Impact of Management Strategies on Reducing of Mulching Film Residues Pollution in Arid Regions

Abstract

Plastic pollution caused by mulching film residues (MFRs) is escalating in arable lands, which affects the function of agricultural ecosystems, and poses a serious obstacle to agricultural sustainable development in arid regions. Internationally, increasing recycling rate of polyethylene (PE) film and adopting biodegradable films are recommended strategies to mitigate plastic pollution in farmland, aiming to increase agricultural sustainability and food security. However, impacts of the future of these strategies remain underexplored. This study estimated MFRs accumulation over the next 50 years under varying PE and polybutylene adipate terephthalate (PBAT) film recovery scenarios: no recovery, and recovery rates increased to 80%, 85%, 90%, and 95%. Additionally, cumulative ecological effects (CEEs) of MFR pollution were assessed based on historical MFRs accumulations of 75 kg hm⁻², 160 kg hm⁻², 220 kg hm⁻², 300 kg hm⁻², and 400 kg hm⁻², by evaluating direct and indirect ecological effects. The findings revealed that (1) with no recovery, PE film residues could increase by 480 kg hm⁻², whereas achieving a 95% recovery rate could limit residues increasing to below the national threshold of 75 kg hm⁻², outperforming the 80%, 85%, and 90% recovery rates. On the other hand, using PBAT film would maintain the increasing MFRs below 75 kg hm⁻² regardless of recovery rate. (2) Without PE film recovery, CEEs would intensify significantly, as both the direct and indirect effects increase notably, while the CEEs of MFRs could maintain the current status or decrease under the strategy of 95% recovery rate of PE film and using PBAT film, similar to the variation of direct effects. However, indirect effects would persist due to ongoing microplastics (MPs) and phthalate esters (PAEs) released from residual films. Overall, a 95% PE film recycling rate and PBAT film usage emerged as particularly effective strategies for minimizing MFRs accumulation and mitigating ecological impacts over the next 50 years. Further research should prioritize the indirect ecological effects of MFRs, given their persistence despite reduction efforts. The results could provide a theoretical support for agricultural sustainable development in arid regions.

1. Introduction

Mulching film is an essential material in modern agriculture, providing benefits such as weed suppression, reduced water evaporation, enhanced plant growth, and increased crop yields [1,2]. This practice is especially prevalent in both arid and humid regions [1,3]. However, poor recycling rates over the past decades have led to an accumulation of plastic debris in soils [4,5,6]. The rising plastic pollution from mulching film residues (MFRs) in farmland has become a major barrier to sustainable agricultural development [7,8,9].

Many studies have quantified MFRs levels in soils and identified factors influencing their accumulation across humid to arid regions. These studies indicate that MFRs concentrations are significantly higher in arid regions, typically accumulating in the topsoil layer (0–30 cm), with average levels ranging from 136.7 to 259.1 kg hm⁻² [6,10,11]. In some areas, the residues have reached up to 502.2 kg hm⁻² [12]. As an essential material for crop production in arid areas, mulch would continue to be used; however, research on variation of MFRs accumulation in the future is limited domestically and internationally [13,14].

MFR pollution poses direct and indirect threats to agricultural ecosystems, presenting a long-term environmental challenge [7,9]. Directly, residual plastics lead to continuous soil degradation, causing damage to soil structure, altering soil bulk density, reducing soil porosity, and disrupting the vertical penetration and horizontal transport of soil water [8,15,16,17]. These effects negatively impact seed emergence, root growth, biomass accumulation, and crop yields [8,18,19]. Indirectly, MFRs release microplastics (MPs, ≤5 mm in size) and plastic additives during degradation, causing a series of hazards [20,21,22]. MPs can reduce water and nutrient uptake by blockage of pores in seed coat or roots, inhibiting plant growth [22,23]. Moreover, MPs can be absorbed and transported to other plant organs by transpiration, and can accumulate in higher animal bodies through the food chain, potentially harmful to human health [22,24,25,26]. Phthalic acid esters (PAEs), as the main ingredient in plastic additives, also pose threats to crops, microbes in soil, animals, and humans [27,28].

Assessing the long-term ecological impacts of MFRs on agricultural ecosystems is essential, and comprehensive studies on the overall impacts of MFRs remain sparse [7,18,19]. This gap underscores the limited understanding of MFR pollution as an environmental issue [7,13]. To mitigate MFR pollution, the Food and Agriculture Organization (FAO) has proposed global strategies for improving agricultural plastic management [29]. In China, government initiatives aim to address this issue by targeting a recovery rate of over 80% for polyethylene (PE) films and encouraging using biodegradable films [30], and polybutylene adipate terephthalate (PBAT) film is a relatively common biodegradable film in the market [31,32]. However, further research is needed to assess the effectiveness of these measures [3,7,33,34].

This study estimates the accumulation of MFRs over the next 50 years under strategies involving increased PE film recovery and the use of PBAT film. Additionally, it evaluates the cumulative ecological effects (CEEs) of MFR pollution under different historical accumulation levels to assess the impact of these strategies [9]. This research aims to offer valuable insights into the prevention and relief of residual film pollution in agricultural ecosystems, promoting agricultural sustainable development.

2. Materials and Methods

2.1. Scenarios

Investigations demonstrated that MFRs in most fields were greater than the national film residue standard (75 kg hm⁻²), and even up to 502.2 kg hm⁻², increasing with increasing mulching years [10,11,12]. Accumulations of 75 kg hm⁻², 160 kg hm⁻², 220 kg hm⁻², 300 kg hm⁻², and 400 kg hm⁻² were chosen as the typical historical accumulation in different mulching years fields [10,11,12]. In order to better understand the variation of accumulation of MFRs over the next 50 years in those fields under different management strategies, this study established ten strategic scenarios (

Table 1. Strategies and historical conditions.

Strategies for Mitigating MFR Pollution						Historical Conditions
Strategies	Film Type	Film Usage (kg hm−2)	Thickness (TK) (mm)	Recycling Rate	Value of Fr
PE-S0	PE film	60–80	0.010	0	50.7%	HC1: 75 kg m−2 accumulated historically HC2: 160 kg m−2 accumulated historically HC3: 220 kg m−2 accumulated historically HC4: 300 kg m−2 accumulated historically HC5: 400 kg m−2 accumulated historically
PE-S1	PE film	60–80	0.010	80%	20%
PE-S2	PE film	60–80	0.010	85%	15%
PE-S3	PE film	60–80	0.010	90%	10%
PE-S4	PE film	60–80	0.010	95%	5%
PBAT-S0	PBAT film	60–80	0.010	0	50.7%
PBAT-S1	PBAT film	60–80	0.010	80%	20%
PBAT-S2	PBAT film	60–80	0.010	85%	15%
PBAT-S3	PBAT film	60–80	0.010	90%	10%
PBAT-S4	PBAT film	60–80	0.010	95%	5%

Note: 50.7% refers to “Manual for Mulching Film Residue Coefficient” [35].

).

2.2. Estimation of Accumulation of Mulching Film Residues

The conceptual model for residual film accumulation is presented as Equation (1):

$$Q={\displaystyle \sum _{i=1}^n(F_{mi}\times F_{ri})}$$

(1)

where Q represents the amount of MFRs, kg hm⁻². The variable n is the years of using mulching film. F_mi is the amount of film used in the ith year, kg hm⁻². F_ri is the residual rate of mulching film in the ith year, % (Table 1).

The increasing amount of residual film (ΔQ) and the cumulative amount of residual film (Q) in the future based on historical accumulations were calculated as Equations (2) and (3):

$$\Delta Q={\displaystyle \sum _{i=1}^n{F}_{mij}{F}_{rij}{(1-d_j)}^{n-1}}$$

(2)

$$Q=Q_0+\Delta Q$$

(3)

where F_mij is the amount of jth film usage in the ith year, kg hm⁻². F_rij is the residual rate of jth film in the ith year, % (Table 1). d_j is the degradation rate of jth film, where the values of PE film and PBAT film are 2.8% and 45.9%, respectively [36,37]. Q₀ is the historical accumulation of MFRs, kg hm⁻².

2.3. Evaluation of Cumulative Ecological Effects of Mulching Film Residues

2.3.1. Evaluation of Cumulative Ecological Effects

Under impact of management strategies, the cumulative amount and type of MFRs in soil are constantly changing [3]. Furthermore, the MPs and additives released from MFRs would continue to accumulate with the tillage, aging, and degradation of MFRs in future [7,33]. As a result, the effects of MFRs, MPs, and additives on agro-ecosystems and organisms continue to change, which is in line with the concept of cumulative ecological effects [7,9,18,38]. This paper draws on the concept of cumulative ecological effects (CEEs) to analyze the variation of ecological effects of MFRs in the future, in order to better understand the impacts of management strategies on mitigating MFR pollution [7,9,13].

To evaluate CEEs of MFRs, an index system was developed based on the direct and indirect ecological effects of MFRs (

Table 2. Index system for evaluating cumulative ecological effects of mulching film residues.

Benchmark Layer	Index Layer	Meaning
Direct ecological effects index (Ide)	Rate of water evaporation reduction	Impacts of MFRs on soil physicochemical properties
	Rate of water infiltration reduction
	Rate of organic matter reduction
	Rate of available phosphorus reduction
	Rate of crop yield reduction	Obstruction to crop production
Indirect ecological effects index (Iie)	Accumulation of microplastics from film	Potential risk from MPs
	Accumulation of plastic additives from film	Potential risk from additives

) [7]. The direct effects of MFRs on farmland ecosystems were assessed by examining their influence on crop yield and soil physicochemical properties, such as changes in water evaporation, water infiltration, organic matter content, and available phosphorus content in soil [8,18,19]. The indirect effects primarily considered pollution from microplastics (MPs, ≤5 mm in size) and phthalate esters (PAEs) [15,16,17,38,39,40]. Plastic additives, including plasticizers, antioxidants, heat stabilizers, lubricants, and colorants, are components of plastic pollution [26]. In this study, the accumulation of PAEs from MFRs was utilized to analyze the risk associated with plastic additives, with PAEs being studied systematically [26,41,42].

The cumulative ecological effects index (I_ce) were used to represent the CEEs of MFRs, as modeled by Equation (4) below:

I_ce = I_de+ I_ie

(4)

When I_ce values range from 0 to 0.75, CEEs is considered low; values from 0.76 to 1.50 indicate a medium level, and values from 1.51 to 2.00 suggest high-level CEEs from MFR pollution [43].

2.3.2. Evaluation of Direct Ecological Effects of Mulching Film Residues

The direct ecological effects (I_de) of MFRs on farmland ecosystems was evaluated by Equations (5)–(7):

$$I_{de}={\displaystyle \frac{{CI}_{de 0}-{CI}_{de}{}_{min}}{{CI}_{de}{}_{max}-{CI}_{de}{}_{min}}}$$

(5)

$${CI}_{de}=\sqrt[5]{{CI}_{1j}\times {CI}_{2j}\times {CI}_{3j}\times {CI}_{4j}\times {CI}_{5j}}$$

(6)

$${CI}_{ij}={\mathsf{\Delta }d}_i\times {\displaystyle \raisebox{1ex}{$Q_j$}\!\left/ \!\raisebox{-1ex}{$100$}\right.}$$

(7)

where CI_ij is the value of the ith item in jth years, and i is from 1 to 5, covering factors such as water evaporation, water infiltration, organic matter content, available phosphorus content, and crop yield. Q_j represents the accumulation of MFRs in the jth year; Δd_i is the value of change in the ith item with an increase of 100 kg hm⁻² of MFRs, and the Δd of water evaporation, water infiltration, organic matter content, effective phosphorus content, and crop yield are −2%, −8%, −0.8%, −5%, and −3%, respectively [18]. I_de values are standardized from the original data to a range of 0 to 1.0 using the min–max method, where the minimum value is set to 0.

2.3.3. Evaluation of Indirect Ecological Effects of Mulching Film Residues

The indirect ecological effects (I_ie) were evaluated using Equations (8)–(10):

$$I_{ie}=\sqrt[2]{I_{ie}{}_1\times I_{ie}{}_2}$$

(8)

$${CF}_i=\raisebox{1ex}{$C_i$}\!\left/ \!\raisebox{-1ex}{$C_{oi}$}\right.$$

(9)

$$I_{ie}{}_i={\displaystyle \frac{{CF}_i{}_0-{CF}_i{}_{min}}{{CF}_i{}_{max}-{CF}_{imin}}}$$

(10)

where CF_i is the pollution coefficient of the ith pollutant item, referring to MPs and PAEs. C_i is the accumulated amount of MPs or PAEs, mg kg⁻¹. C_0i is the safe concentration threshold of MPs and PAEs below which there is no impact on organisms. The safety concentration of MPs is less than 1000 mg kg⁻¹, which is safe for soil organisms such as earthworms [39,44]. The limit of PAEs is 5 mg kg⁻¹, according to the United States soil cleanup standards (1994) [45].

(1)

The cumulative amount of MPs was calculated as Equations (11)–(13):

$$Q_{mps}=Q_{0 mps}+Q_i{}_{ mps}$$

(11)

$$Q_0{}_{mps}={\displaystyle \raisebox{1ex}{$Q_0\times {EF}_0$}\!\left/ \!\raisebox{-1ex}{$D\times \rho \times {10}^3$}\right.}$$

(12)

$$Q_{i mps}={\displaystyle \sum _{i=1}^n\raisebox{1ex}{$Q_{mi}\times {EF}_j$}\!\left/ \!\raisebox{-1ex}{$D\times \rho \times {10}^3$}\right.}$$

(13)

where Q_mps is the accumulation amount of MPs in the soil, mg kg⁻¹. Q_{0 mps} is the historical accumulation of MPs. Q_{i mps} is the increasing amount of MPs in the ith year, mg kg⁻¹. Q_mi is the amount of MFRs in the ith year, kg hm⁻². D is the soil depth at which MPs appear, which is 0.4 m in this paper. ρ is soil bulk density, which is 1.44 × 10³ kg m⁻³ [46]. EF_j refers to the factor of releasing microplastics from the jth type film in the next 50 years, and EF₀ is the factor of historical PE film.

The microplastics emission resulting from wearing of plastic film is unavoidable in the process of production and use. Ren et al. [47,48] presented an effective approach to quantify the EF of microplastics by mechanical abrasion experiments. Although it still has limitations in the standpoint and range, there is no other reliable method for measuring the EF of microplastics. The calculation formula is shown as Equation (14) [47,48]:

$$EF={\displaystyle \frac{1-\frac{CLT}{c}exp(-d\times TK)-a}{b}}$$

(14)

where CLT is the light transmittance of the plastic film. The values for PE film and PBAT film are 90% in the next 50 years. TK is the film thickness of film (Table 1), and the thickness of PE film used in the past was 0.008 mm [10]. The variables a, b, c, and d, are modified parameters [47,48].

(2)

The cumulative amount of PAEs was calculated by Equations (13)–(17):

$$Q_{APES}=Q_{0APEs}+Q_{cAPES}$$

(15)

$$Q_{0 APEs}={\displaystyle \sum _{i=1}^n\frac{Q_0\times P_0}{D\times \rho \times {10}^4}}$$

(16)

$$Q_c{}_{PAEs}={\displaystyle \sum _{i=1}^n\frac{(U_{mi}-Q_i)\times P_j\times k}{D\times \rho \times {10}^4})}+{\displaystyle \sum _{i=1}^n\frac{Q_i\times P_j}{D\times \rho \times {10}^4}}$$

(17)

where Q_PAEs refers to the cumulative amount of pollution from PAEs, mg kg⁻¹. Q_0PAEs refers to the amount of PAEs released from historical MRFs, mg kg⁻¹. Q₀ is the historical accumulation of MFRs, kg hm⁻². P₀ is the amount of PAEs in historical film residues, 245 g kg⁻¹ [49]. Q_cPAEs refers to the increasing amount of PAEs released from cumulative MRFs in the future, mg kg⁻¹. U_mi refers to the amount of plastic film used in year i, kg hm⁻². Q_i is the amount of MFRs in the soil in the ith year, kg hm⁻², and i is the mulching time (y) of plastic film, from 1 to n. P_j is the amount of PAEs in film, and they are 13.4 mg kg⁻¹ and 32.5 mg kg⁻¹ in PE film and PABT film, respectively [49,50,51]. D is the soil depth at which PAEs appear, which was 0.4; ρ is the soil bulk density, which was 1.44 × 10³ kg m⁻³ [46]; and k is 16.3%, the coefficient of PAEs emission into the soil [21]. This calculation assumes that all PAEs are released into the soil over time, although this process requires a prolonged period. However, due to the lack of a more accurate estimation method, this approach remains the best available for estimation purposes.

3. Results

3.1. Effects of Management Strategies on Accumulation of Mulching Film Residues in the Future

3.1.1. Significant Differences in Increasing Trends of MFRs Under Different Strategies

The results indicate that the increasing trends of MFRs varied significantly across different policy scenarios over the next 50 years. MFRs increased more markedly with lower recycling rates, both when using PE film and PBAT film (Figure 1a,b). In the PE-S0 scenario, MFRs levels showed a continuous upward trend, surpassing the national standard limit of 75 kg hm⁻² within five years and reaching over 480 kg hm⁻² by the 50th year. In contrast, in PE-S1, PE-S2, and PE-S3 scenarios, the increase in MFRs was notably less, with final increasing values of 190 kg hm⁻², 142 kg hm⁻², 94 kg hm⁻², and 47.39 kg hm⁻², respectively, over 50 years. For PE-S1, PE-S2, and PE-S3, the 75 kg hm⁻² limit was exceeded in the 13th, 18th, and 43rd years, respectively. Notably, in PE-S4, MFRs accumulation at year 50 remained at 47 kg hm⁻², well below the national threshold (Figure 1a).

In scenarios utilizing PBAT film, MFRs accumulation was substantially lower than in PE film scenarios. In scenarios utilizing PBAT film, the increasing MFRs accumulation was substantially lower than in PE film scenarios, with respective values of 37 kg hm⁻², 16 kg hm⁻², 12 kg hm⁻², 8 kg hm⁻², and 4 kg hm⁻² in PBAT-S0, PBAT-S1, PBAT-S2, PBAT-S3, and PBAT-S4 scenarios by the 15th year. Additionally, MFRs levels stabilized after 15 years (Figure 1b). Overall, a PE film recycling rate of over 95% effectively reduced MFRs accumulation, though PBAT film use was even more effective.

3.1.2. Effects of Strategies on MFRs Accumulation Under Historical Conditions

The impact of different policies on MFRs accumulation in the future differed substantially depending on historical conditions. Under HC1, PE-S0, PE-S1, PE-S2, and PE-S3 strategies led to an increase in MFRs accumulation, reaching 499 kg hm⁻², 208 kg hm⁻², 160 kg hm⁻², and 113 kg hm⁻² by the 50th year, respectively. Conversely, PBAT-S0, PBAT-S1, PBAT-S2, and PBAT-S3 strategies initially showed an increase followed by a decline in MFRs accumulation. In PE-S4 and PBAT-S4 strategies, MFRs levels showed a decreasing trend, with final values of 66 kg hm⁻², 57 kg hm⁻², 33 kg hm⁻², 30 kg hm⁻², 26 kg hm⁻², and 22 kg hm⁻², all below the 75 kg hm⁻² threshold (Figure 1c,d).

In HC2, PE-S0, PE-S1, and PE-S2 strategies led to an accumulation of 519 kg hm⁻², 228 kg hm⁻², and 180 kg hm⁻², respectively. Under PBAT-S0, PBAT-S1, and PBAT-S2 strategies, MFRs accumulation showed an initial increase followed by a reduction, while under PE-S3, PE-S4, PBAT-S3, and PBAT-S4 strategies it displayed a decreasing trend. MFRs accumulations in PE-S3, PE-S4, and PBAT-S0 were, respectively, 133 kg hm⁻², 86 kg hm⁻², and 77 kg hm⁻², higher than 75 kg hm⁻² in the 50th year, and the accumulations further decreased to 54 kg hm⁻², 50 kg hm⁻², 46 kg hm⁻², and 42 kg hm⁻² in PBAT-S1, PBAT-S2, PBAT-S3, and PBAT-S4, respectively (Figure 1e,f).

Under HC3, PE-S0 and PE-S1 strategies caused MFRs to rise to 534 kg hm⁻² and 243 kg hm⁻², respectively. MFRs accumulation initially increased and then decreased in PBAT-S0 and PBAT-S1 strategies, whereas in PE-S2, PE-S3, PE-S4, PBAT-S2, PBAT-S3, and PBAT-S4 strategies it showed decreasing trends, with final accumulations of 195 kg hm⁻², 148 kg hm⁻², 101 kg hm⁻², 92 kg hm⁻², 68 kg hm⁻², 65 kg hm⁻², 65 kg hm⁻², 61 kg hm⁻², and 57 kg hm⁻², respectively, by the 50th year (Figure 1g,h).

Under HC4 and HC5, MFRs accumulation trends were consistent within each strategy. The PE-S0 strategy led to an increase in MFRs, reaching 553 kg hm⁻² and 577 kg hm⁻², respectively. PBAT-S0 strategy showed an initially increasing and then decreasing trend, while other strategies showed a downward trend, with MFRs accumulations remaining above 75 kg hm⁻² (Figure 1i–l). In summary, the PE-S0 strategy consistently resulted in a significant increase in MFRs under all historical conditions. The effectiveness of other strategies in reducing MFR pollution depended on prior accumulations; with lower historical MFRs levels, the effects of mitigation strategies were more obvious.

3.2. Effects of Strategies on Cumulative Ecological Effects of Mulching Film Residues

3.2.1. Cumulative Ecological Effects of Mulching Film Residues

Results demonstrated significant variations in CEEs under different strategies. In HC1, the CEEs index increased significantly under PE-S0, PE-S1, PE-S2, PE-S3, and PE-S4 strategies, particularly in PE-S0. Conversely, CEEs decreased under PBAT-S0, PBAT-S1, PBAT-S2, PBAT-S3, and PBAT-S4. Under PE-S0, CEEs rose from the low level to medium level by year 30, whereas in other strategies CEEs remained at the low level over the next 50-year period, as illustrated by index variations in Figure 2a. In HC2, the CEEs had an obvious increase under the PE-S0 strategy, reaching medium levels within 20 years from the low level. The increase under PE-S1, PE-S2, PE-S3, and PE-S4 was less pronounced than under PE-S0, while all PBAT strategies resulted in declines in CEEs, with remaining low levels across all strategies except PE-S0 in the future (Figure 2b). In HC3, CEEs increased to medium levels within 10 years under PE-S0 and reached medium levels under PE-S1 within 30 years. In contrast, CEEs decreased under PE-S3, PE-S4, PBAT-S0, PBAT-S1, PBAT-S2, PBAT-S3, and PBAT-S4, maintaining at low levels over the next 50 years (Figure 2c). In HC4, the CEEs under PE-S0 rose significantly, reaching the high level in the 40th year, with a smaller increase under PE-S1 and PE-S2. In other strategies, CEEs decreased to low levels in the 20th year (Figure 2d). In HC5, CEEs increased notably under PE-S0, reaching a high level within 20 years from medium levels. CEEs decreased under PE-S2, PE-S3, PE-S4, and PBAT-S0 strategies over the next 50 years, but they remained at medium levels, while under strategies PBAT-S1, PBAT-S2, PBAT-S3, and PBAT-S4, CEEs decreased to low levels by the 50th year (Figure 2e).

According to the significance analysis, under all historical conditions, there were significant differences in I_ce among all PE strategies, with the order being PE-S0 > PE-S1 > PE-S2 > PE-S3 > PE-S4 (p < 0.05), and the I_ce in PE-S0 was significantly higher (p < 0.05) than over the next 50 years. I_ce in PBAT-S0 were higher than PBAT-S1, PBAT-S2, PBAT-S3, and PBAT-S4 (p < 0.05). In the 10th year, I_ce in PBAT-S1 and PBAT-S2 were higher than PBAT-S3 and PBAT-S4 (p < 0.05), while I_ce in PBAT-S1, PBAT-S2, PBAT-S3, and PBAT-S4 had no significance (p > 0.05) in the 20th, 30th, 40th, and 50th year. Concerning the difference analysis between PE strategies and PBAT strategies, results showed that I_ce in PE-S0, PES-1, and PE-S2 were significantly higher than in all PBAT strategies over the next 50 years (p < 0.05). It is worth mentioning that there was no significance between PE-S3 and PBAT-S0 in the 10th year, and no significance between PE-S4 and PBAT-S0 in the 20th, 30th, 40th, and 50th years (p > 0.05) (Figure 3) in all historical conditions. In summary, CEEs of MFRs consistently and significantly increased under PE-S0 strategies in all historical conditions over the next 50 years. The effects of PE-S4 on inhibiting CEEs increase was more efficient than PBAT-S0 in the next 10 years, and they had no significance over the next 20 to 50 years.

3.2.2. Direct Ecological Effects of Mulching Film Residues

The analysis of direct ecological effects (I_de) revealed significant differences across strategies. In HC1, the initial I_de value of 0.12 increased by 565%, 177%, 114%, and 51% under PE-S0, PE-S1, PE-S2, and PE-S3, respectively. In PBAT-S0, PBAT-S1, PBAT-S2, and PBAT-S3 scenarios, I_de initially increased and then declined, while it showed a consistent decrease under PE-S4 and PBAT-S4, reaching reductions of 23%, 24%, 55%, 61%, 66%, and 71% in year 50 (Figure 4a). In HC2, PE-S0, PE-S1, and PE-S2 strategies led to increases in I_de, rising to 0.70 and 0.31 by year 50. Under PE-S3, PE-S4, PBAT-S0, PBAT-S1, PBAT-S2, PBAT-S3, and PBAT-S4, I_de decreased, reaching 0.21, 0.13, 0.12, 0.08, 0.08, 0.07, and 0.07, respectively (Figure 4b). In HC3, I_de increased under PE-S0 and PE-S1, reaching 0.83 and 0.38 from 0.34. In other strategies, I_de decreased to values of 0.33 (PE-S2), 0.26 (PE-S3), 0.19 (PE-S4), 0.17 (PBAT-S0), 0.14 (PBAT-S1), 0.13 (PBAT-S2), 0.12 (PBAT-S3), and 0.12 (PBAT-S4) by the 50th year (Figure 4c). In HC4 and HC5, I_de showed a similar pattern. Under PE-S0, I_de rose significantly, reaching 0.86 and 0.89 by the 50th year, increasing from 0.46 in HC4 and 0.62 in HC5. In HC4, reductions under all strategies except PE-S0 ranged from 13% to 75%, while in HC5, reductions were between 28% and 75% across different strategies (Figure 4d,e). In all historical conditions, PE-S0 resulted in an increase in direct ecological effects, while PBAT-S2, PBAT-S3, and PBAT-S4 showed consistent reductions over 50 years.

According to the significance analysis, the significant differences in I_de were PE-S1 > PE-S2 > PE-S3 > PE-S4 (p < 0.05), and the I_de in PE-S0 was significantly higher (p < 0.05) than them over the next 50 years under all historical conditions. I_de in PBAT-S0 was higher (p < 0.05) than PBAT-S1, PBAT-S2, PBAT-S3, and PBAT-S4 (p > 0.05) over the next 50 years. Moreover, I_de in PE-S0 and PES-1 were significantly higher than in all PBAT strategies over the next 50 years (p < 0.05). There was no significance between PE-S2, PE-S3, and PBAT-S0 in HC1, HC2, and HC3, and no significance between PE-S2 and PBAT-S0 in HC4 and HC5 in the next 10 years (p > 0.05). In the 20th, 30th, 40th, and 50th years, PE-S4 had no significance with PBAT-S0 (p > 0.05) in all historical conditions (Figure 5). Above all, the direct effects of MFRs consistently and significantly increased under PE-S0 strategies in all historical conditions over the next 50 years. The effect of PE-S4 on inhibiting the direct effects of MFRs increasing was better than PBAT-S0 in the next 10 years, and they had no significance over the next 20 to 50 years.

3.2.3. Indirect Ecological Effects of Mulching Film Residues

Trends of indirect ecological effects (I_ie) differed from I_de, as I_ie did not generally decrease across strategies. In HC1, I_ie, initially valued at 0.10, increased under all scenarios, with the most substantial rise in using PE film without recovery. By the 50th year, I_ie had increased by 260% (PE-S0), 139% (PE-S1), 113% (PE-S2), 83% (PE-S3), and 48% (PE-S4), while PBAT-S0, PBAT-S1, PBAT-S2, PBAT-S3, and PBAT-S4 resulted in smaller increases of 23%, 10%, 8%, 5%, and 3%, respectively (Figure 6a). In HC2, I_ie increased by 5% (PBAT-S1), 3% (PBAT-S2), 2% (PBAT-S3), and 1% (PBAT-S4), respectively. More significant increases were observed under PE-S0 (157%), PE-S1 (79%), PE-S2 (63%), PE-S3 (45%), PE-S4 (25%), and PBAT-S4 (12%) (Figure 6b). In HC3, I_ie stabilized at 0.29 under PBAT-S4, with minor increases under PBAT-S0, PBAT-S1, PBAT-S2, and PBAT-S3 strategies. In PE film strategies, I_ie increased notably, with values rising by 126%, 62%, 49%, 34%, and 18% (Figure 6c). In HC4, increases of I_ie ranged from 100% to 14% under PE-S0 to PE-S4 strategies, while I_ie rose by 6% (PBAT-S0), 3% (PBAT-S1), and 2% (PBAT-S2), remaining steady at 0.40 under PBAT-S3 and PBAT-S4 strategies (Figure 6d). In HC5, I_ie reached 0.98 from 0.53 under PE-S0, and rose by 37%, 29%, 20%, and 1% across PE film strategies, with PBAT-S0 and PBAT-S1 showing a 5% increase and 2% increase, and other PBAT strategies showing no change, stabilizing at 0.53 (Figure 6e). In conclusion, PBAT film use was more effective than PE film in controlling indirect ecological effects, with higher recycling rates further enhancing its efficacy, However, none of these strategies could reduce the indirect ecological effects.

The significant differences in I_ie showed PE-S1 > PE-S2 > PE-S3 > PE-S4 (p < 0.05), and the I_de in PE-S0 was significantly higher (p < 0.05) than them over the next 50 years under all historical conditions. I_de in PBAT-S0 was higher (p < 0.05) than PBAT-S1, PBAT-S2, PBAT-S3, and PBAT-S4 (p > 0.05) in HC1, HC2, and HC3 over the next 50 years and HC4, HC5 over the next 30 years. Further, I_de in PE-S0, PE-S1, and PE-S2 were significantly higher than in all PBAT strategies over the next 50 years (p < 0.05). There was no significance between PE-S3 and PBAT-S0 in HC1 to HC5 in the next 10 years, and no significance between PE-S4 and PBAT-S0 in the next 20 to 50 years (p > 0.05) (Figure 7). Above all, indirect effects of MFRs increased under all strategies in all historical conditions over the next 50 years. The increase in indirect effects under PE strategies was more significant than under PBAT strategies. The effect of PE-S4 on inhibiting the indirect effects of MFRs increasing was better than PBAT-S0 in the next 10 years, and they had no significance over the next 20 to 50 years.

4. Discussion

4.1. Effectiveness of Strategies on Mitigating Mulching Film Residues Pollution

The results indicated that both increasing the recycling rate of PE film and utilizing PBAT film effectively curbed MFRs accumulation over the next 50 years, with higher recycling rates yielding better results. When the recycling rate exceeded 95%, the increase in PE MFRs remained below 75 kg hm⁻², similar to PBAT film usage. Additionally, MFRs accumulation declined across all historical conditions. Conversely, using PE film without recovery resulted in a yearly increase of 17.74 kg hm⁻² in residual film, aligning with previous studies [52,53]. However, the total increase in MFRs over the next 50 years would reach 480 kg hm⁻² without recovery, mainly due to the natural degradation rate of PE film (2.8%) considered in the calculation [30]. That was why total MFRs accumulation over the next 50 years showed decreasing trends in different historical conditions while the yearly increase in MFRs continued.

Moreover, PBAT film appeared to be more effective than higher PE recovery rates both in reducing MFRs accumulation and in the release of MPs and PAEs. As shown in Figure 1a, only when the PE recovery rate exceeded 95% did the MFRs increase amount remain below 75 kg hm⁻², while the increase amounts were below this threshold under all PBAT strategies (Figure 1b). Notably, MPs released from PE residues reached as high as 561.9 g kg⁻¹ without recovery, whereas PE film with a 95% recovery rate releases 55.4 g kg⁻¹ MPs. In contrast, PBAT MPs amount to 24.5 g kg⁻¹ without recovery, less than half of released amount of PE MPs at a 95% recycling rate (Figure 8a,b). PAEs released from PBAT residues exceeded those from PE residues but remained within safe concentrations (Figure 8c,d). This aligned with recommendations by numerous countries and organizations advocating biodegradable film adoption [29,40]. This is contingent on PBAT’s economic feasibility for farmers. Alternatively, achieving a 95% recycling rate for PE film could effectively keep MFRs levels near threshold in arid areas over the next 50 years.

4.2. Indirect Ecological Effects Require More Attention than Direct Effects in the Future

MFRs negatively impact soil health, leading to degradation of soil properties and increased risks. The results suggest that increasing the recycling rate of PE film and utilizing PBAT film measures can alleviate soil property degradation caused by MFRs. Nonetheless, MPs and PAEs pollution from MFRs would increase, either under the strategies of higher PE recycling rates or under using PBAT film strategies. Although MPs concentrations were remarkably out of safe levels when using PBAT, they were notably lower than those from PE film. However, studies by Uzamurera et al. and Zhou et al. suggested that MPs released from biodegradable films may actually exceed those from PE films [54,55]. This discrepancy may stem from differences in calculation methods and parameters. Given this, MPs from PBAT films may be underestimated, warranting further attention in research and production [33]. Unlike MPs, the increase in PAEs from residual films over the next 50 years is much lower and within safe levels across all scenarios (Figure 8c,d). Nevertheless, historical accumulations have already exceeded safe limits, except in HC1, posing persistent risks to the soil environment (Figure 8e,f) [28,41].

Additionally, many studies have shown that micro/nanoplastics can be absorbed and transported to other organs and even edible parts of plants through transpiration [22,24,56]. Furthermore, the “plastisphere” formed by MPs may combine with organic pollutants and heavy metals, thereby contaminating the food chain [20,22,56,57]. This process poses potential risks to crop quality, with possible bioaccumulation in humans and animals [28,58,59]. PAEs also accumulate in crops, with potential transfer along the food chain [41,59]. These results corroborate findings that MFRs would lead to long-term environment hazards, meaning that the indirect ecological effects require more attention in the future [7,32,55].

4.3. Uncertainties and Limitations

In order to simulate the variation in the accumulation of MFRs and assess the ecological effects of MFRs over the next 50 years under different management strategies, this study used a simple and direct method to calculate the accumulation of MFRs [60]. However, there are some uncertainties in the parameters. The parameter F_r includes current and ideal values. The current value of F_r referred to “Manual for Mulching Film Residue Coefficient”, which was obtained through field sampling by the Compilation Committee of the First National Pollution Source Census [35], and it was considered to be reliable. However, the ideal values of F_r (20%, 15%, 10%, and 5%) are the values that managers and farmers are trying to achieve through various measures aiming to reduce residual film pollution in farmland and promote the agriculture sustainability [30]. Another uncertain parameter is F_m, which is mainly due to the quality of film from different producers, and related to the subjectivity of farmers in its usage. We used the commonly used amounts of 60 kg hm⁻², 65 kg hm⁻², 70 kg hm⁻², 75 kg hm⁻², and 80 kg hm⁻² as replications in order to make the results more reliable [10,31,32]. In addition, the degradation rates of PE and PBAT film residue were considered in the calculation of MFRs accumulation, and the d_r used referred to the ideal value in the standard manual [36,37], while the real d_r may differ in different regions and environments [54,61,62]. Those uncertainties should be analyzed and assessed to determine how they influence the results in the future [7,55]. Further, the estimation model calculating the amount of MFRs could be optimized by optimizing these parameters.

A comprehensive assessment of MFRs impacts can help inform policy decisions and management strategies. This study developed an evaluation index system for CEEs of MFRs to assess the impacts of MFRs on farmland ecosystems [9]. Key indicators included changes in soil water evaporation, water infiltration, organic matter content, effective phosphorus content, and crop yield reduction rates to represent direct ecological effects [8,9,18,19,21], while MPs and PAEs accumulations were used to reflect indirect ecological effects [9,28,40]. This dual-index approach enhances assessment accuracy. However, there are limitations in evaluating the CEEs of MFRs. First, soil biology and enzyme activities, significant ecological factors influenced by MFRs, were not included, mainly because of divergences among different research results [59,60,63]. Secondly, the indirect effects of MFRs are supposed to encompass MPs generated during MFRs degradation and the “plastisphere effect” due to the release or adsorption of organic matter and heavy metals [64,65,66]. Although there has been a lot of laboratory research conducted in these fields, those conclusions are significantly different, and it is difficult to unify and include them in this comprehensive evaluation [28,59,65]. As a result, this study comprises a tentative exploration of the comprehensive assessment of indirect effects of MFRs, primarily focused on MPs and PAEs accumulation, without accounting for other potential risks. In the future, more research should be conducted to refine the evaluation system of the cumulative ecological effects of MFRs [9]. Specifically, the effects of different plastic fragments on soil biology and enzyme activity warrant further investigation, as does the exploration of the “plastisphere effects” in agricultural systems [27,39,66].

5. Conclusions

This study analyzed the impact of different strategies on MFR pollution by estimating the accumulation and assessing cumulative ecological effects of MFRs over the next 50 years. Results indicated that the increasing amount of MFRs would be 480 kg hm⁻² without any recovery of PE film, and it would be 190 kg hm⁻², 142 kg hm⁻², 95 kg hm⁻², and 47 kg hm⁻² with PE film recovery rates of 80%, 85%, 90%, and 95% over the next 50 years. In contrast, the increase in MFRs would be 39 kg hm⁻² at most when using PBAT film. The 95% recovery rate of PE film strategy and using PBAT film strategies could work well in reducing MFRs in soil in all historical conditions. Under the strategy of using PE film without recovery, the CEEs would intensify significantly. In comparison, increasing PE recovery rates and using PBAT film could curb these impacts over the next 50 years. Notably, under historical conditions of 75 kg hm⁻² and 160 kg hm⁻², CEEs remained low, while at 220 kg hm⁻², CEEs decreased from medium to low levels. Under 300 kg hm⁻² and 400 kg hm⁻² conditions, CEEs stabilized at medium levels, avoiding escalation to high levels. Specifically, the CEEs of MFRs could maintain the current status or decrease under the strategy of 95% recovery rate of PE film and using PBAT film, similar to the variation of direct effects. With the increase in accumulated MFRs, the indirect effects of MFRs increase; however, the indirect effects would not decrease with a reduction in MFRs accumulation due to ongoing microplastics’ and phthalate esters’ release from residual films. In conclusion, a 95% recovery rate of PE film and the use of PBAT films are most effective in mitigating plastic pollution in arid areas. Furthermore, the indirect ecological effects of MFRs cannot be neglected in the future as they pose a potential threat to crops, animals, and human beings. These results could provide a theoretical support for agricultural sustainable development in arid regions.