compostable mulch or synthetic sheeting, creating holes, and positioning drip lines. Furthermore, to protect the integrity of the setup, the edges of the mulch were covered with soil, as illustrated in Figure 3. Focusing on the planting details in the arid soil condition, seeds were planted at a depth of 3 cm, with an average distribution of 12 seeds per hole. Providing insight into the materials used, polybutylene adipate terephthalate (PBAT) presented dimensions of 150 cm in width and an 8µm thickness. Impressively, this sheeting conformed to the recent national quality benchmarks (GB/T 35795—2017 [29]). In a similar vein, the synthetic film, spanning 150 cm in width and 10µm in thickness, met the updated national quality guidelines (GB 13735—2017 [30]), as detailed in

Table 2. The suitable standards for different film mulching rice in Northeast China.

Types	Width (cm)	Thickness (mm)	Color	Transmittance (%)	Maximum Tensile Load (N)		Tear Load (N)	Water Vapor Permeability (g (m2 24 h)−1)
					Portrait	Landscape
Biodegradable film	150	≥0.008	Black	<5	≥1.50	≥1.50	≥0.50	<800
Plastic film	150	≥0.010	Black	<5	≥1.60	≥1.60	≥0.80	<800

. To ensure optimal growth conditions, moisture levels were meticulously monitored. For this purpose, a soil moisture sensor (DIK-321A, Daiki Rika Kogyo Co., Ltd., Kounosu, Japan) was strategically positioned in the center of each plot. This setup allowed for the continuous tracking and recording of changes in soil moisture levels, proving invaluable in determining the irrigation schedule.

2.3. Rice Growth Development and Physiological Indices Assessment

Growth Period Assessment: To account for variations in growth periods between water-saving and traditional flood-irrigated rice cultivation, growth stages were meticulously documented. This was based on a combination of morphological observations and field diagnostics, specifically when half of the plants in a plot transitioned into a specific growth phase.

Plant Height, Tillering, and Leaf Area Evaluation: Throughout the rice’s growth cycle, a systematic selection of eight plants per plot was conducted.

Dry Matter and Root Length Analysis: The aboveground portions of rice plants were categorized by organ and prepared for analysis.

Yield and Yield Components: At maturity, eight representative plants were chosen from each plot to count panicles and grains. The yield was measured after drying, with adjustments made for a 14% moisture content.

Quality: Post-harvest, 5 kg of rice was used to determine the rough rice rate according to standard NY/T 83-2017 [31].

Chlorophyll Content: An SPAD-502 m was used to measure chlorophyll content in three leaves from four randomly selected plants per plot. Measurements were taken at different sections of each leaf.

2.4. Field Data Survey and Measurement Soil Temperature

Soil temperature was measured using a soil temperature probe buried in the soil at the time of rice sowing or transplanting, positioned between rows at soil depths of 5 cm, 15 cm, and 25 cm. Data were recorded at 1 h intervals.

Soil Moisture Content: The “soil auger + drying method” was used for measurement. Due to the frequent irrigation during the entire growth period of rice, sampling began 1–2 days before sowing or transplanting and was then conducted approximately every 7 days. Samples were taken from soil depths of 0–60 cm for a total of six times.

Economic Cost Data: Data on the various agricultural input costs, land leasing, and labor expenses in different rice-planting models in Northeast China were sourced from field surveys.

2.5. Statistical Evaluations

In the data processing phase, Excel 2020 was employed for data organization and computation, focusing on the raw data obtained from our field experiments. For rigorous statistical analysis, we utilized SPSS 20.0 (IBM Corp., Armonk, NY, USA). To rigorously assess significant variations across different treatment groups, we applied a one-way analysis of variance (ANOVA) and further elucidated differences in means through post hoc analysis using the Least Significant Difference (LSD) test. A significance level of p < 0.05 was rigorously adhered to in order to ascertain statistical significance. Furthermore, to visually represent our findings, graphical visualizations were meticulously crafted using Origin 2021b (OriginLab, Northampton, MA, USA).

3. Results

3.1. Effects of Varied Covering Substances on Soil Humidity and Temperature

3.1.1. Soil Temperature

In our field study, we observed the fluctuations in the daily mean soil temperature for each treatment during 2021 and 2022, as illustrated in Figure 4. During the rice’s entire growth phase, temperature variations at varying soil depths exhibited a consistent pattern in 2021. For soil depths of 5 cm, 15 cm, and 25 cm, when treated with the BM and PM approaches, the daily temperature increments were 0.4% and 4.3%, 0.2% and 3.9%, and 0.0% and 3.1% in relation to the NM method, respectively. Notably, as we delved deeper into the soil profile, this warming influence started to diminish. The thermal impact of the film in 2022 was on par with 2021. However, the amplified warming was a consequence of reduced rainfall in 2022. For the depths of 5 cm, 15 cm, and 25 cm in 2022, the BM and PM treatments led to temperature hikes of 1.1% and 4.9%, 0.7% and 3.6%, and 0.1% and 3.3%, respectively, when juxtaposed with the NM approach. Furthermore, a noteworthy observation was that cooler temperatures enhanced the warming potential of the film. It was also evident that rice under the biodegradable film experienced a sharp rise in temperature during its initial growth stages (p < 0.05), but this effect diminished or vanished altogether as the mulching film degraded and as the rice progressed in its growth cycle.

3.1.2. Soil Moisture

In the field test, variations in soil moisture for a depth of 0–20 cm across different treatments during 2021 and 2022 are depicted in Figure 5. Influenced by the experimental setup, precipitation patterns, and other factors affecting water intake and usage, the moisture levels within the 0–20 cm depth for the BM treatment appeared consistent with those observed for PM and NM treatments, staying within a specified range of from 11.8% to 26.6%. Furthermore, when considering the effects of various materials, it was noted that the soil’s water content in the PM treatment persisted longer than in alternative treatments.

3.2. The Impacts of Different Covering Materials on Rice Growth and Photosynthetic Characteristics

3.2.1. Rice Growth

As outlined in Figure 6, notable variations were observed in the growth stages of rice subjected to different treatments. For the years 2021 and 2022, rice under the BM treatment sprouted 7–8 days earlier than the NM-treated rice. The NM treatment had its panicle initiation stage advance by about 5 days, the anthesis stage by roughly 3 days, and the MF stage by an approximate 3 days. When considering the total growing duration, rice exposed to the BM and NM treatments grew for 146–152 days. However, the BM-treated rice had a growth phase extending 7 days more than its NM counterpart. Notably, an absence of marked disparities existed in the rice growth durations between BM and PM. Owing to the variances in emergence times, there were noticeable year-to-year differences in growth durations for 2021 and 2022.

In the biennial field study, we observed uniform growth height patterns in rice. This study details critical phenological stages, including mid-tillering (MDT)—when secondary shoots start developing; max-tillering (MT)—the stage with the highest number of shoots; panicle initiation (PI)—the beginning of flowering head development; anthesis (AN)—the flowering period; milk filling (MF)—when grains are filling with milky fluid; and grain maturity (GM)—when grains are fully matured. During the MF phase, as illustrated in Figure 7, the length of these phenological periods was evident. Compared to the NM treatment, rice treated with BM and PM demonstrated significantly increased heights, with increments of 14.7% and 12.0% during the MDT phase, 21.8% and 19.3% during the MT phase, 13.2% and 13.7% during the MF phase, and 7.2% and 7.9% during the GM phase, respectively. However, the height differences between the BM and PM treatments were marginal.

During the field experiments in 2021 and 2022, the shoot dry matter and root dry matter of each treatment showed almost the same trend, increasing with the development of the growth stage and reaching a maximum at the GM stage. The dry weight of the shoot and root were significantly higher than those of the non-mulching treatment (p < 0.05), but there was no significant difference between the BM and PM treatments. Under the BM and PM treatments, the number of tillers and the leaf area index consistently surpassed those observed with the NM treatment in Figure 8. Notably, at the mid-tillering (MDT) stage, the BM and PM treatments exhibited increases in tiller count of 32.6% and 32.4%, respectively, while leaf area expanded by 34.2% and 28.1%. Progressing to the max-tillering (MT) stage, there was a further elevation in tiller numbers of 26.1% and 25.8%, and in leaf area of 29.1% and 26.8% under BM and PM treatments, respectively. During the panicle initiation (PI) phase, the increase in tillering was recorded at 18.9% and 20.8%, and leaf area at 21.9% and 21.4%. In the anthesis (AN) stage, both BM and PM treatments demonstrated a 14.5% rise in tillering, accompanied by leaf area growths of 21.0% and 22.5%. At the milk filling (MF) stage, tiller numbers were augmented by 6.8% and 4.2%, and leaf area by 17.2% and 18.6%. Finally, during the grain maturity (GM) stage, there was an uptick in tillering of 6.6% and 5.2%, and in leaf area of 10.4% and 12.0%. It is important to note, however, that the differences in tiller numbers and leaf area index between the BM and PM treatments were not statistically significant.

Variations in shoot dry mass and 0–40 cm deep root dry mass throughout the rice’s growth phase, under diverse planting techniques, are depicted in Figure 9 and Figure 10. In the 2021 and 2022 field studies, the shoot and root dry mass for each cultivation method exhibited a consistent pattern, escalating as the growth phase progressed and peaking during the GM phase. Compared to the non-mulching regime, the dry mass of the shoot and root was markedly elevated (p < 0.05). However, distinctions between the BM and PM methods were negligible. Compared to the non-mulching treatment (NM), rice treated with BM and PM during the growth period exhibited significant increases in shoot dry matter and root dry matter at different growth stages. During the max-tillering stage (MT), the shoot dry matter in the BM and PM treatments increased by 20.8% and 24.4%, respectively, while the root dry matter increased by 14.3% and 17.2%. At the panicle initiation stage (PI), the increases in shoot dry matter for BM and PM treatments further reached 32.6% and 34.9%, respectively, with corresponding increases in root dry matter of 17.2% and 18.8%. During the anthesis stage (AN), these treatments resulted in shoot dry matter increases of 31.7% and 35.0%, and root dry matter increases of 19.8% and 22.0%. In the final phase, the grain maturity stage (GM), the treatments with BM and PM resulted in notable increases in shoot dry matter, with rises of 21.1% and 22.8%, respectively, and in root dry matter, with increases of 12.7% and 14.8% correspondingly.

3.2.2. Rice Photosynthetic Characteristics

Figure 10 illustrates the variations in SPAD value, photosynthesis (Pn), transpiration rate (Tr), and stomatal conductance (Gs) for rice across distinct growth phases in Northeast China under varied cultivation techniques. Throughout the growth cycle of rice, the photosynthetic traits for every method exhibited a pattern reminiscent of an inverted “V”. The SPAD measurement for rice ascended quickly from the MT phase to the PI phase, moderated its rise from the PI phase to the AN phase, and then underwent a decline from the AN phase to the MF phase. The values for Pn, Tr, and Gs in rice surged from the MT phase to the AN phase and then diminished swiftly from the AN to the MF phase. Notably, the disparity in photosynthetic attributes between the BM and PM methods was not pronounced. However, when juxtaposed with the NM method, the BM and PM methods showed notable variations in photosynthetic traits (p < 0.05). Furthermore, the Tr for both BM and PM methods consistently remained below the levels observed in the NM method throughout all phases, and the remaining photosynthetic metrics surpassed those of the NM method.

3.3. Effects of Diverse Cover Materials on Water Intake and Productivity

Water intake displayed variations across the different treatments. During the growth span of mulching for dry direct-seeded rice (both BM and PM methods), the rainfall patterns deviated from the NM approach (refer to

Table 3. Assessment of water consumption and water efficiency in rice cultivation methods during 2021 and 2022. BM entails rice sowing in dry soil conditions utilizing eco-friendly film coverings, whereas PM involves rice sowing on arid lands using synthetic film covers. On the other hand, NM stands for the rice seeding process on dry terrains without the use of any mulch. The data presented are averaged and are accompanied by a standard deviation value (n = 3). Variations in alphabetic labels in columns point to distinct differences, with a statistical significance observed at p < 0.05 (based on the LSD test).

Year	Treatment	Rainfall (mm)	Irrigation (mm)	Total Water Input (mm)	Irrigation Water Productivity (kg m−3)	Total Water Productivity (kg m−3)
2021	BM	451	164 ± 14 a	615 ± 14 a	4.77 ± 0.23 a	1.27 ± 0.05 a
	PM	451	146 ± 20 a	597 ± 20 a	5.21 ± 0.27 a	1.28 ± 0.05 a
	NM	451	225 ± 20 b	676 ± 20 b	2.90 ± 0.15 b	0.97 ± 0.06 b
2022	BM	327	305 ± 27 a	632 ± 27 a	2.55 ± 0.14 b	1.23 ± 0.07 a
	PM	327	278 ± 23 a	605 ± 23 a	2.81 ± 0.12 a	1.29 ± 0.06 a
	NM	327	451 ± 31 b	778 ± 31 b	1.41 ± 0.09 c	0.82 ± 0.08 b

). Concurrently, distinctions in irrigation water intake were evident, where the NM approach registered the highest intake (with a mean value of approximately 238 mm). Despite the BM and PM methods not showing marked differences in their water intake (averaging 235 mm and 212 mm, respectively), their respective water consumptions saw a decline by about 30.6% and 37.3% when set against the NM method. Notably, variations in total water intake manifested across the two study seasons, and the intake was higher in 2022 (BM: 632 mm; PM: 605 mm) compared to 2021 (BM: 615 mm; PM: 597 mm).

Water productivity denotes the yield ratio to water consumption volume. Discrepancies were observed in irrigation water productivity over the two studied years, with the NM method exhibiting the least efficiency (as per Table 3). When benchmarked against the NM method, both BM and PM displayed enhancements in their irrigation water productivity, recording increments of 0.6 and 0.8 times in 2021 and of approximately 1.0 times in 2022. On average, the 2021 irrigation water productivity across all methods surpassed the 2022 values by roughly 90.3% (p < 0.05). Moreover, the overall water productivity trends for the three methods largely mirrored their irrigation productivity trends, but no marked differences were noted for the BM and PM methods in 2022. Relative to the NM method, total productivity rates were elevated in 2022 for the BM and PM methods, showing increments of 0.9 and 0.6 times, respectively.

3.4. The Effects of Diverse Covering Materials on Rice Production and Overall Profitability

No pronounced variations in grain yields were observed between the BM and PM treatments over the studied years. However, the grain yields for both these treatments outperformed the NM treatment (Refer to Figure 11). Analyzing the number of two-year panicles, BM stood out as the superior treatment, closely followed by PM, leaving NM with the least. Interestingly, while the spikelets per panicle in BM and PM remained consistent over the years, they were noticeably fewer than in NM (p < 0.05) for 2021. In the subsequent year, BM and PM displayed a dip ranging from 5.3% to 6.4% in terms of filled grains when juxtaposed with NM. Throughout the duration of the study, NM showcased a notably higher grain weight per 1000 grains than PM. Yet, NM’s weight differences remained statistically indistinguishable from BM. Further evaluations indicated an absence of discernible disparities in quality parameters such as amylose content and chalkiness (Figure 12).

Contrasting with the NM, both BM and PM incurred elevated expenses primarily due to their reliance on agricultural coverings, as detailed in

Table 4. In 2021 and 2022, the input–output for rice production followed specific patterns: BM represents rice produced through direct dryland seeding using biodegradable film mulching; PM denotes rice produced using direct dryland seeding with plastic film mulching; and NM refers to rice produced using direct dryland seeding without any mulching.

Classification	Subclass	BM	PM	NM
Agricultural materials input (CNY ha−1)	Seeds	1125	1125	1125
	Seedling	0	0	0
	Drip tape and water pipe	1050	1050	1050
	Film	2150	1575	0
	Fertilizer	2025	2025	2025
	Pesticide	525	525	1050
	Irrigation water and electricity	1050	1050	1500
Leasehold and labour (CNY ha−1)	Leasehold	7500	7500	7500
	Soil preparation	525	525	525
	Sow or transplant	300	300	300
	Supplement seeding	150	150	150
	Labor control	1050	1050	1500
	Harvest	825	825	825
	Plastic film recycling	0	600	0
Total cost (CNY ha−1)		18,275	18,300	17,550
Yield (kg ha−1)		7802	7719	6453
Rice price (RMB kg −1)		3.5	3.5	3.5
Net profit (CNY ha−1)		9032	8718	5035

. The expenditure patterns revealed that the bulk of the cost difference came from purchasing and recycling plastic films. Positively, these covering materials led to a tangible decline in expenses associated with pest management and curbing weed growth. When reviewing the economic impact, investment returns from different rice production methods varied between CNY 17,550 and 18,300 ha⁻¹ in 2021 and 2022. Taking yield and market price into account, profits for NM dwindled by CNY 3997 ha⁻¹ relative to BM but saw a more substantial reduction of CNY 3683 ha⁻¹ when compared with PM.

4. Discussion and Conclusions

4.1. Soil Condition

Mulching in rice cultivation plays a pivotal role as a method for conserving water. It indirectly impacts the physiological development and output of rice by modulating soil temperature, enhancing soil properties, and preserving its moisture levels. In a recent study, the soil warming effect of various mulching water-saving planting patterns gradually weakened or disappeared with increasing soil depth [32]. This could be attributed to the fact that mulching isolates the soil from external water exchange, leading to an increase in soil heat flux and temperature by reducing heat exchange between the soil and the outside world, specifically latent heat loss [33]. Additionally, mulch acts as a barrier, preventing the exchange of matter and energy between the paddy field and the external environment [34]. This allows for water vapor evaporated from the soil to be retained in the air chamber between the paddy field and the mulch, thereby slowing down the rate of evaporation [35]. During the reproductive period, different mulching techniques, such as biodegradable mulch cover and ordinary mulch cover in dry cropping planting patterns, exhibited varying warming effects on paddy soil. All mulch cover treatments showed higher temperatures than the non-mulch treatment from 0 to 70 days, with differences among the three treatments becoming less apparent after 70 days. Similar results have been observed in previous studies. Several factors contribute to this phenomenon [36]. Firstly, biodegradable mulch starts degrading and covering the soil surface at a later stage of plant growth [37]. Throughout the cultivation cycle, the soil temperature dynamics influenced by diverse mulching techniques are intricately tied to the early growth stages’ limited plant canopy. Initially, this smaller canopy size facilitates significant sunlight penetration into the soil under the mulch. As the plants develop, the disintegration of biodegradable mulch exposes more soil. This exposure renders the soil prone to alkaline salt leaching from rainwater, leading to a marked reduction in soil pH [38]. Concurrently, as the vegetation matures, its foliage provides considerable shade to the mulched soil, effectively reducing sunlight exposure, thereby moderating soil temperatures. Additionally, elevated soil temperatures catalyze microbial metabolic processes, hastening the breakdown of organic matter within the soil. This nuanced understanding of the soil–environment interplay under different mulching regimes is essential for optimizing cultivation practices.

4.2. Crop Growth

It has been observed that both biodegradable mulch film treatment and ordinary mulch film treatment, when compared to non-coating treatment, contribute to an accelerated growth period of rice, particularly in the early stages. The total growth period of rice was shortened by approximately 7 days with the use of these mulch film treatments. This can be attributed to the fact that mulching increases soil temperature and moisture, thereby enhancing the growth rate of rice. Additionally, mulching improves soil permeability and promotes the development of rice roots, which are vital for nutrient and water absorption, as well as the synthesis of various physiologically active substances associated with the root system [37,39]. Notably, these influences are predominant during the early growth phases of rice when coated mulch films are used. As rice matures during its intermediary and concluding phases, the soil-warming and moisture-retaining benefits of mulching wane and ultimately vanish. Consequently, the content of soil moisture becomes a paramount factor determining rice growth in the varied mulch-based plantation method [40]. Insufficient soil moisture, caused by mulching, leads to increased ineffective tillering in the later growth stage. The formation of rice yield relies on the continuous accumulation of dry matter, as supported by research findings [41]. In scenarios of efficient water management, a limited water supply results in lower aboveground biomass, thereby influencing overall crop productivity.

These observations have highlighted that the adoption of biodegradable mulch film treatment, in conjunction with plastic mulch film treatment, led to a notable reduction in transpiration when set against traditional dry-farming methods. Concurrently, the aboveground metrics, encompassing both plant height and dry weight, presented an upward trend throughout the growth phase. This observation corroborates findings from recent studies focusing on the implications of water-efficient planting strategies for rice, underlining that a reduced transpiration rate is offset by an expansion in the leaf area [42]. The growth and development of rice roots are influenced by various factors, including planting methods, farmland environment, and rice varieties. Over a span of two years, an interesting trend was observed: initially, there was a rise in the total root length across all treatments. However, as the plants matured, especially during the formative growth phases, rice cultivated under both the biodegradable mulch and the regular mulch showed a notable increase in root dry weight and overall root length when juxtaposed with rice grown under traditional dry-farming methods. Yet, this difference became less pronounced in the latter growth stages. As rice enters the flowering period, the warming effect of the mulch gradually diminishes, leading to the gradual aging of vegetative organs and a subsequent decrease in root length and dry weight. More than 90% of the total root length of the treated rice was concentrated in the uppermost 20 cm of the soil, with a decreasing length as the soil depth increased. Notably, the mulch film-covering treatment and biodegradable mulch film-covering treatment demonstrated a greater total root length in deep soil [43].

4.3. Water Use Efficiency

Studies have revealed that when set against the untreated control, both biodegradable mulch film and traditional mulch film treatments accelerated the maturation cycle of rice. This acceleration was most pronounced during the initial growth phase of rice. Overall, the growth span for rice under the influence of both biodegradable and conventional mulch treatments saw a reduction. This reduction in the growth period can be attributed to an approximate 7-day difference. One probable reason for this observation is the role of mulching in modulating soil temperature and preserving soil hydration, thus fostering a more conducive environment for rice growth [44]. Moreover, mulching enhances soil receptiveness, aiding in the proliferation of rice roots. These roots, vital to the overall crop health, play a dual role: they are the primary channels for water and nutrient uptake and they also engage in the production of several compounds crucial for plant physiology. Such enhancements in root functionality and environment may be responsible for the expedited growth cycle observed in mulch-treated rice.

In the intermediate-to-advanced growth phases, the temperature-raising and water-holding abilities of mulching slowly waned. As a result, soil moisture turned into the principal growth constraint for rice in different mulching setups. When employing mulch, the soil’s moisture content positively influenced the ineffective tillering in the growth’s maturation phase, and rice production was reliant on the persistent buildup of dry substances, a notion backed by prior studies [41,45]. Under water-efficient rice-planting conditions (excluding extreme drought and water conservation), the reduction in aboveground dry matter tends to be less than that of the crop [46]. As a result, its moisture productivity is increased [47]. It was found that the transpiration of dry-fed and ordinary mulch was reduced compared with uncovered dry-farming, but the aboveground accumulation (dry weight and plant height) increased throughout the growth period [48]. The growth and development of rice roots is affected by factors such as planting mode, farmland environment, and rice varieties [49]. Observations showcased a consistent uptrend over two years in the root dry mass across various treatments, although the root length demonstrated an initial expansion followed by a contraction [50]. Post-flowering, the temperature moderation provided by the mulch diminishes, leading to a decline in root span and mass. On average, a significant portion, around 90% of the treated rice root length, was localized within the top 20 cm of the soil stratum. The depth of rice rooting and enhanced nutrient absorption are often influenced by the type of mulch application. Preliminary results suggest a notable augmentation in irrigation efficiency and crop water conservation when utilizing both conventional and biodegradable mulching. By adopting these water-conserving strategies, particularly with biodegradable and conventional mulch applications, there was a pronounced improvement in rice development and crop yield in the aforementioned region. When contrasted with non-mulched fields, the utilization of these mulch types led to a boost in water productivity of 30% in 2021 and of between 52.85% and 60% in 2022.

4.4. Economic Benefits

Previous research findings have demonstrated that both biodegradable mulch film and conventional mulch film can effectively enhance the yield of various crops, including potatoes, melon, and spring maize [51,52]. Similarly, the present study confirms that the average yield of dry-seeded rice is significantly higher when grown under mulch film compared to non-mulch film conditions. The utilization of biodegradable mulch film plays a crucial role in reducing water evaporation, optimizing water utilization efficiency and maintaining appropriate soil temperature and moisture levels during the critical growth phases of the crops [37]. This technique contributes to an increased leaf area index, stimulates root development, and improves the overall net photosynthetic efficiency of the rice plants, indirectly influencing their physiological growth and subsequent yield. The application of biodegradable mulch film resulted in an increase in spikelet number, grain weight per spikelet, and 1000-grain weight in dry-seeded rice. Despite the decrease in spikelet number caused by using biodegradable mulch film, the compensatory increase in grain weight per spikelet and 1000-grain weight balanced out the reduction in spikelet number. It is noteworthy that the experimental site experienced relatively high precipitation during the 2021 and 2022 growing seasons, with the peak water demand period coinciding with the reproductive rice of phase. Adopting biodegradable mulch film for dry-seeded rice cultivation not only stabilizes yields but also presents a promising new approach to water-saving rice production.

Economic benefits and planting inputs are the main factors that farmers consider when choosing crop cultivation methods [53,54,55]. Studies suggest that employing either biodegradable or traditional mulch film can elevate rice farming expenses but also enhance overall earnings. The additional costs associated with biodegradable mulch film primarily stem from its purchase, but it reduces the need for pest control and weed management, leading to lower pesticide costs. Moreover, biodegradable mulch film significantly enhances rice yields, resulting in increased net profits and a higher benefit–cost ratio. However, challenges arise from rural labor shortages, seasonal droughts, and groundwater scarcity when maintaining the same planting methods for rice transplanting. Nevertheless, there is tremendous potential for mechanization and technological advancements in rice cultivation, especially in dry-seeded conditions under mulch film. Therefore, integrating dry-seeded rice cultivation with biodegradable mulch film holds considerable promise as an agricultural management system. It can enhance rice yields, improve water utilization efficiency, sustainably increase farmers’ income, and ensure food security in Northeast China.