Biodegradable Plastic Mulch Research Articles

Soil Microbial Biomass and Microarthropod Community Responses to Conventional and Biodegradable Plastics

Plastic mulch is a commonly employed technique in agriculture to enhance crop production. Given the persistence of plastic residues in soil, bioplastics offer a potential alternative. Unfortunately, little is known about the medium-term consequences of both plastic and bioplastic mulches on soil properties. This study aimed to assess the medium-term consequences of plastic and bioplastic mulches and their replacement on soil properties. To this aim, the impact of conventional plastic (polyethylene, CP) and biodegradable plastic (BP) mulches on soil’s abiotic (pH, water content, total and organic carbon and total nitrogen contents) and biotic (microbial biomass, microbial respiration, enzymatic activities and microarthropod communities) properties after 2 years of exposure (T1) and after 3 (T2) and 6 (T3) months of mulch replacement was investigated. Moreover, uncovered soils were assessed as a control. The results highlighted that the samples were more significantly impacted by exposure time to mulches than by the different kinds of mulches. The replacement of both mulches (T2 and T3) decreased the content of C and increased the microbial biomass and activities; moreover, the mulch replacement changed the microarthropod community composition with a decrease of Collembola and an increase of Oribatida and Gamasida, especially in soils covered by biodegradable plastic mulches. Further investigations are needed to better understand the long-term impact of mulches on soil biota in order to prove the potential ecological implications of transitioning to sustainable alternatives.

Field-based assessment of the effect of conventional and biodegradable plastic mulch film on nitrogen partitioning, soil microbial diversity, and maize biomass

In an agricultural context, the use of conventional low-density polyethylene (LDPE) and biodegradable plastic mulch film has been actively promoted, however, the effects on physical and biochemical soil properties, crop growth dynamics, yield, and nutrient cycling of conventional and biodegradable mulch film use in a temperate climate remain largely undetermined. Here, we conducted a field experiment, exploring the effects of no mulch (control), conventional (LDPE), and biodegradable (PLA/PBAT) plastic mulch film on soil and crop (Zea mays L.) nitrogen (N) partitioning after application of 15N-labelled ammonium-nitrate fertiliser. Further, we also investigated the treatment effects on soil physical and biochemical properties (e.g., microbial diversity, compound-specific microbial 15N incorporation, N dynamics), plant development, as well as monitoring the biotic and abiotic degradation of the plastic mulch films. We found that conventional mulch film increased crop yield by 25 % and 15N uptake by 34 % compared to the control, simultaneously reducing 15N retention by 40 % in the topsoil (0–10 cm), but not affecting microbial N use efficiency and N transformation and incorporation into the protein pool. Biodegradable film application resulted in similar biomass (306 ± 14 g plant−1) to both control (275 ± 14 g plant−1) and conventional mulch (344 ± 20 g plant−1) treatments, but significantly reduced 15N crop uptake by 63 % compared to the conventional mulch film. We ascribe this to the accelerated mechanical breakdown and faster degradation of the biodegradable mulch film during the growing season. These findings suggest that current biodegradable plastic mulch film polymer blends may not be a suitable alternative to conventional mulch film in terms of short-term productivity and N use efficiency in a temperate climate for maize production.

Changes in Soil Microbial Communities Induced by Biodegradable and Polyethylene Mulch Residues Under Three Different Temperatures

Mulching is a common method increasing crop yield and achieving out-of-season production; nevertheless, their removal poses a significant environmental danger. In this scenario, the use of biodegradable plastic mulches comes up as a solution to increase the sustainability of this practice, as they can be tilled in soil without risk for the environment. In this context, it is important to study the microbial response to this practice, considering their direct involvement in plastic biodegradation. This study evaluated the biodegradation of three commercial mulch residues: one conventional non-biodegradable mulch versus two biodegradable ones (white and black compostable Mater-Bi mulches). The experiment was conducted under three incubation temperatures (room temperature 20–25 °C, 30 °C, and 45 °C) for a 6-month trial using fallow agricultural soil. Soil without plastic mulch residues was used as a control. White mater-bi biodegradable mulch residues showed higher degradation rates up to 88.90% at 30 °C, and up to 69.15% at room temperature. Furthermore, incubation at 45 °C determines the absence of degradation for all types of mulch considered. Moreover, bacterial alpha diversity was primarily influenced by plastic type and temperature, while fungal populations were mainly affected by temperature. Beta diversity was impacted by all experimental variables. Predicted functional genes crucial for degrading complex substrates, including those encoding hydrolases, cutinases, cellobiosidases, and lipases, were derived from 16S rRNA gene sequencing data. Cluster analysis based on predicted enzyme-encoding gene abundance revealed two clusters, mainly linked to sampling time. Finally, core microbiome analysis identified dominant bacterial and fungal taxa in various soil-plastic ecosystems during degradation, pinpointing species potentially involved in plastic breakdown. The present study allows an assessment of how different temperatures affect the degradation of mulch residues in soil, providing important insights for different climatic growing zones. It also fills a gap in the literature by directly comparing the effects of biodegradable and polyethylene mulches on soil microbial communities.

Innovative approach of biodegradable mulches in sustainable agriculture for crop production and environmental conservation

The use of biodegradable plastic mulches in place of conventional plastic mulches in agriculture has been suggested as being more ecologically friendly. However, a number of obstacles, including concerns about performance and cost, have inhibited their implementation. In this study, we set out to determine the impact of biodegradable film mulches on plant production, crop yield, sustainability, nutrient supply, environment, cost-effectiveness, pros and cons with innovative approach. The material and method used in this study include the application of a literature review on biodegradable mulch (BDM) film. According to our findings, the biodegradable film mulch greatly outperformed the plastic mulch in terms of soil health, water use, nutrient availability, and microbial activity. These results imply that biodegradable film mulch has the potential to decrease plastic waste in agriculture while increasing soil health and crop output. In conclusion, using biodegradable film mulch with using innovative approach in agriculture might be an effective means to alleviate the environmental problems brought on by conventional plastic mulches.

Mineralisation and priming effects of a biodegradable plastic mulch film in soils: Influence of soil type, temperature and plastic particle size

There is increasing use of biodegradable mulch films (BDMs) as an environmentally sustainable alternative to traditional mulch films in agriculture. However, their degradation fate and priming effect (PE) on native soil organic matter (SOM), including in the form of microplastics (MPs) after disintegration, are not well known. In this study, we investigated mineralisation of a BDM (0–2000 μm MPs) and its PEs in three soils, i.e., a Ferralsol, a Vertisol and a Solonetz. The MPs were incubated at a concentration of 0.8% (w/w) separately in the three soils at three temperatures i.e., 20, 30 and 40 °C for 150 days. We also evaluated the effect of BDM MP particle size on its mineralisation and PEs in two soils (a Ferralsol and a Vertisol). Six size fractions (i.e., <100, 100–250, 250–500, 500–1000, 1000–2000, 2000–4750 μm) were incubated in the soils at 30 °C for 150 days. A δ13C technique was employed to determine the proportion of C mineralised from MPs and SOM owing to their distinct δ13C values. Temperature, soil type, particle size and their interactions were all key factors in the mineralisation of MPs and PEs. The mineralisation of MPs increased with the increasing temperatures from 20 to 40 °C in the three soils over time with few exceptions. At 20 and 40 °C, the Ferralsol with greater carbon and clay content showed greater MP mineralisation than the Vertisol and Solonetz. Opposite trends were observed for the MP mineralisation and PEs in the Vertisol at 20 and 30 °C and in the Ferralsol at 20 °C. However, at 40 °C, both MP mineralisation and PEs exhibited similar trends in the three soils suggesting that a ‘co-metabolism’ may be dominant at high temperatures. Furthermore, we observed that smaller MPs tended to induce greater mineralisation, whereas the larger MPs caused greater PEs than small particles.

Are biodegradable plastic mulch films an effective way to solve residual mulch film pollution in farmland?

Are biodegradable plastic mulch films an effective way to solve residual mulch film pollution in farmland?

Organic and inorganic nitrogen amendments reduce biodegradation of biodegradable plastic mulch films

Abstract. Biodegradable mulch films (BDMs) are a sustainable and promising alternative to non-biodegradable polyethylene mulches used in crop production systems. Nitrogen amendments in the form of fertilizers are used by growers to enhance soil and plant-available nutrients; however, there is limited research on how these additions impact the biodegradation of BDMs tilled into soils. A 4-month laboratory incubation study using soil microcosms was used to investigate the effects of inorganic (ammonium nitrate) and organic (urea and amino acids) nitrogen application on biodegradation of BDMs. We investigated the response of soil bacterial, fungal, and ammonia-oxidizing microbial abundance along with soil nitrogen pools and enzyme activities. Microcosms were comprised of soils from two diverse climates (Knoxville, TN, USA, and Mount Vernon, WA, USA) and BioAgri, a biodegradable mulch film made of Mater-Bi®, a bioplastic raw material containing starch and poly(butylene adipate-co-terephthalate) (PBAT). Both organic and inorganic nitrogen amendments inhibited mulch biodegradation, soil bacterial abundances, and enzyme activities. The greatest inhibition of mulch biodegradation in TN soils was observed with urea amendment where biodegradation was reduced by about 6 % compared to the no-nitrogen control. In WA soils, all nitrogen amendments suppressed biodegradation by about 1 % compared to the no-nitrogen control. Ammonia monooxygenase amoA gene abundances were increased in TN soils in all treatments but reduced for all treatments in WA soils. However, a significantly higher nitrate concentration and a lower ammonium concentration were seen for all nitrogen treatments compared to no-nitrogen controls in both TN and WA. This study suggests that the addition of nitrogen, particularly inorganic amendments, could slow down mulch biodegradation but that mulch biodegradation does not negatively affect soil nitrification activity.

Soil Microclimate and Persistence of Foodborne Pathogens Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella enterica Newport in Soil Affected by Mulch Type

Mulching is a common agricultural practice that benefits crop production through soil moisture retention, weed suppression, and soil temperature regulation. However, little is known about the effect of mulch on foodborne pathogens present in soil. In this study, the influence of polyethylene plastic, biodegradable corn-based plastic, paper, and straw mulches on Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella enterica Newport populations in soil was investigated. Silt loam soil in troughs was inoculated with a cocktail of the pathogens and covered with mulch or left bare, then incubated for 21 days, during which bacteria were enumerated and environmental parameters monitored. Bacterial counts declined in all treatments over time (p < 0.001) but persisted at 21 days at 0.8–0.95 log CFU/g. Pathogens also declined as a factor of mulch cover (p < 0.01). An exponential decay with asymptote model fit to the data revealed slower rates of decline in soil under mulches for all pathogens (p < 0.05) relative to bare soil. Compared to the average for all treatments, rates of decay in bare soil were 0.60 (p < 0.001), 0.45 (p < 0.05), and 0.63 (p < 0.001) log CFU/g/d for E. coli O157:H7, L. monocytogenes, and Salmonella, respectively. Linear multiple regression revealed that soil hydrological parameters were positively correlated (p < 0.05) with bacterial counts, while day soil temperatures were negatively correlated (p < 0.001), suggesting that higher day temperatures and lower moisture content of bare soil contributed to the faster decline of pathogens compared to mulched soil. A microcosm experiment using field soil from lettuce cultivation suggested no influence of prior mulch treatment on pathogens. In summary, pathogen decline in soil was modified by the soil microclimate created under mulch covers, but the effect appeared was restricted to the time of soil cover. Slower decline rates of pathogens in mulched soil may pose a risk for contamination of fresh market produce crops.

A review of soil pollution from LDPE mulching films and the consequences of the substitute biodegradable plastic on soil health

The plastic film mulching system has a significant role in increasing crop grain yields by changing the microenvironment of the plant. On the other hand, plastic mulching materials pollute the land and water because they are not degraded or disposed of properly. Biodegradable plastic mulches (BPM) may be used as a substitute for conventional low-density polyethylene (LDPE) to protect soil health. In this review, the effect of micro(nano)plastics on soil health and function has been discussed in light of their distribution in soil, changes in soil biochemistry, interactions between microplastics with soil microbes and plants, and their growth patterns. The nano-plastics are now incorporated into the food chain from the soil through plants and finally harm the whole ecosystem, including humans. The use of BPM has been practiced recently, but only 1% of the world’s total plastic production is from biodegradable materials. In the second part of the review, the confusing terms "bio-based" and "biodegradable" were clarified based on their polymeric constituents. The physical parameters of different constituent materials for mulching purposes and their capability for sustainable solarization have been discussed. The effect of biodegradable mulches on soil health and other ecotoxic effects on plants, soil microorganisms, and other soil dwellers like Daphnia magna, Vibrio fischeri bacteria, green algae, slime mould, protozoa, invertebrates like earthworms, and common water fleas have been focused on in this review. In conclusion, the use of BPM for mulching purposes was reported to improve crop quality and yield and reduce weed growth in comparison to naked soil. The recent short-term studies ensured that mulches stayed unbroken throughout the growing season. But simultaneously, the biodegradable mulches affect soil health and have a substantial impact on physical parameters such as soil pH, electrical conductivity, aggregate stability, infiltration, nitrate-N, exchangeable potassium, etc. Therefore, a lot of long-term research is required for the use of BPM as a substitute for conventional LDPE as a mulching film in the agricultural field.

Biodegradable plastic mulch films increase yield and promote nitrogen use efficiency in organic horticulture

Plastic film mulches (PFM) are used extensively due to their ability to increase yield and suppress weed emergence. Their effects on plant-soil-microbial interactions, however, are less well understood. Organic systems rely on the supply of nutrients from organic sources (e.g., manures and fertility-building leys) and where poor N availability often limits yield. The issue is compounded by horticultural crops (e.g., lettuce) with a high N demand, but which are inefficient at recovering N from soil. The effect of PFM on the mineralisation of organic fertilisers and its interaction with other agronomic factors such as planting density is also less well-researched. We hypothesised that biodegradable PFM would be a useful tool to increase the efficiency of N management in organic horticulture by increasing the supply of available N leading to increased crop N uptake and crop yield, and simultaneously reducing N losses during the growing season. We conducted two field experiments under a temperate maritime climate with lettuces grown with either conventional (LDPE) PFM or a polylactic acid-based biodegradable PFM alongside un-mulched controls. The first experiment involved black or white coloured PFMs and two planting densities while the second experiment involved treatments with and without addition of poultry manure. Overall, yields were increased by 39% in both experiments with PFM, while soil mineral N concentrations were up to 5 times higher with PFM than without. Measurements of soil organic matter (SOM) turnover (Tea Bag Index) and soil CO2 efflux indicated a more rapid decay of SOM in the presence of the PFM. The use of PFM also promoted N use efficiency (NUE) by 300% in the presence of poultry manure. Denser planting with PFM resulted in proportionately higher yields. Higher yield and higher N concentrations (5-10%) in crop tissue in mulched plots resulted in higher total N uptake, however, total N uptake was low compared to soil concentrations: mulching with biodegradable PFM resulted in higher residual mineral N than un-mulched plots (77-147 mg kg-1 vs. 19 -70 mg kg-1). Our results are consistent with reduced N losses to the environment during the growing season and increased mineralisation under PFM. In conclusion, our findings support the adoption of PFM for organic horticulture and show that biodegradable PFM perform similarly to LDPE-based PFMs.

Effects of Biodegradable Plastic Mulch Film on Cabbage Agronomic and Nutritional Quality Traits, Soil Physicochemical Properties and Microbial Communities

The long-term use of polyethylene mulch (PEM) films can cause plastic film residual pollution that has an adverse effect on soil health and crop quality. To address this issue, poly(butylene adipate-co-terephthalate) (PBAT), an aliphatic–aromatic copolyester, is widely used in the production of commercially biodegradable plastic mulch (BDM) films. The use of BDMs can alleviate soil plastic pollution and reduce the labor cost of retrieving plastic film residues from the field. The effects of BDM and PEM on the agronomic and nutritional quality traits of cabbage cultivar ‘Sugan No. 35’, as well as the physicochemical properties and microbial communities of the soil were analyzed during two consecutive years of the experiment. No significant difference was observed in the cabbage agronomic and nutritional quality traits among three mulching treatments. Nonetheless, the mulching and degradation of BDM reduced the pH value and increased the organic matter content of the soil samples compared with PEM mulching. In the soil bacterial and fungal communities, Proteobacteria and Ascomycota were the most abundant bacterial phylum and fungal phylum across all the soil samples, respectively; the use of BDM increased the relative abundance of soil Proteobacteria and Ascomycota compared with PEM mulching. The overall cost of BDM mulching was much lower than that of PEM mulching during the cabbage production.

Soil Bioplastic Mulches for Agroecosystem Sustainability: A Comprehensive Review

The use of plastic mulch films is widespread in agriculture for specialty cropping systems because of several benefits. In this article, we critically review, for the first time under a holistic approach, the use of biodegradable plastic mulches (BdPMs) in soil as a sustainable alternative to conventional petroleum-based plastics, highlighting the current state of understanding of their degradation in soil and their effect on soil microorganisms, weed control, and soil properties. In addition, we provide a detailed focus on the history and economic importance of mulching. BdPMs are effective for use in vegetable production in that they improve physical, chemical, and biological soil properties, as well as enhancing microbial biodiversity, controlling weeds, and maintaining soil moisture. BdPMs could be useful to limit the use of agrochemicals and reduce tillage and irrigation supplies for sustainable management.

Evaluating and managing the sustainability performance of investments in green and sustainable chemistry: Development and application of an approach to assess bio-based and biodegradable plastics

The state of the world urgently calls for a transition toward production and consumption partners that can support a carbon-neutral, circular and sustainable economy. Green and sustainable chemicals, especially, biodegradable and bio-based plastics, are key components of this transition. However, significant financial investments are required for the implementation of green and sustainable chemistry principles and the broader promotion of sustainability. In this regard, the financial sector needs sound approaches to assess the sustainability of investments. With this paper, we show an approach to assess the environmental performance of investments through key performance indicators calculated based on life cycle assessment. The approach is applied for the assessment of a fictitious investment aimed at financing bio-based and biodegradable plastic mulch films. The performance is assessed by comparing changes induced by the investment, compared with what would have happened without the investment (i.e., using fossil-based plastic mulch films). The application of the approach shows that the investment could be in general favourable from an environmental point of view, in particular for the promotion of a more circular and low-carbon economy. The approach could be easily adapted to reflect the specificities of a wide range of investments. However, it should be noted that other environmental, economic, and social aspects may need to be integrated to depict the sustainability performance of investments in a more comprehensive manner.

Mulch film: An overlooked diffuse source of organic ultraviolet absorbers in agricultural soil

Ultraviolet absorbers (UVAs) are emerging pollutants of concern owing to their environmental persistence and endocrine-disrupting effects. UVAs are added to agricultural films to prevent UV-induced degradation, potentially leading to the release of UVAs into the soil. In this study, the occurrence of four frequently used UVAs (UV-324, UV-326, UV-328, and UV-531) in film-mulched agricultural soils (using conventional polyethylene films and biodegradable films) was investigated. Results showed that the UVA concentrations were several orders of magnitude higher in film-mulched soil (mean 91.4 μg/kg) than in unmulched soil (mean 0.08 μg/kg), indicating that mulch films are important sources of UVAs released into agricultural soil. Notably, the mean UVA concentration was up to 10 times higher in biodegradable-film-mulched soils than in polyethylene (PE) film-mulched soils; this result is consistent with our finding that the mean UVA concentration was 448 times higher in commercial biodegradable films than in PE films. In simulated migration experiments, UVAs migrated more readily into the soil from the biodegradable film than from the PE film. To our knowledge, this is the first report demonstrating that the use of mulch films may cause the accumulation of UVAs in agricultural soils as non-point sources. In particular, biodegradable plastic mulches can release more UVAs into soils.

Degradation Pattern of Five Biodegradable, Potentially Low-Environmental-Impact Mulches under Laboratory Conditions

The use of biodegradable (BD) plastic mulch materials as alternatives to the widely used low-density polyethylene (PE) is increasing nowadays, mainly for environmental reasons. However, the success of these materials depends, in addition to fulfilling their function, on completely degrading in the short term, which depends on both their composition and environmental conditions. This study focused on the degradation pattern of five BD plastic materials of different composition (i.e., corn and potato starch, and polylactic acid plastic (PLA) films, blended with different copolyesters during their manufacture), in two soils with different granulometry (Soil 1 has less clay content than Soil 2), taken from organic vegetable fields under controlled laboratory conditions. Conventional PE was used as a reference. The degree of degradation was evaluated through the number of fragments, weight loss, and surface area loss until their total disappearance. The degradation trend of the BD materials was similar in both soils, although much faster in Soil 2. Their total visible disappearance was in the following ranges: potato starch, 225–250 days in Soil 1, 150–200 days in Soil 2; corn starch, 550 days in Soil 1, 300 days in Soil 2; PLA, 1000–1050 days in Soil 1, 350–475 days in Soil 2. PE remained practically intact in both trials. The degradation model of potato starch materials fitted a decreasing exponential model in both soils, while the other bioplastics followed a decreasing Gompertz model, in all cases with steeper slopes in Soil 2. The curves of the degradation models indicated how the same material can degrade differently depending on the type of soil, information that could be useful for users and manufacturers in the framework of a sustainable agriculture.

Impact of buried debris from agricultural biodegradable plastic mulches on two horticultural crop plants: Tomato and lettuce

Biodegradable mulches (BDM) are increasingly valued and used for substituting non-biodegradable plastic mulches polluting agricultural soils. They are tilled into soil, where they fragment and release compounds throughout their biodegradation. The consequences of BDM use on the plant-soil environment have been partially studied with pristine and with artificially-weathered BDM fragments. However, to guarantee safety use of BDM, studies on the BDM debris effects are required. For this, to determine potential effects of the field-weathering BDM on plants, a mesocosm experiment was performed by sowing seeds from two major plant species commonly cultivated with BDM, tomato (Lycopersicon esculentum) and lettuce (Lactuca sativa), in plant pots containing pristine and field-weathered pieces from seven different BDM formulations, one paper mulch, a polyethylene (PE) mulch, and no-mulch control pots.Germination of both plant species was unaffected by any of the mulch treatments; however, PHB (polyhydroxybutyrate)-based BDM fragments severely inhibited tomato and lettuce plant growth, 90 and 95 %, respectively. Moreover, all pristine and field-weathered BDM significantly delayed lettuce plant development. Tomato plant growth progressed better, but growth retardation was also evidenced with most field-weathered BDM treatments. Overall, field-weathered fragments caused stronger effects on plants than the pristine unused ones. No effects were found for PE mulch, either pristine or field-weathered. The obtained results highlight that BDM debris may alter plant development depending on their nature and on their weathering, rather than on their physical presence, and evidence the need to conduct further experiments on the impact of field-weathered BDM on the plant-soil environment.

Degradation of polylactic acid/polybutylene adipate films in different ratios and the response of bacterial community in soil environments

Biodegradable plastic mulch film (BDM) is an environmentally friendly alternative to conventional polyethylene mulch, and has been growingly used in agriculture. However, practical degradation performance of BDM, especially the widely used type of blended polylactic acid (PLA)/polybutylene adipate (PBAT) in different ratios, and microbial alteration in soil environments, remain largely unrevealed. In this study, four types of BDM blended with 40–80% PLA and 20–60% PBAT were comparatively investigated through microcosm soil incubation experiments for 105 days, and combined with conditions of different soil moisture or pH. Microbiome within film-surrounding soil were assayed using 16 S rRNA high-throughput sequencing. Results showed a trend of increasing degradation efficiency with the increase of PLA proportion, and 70% PLA and 30% PBAT group presented the highest weight loss rate, i.e., 60.16 ± 5.86%. In addition, degradation and aging of PLA/PBAT varied among different soil moisture and pH values. A moderate moisture, i.e., 60% and a neutral pH7.0 caused significantly high degradation efficiency compared to other moisture or pH conditions. Moreover, bacterial abundance and community structure in the surrounding soil were related to soil moisture and pH. PLA/PBAT incubation treatment induced a remarkable increase in abundance of degradation-related species Pseudomonas and Sphingomonas. Bacterial richness and diversity in soil correspondingly respond to ratio-different PLA/PBAT's degradation under moisture/pH-different conditions through a redundancy analysis. Altogether, these findings indicate that practical degradation of PLA/PBAT film is closely related to soil environments and bacterial community. It is significant for the application of biodegradable plastics in agriculture on the perspective of soil sustainability.

Microplastic presence significantly alters soil nitrogen transformation and decreases nitrogen bioavailability under contrasting temperatures.

Plastic mulch is frequently used to increase crop yield, resulting in large quantities of residues accumulating in soil due to low recovery rates. However, the effects of microplastic residues from traditional and biodegradable plastic films on soil nitrogen (N) transformation and bioavailability are not well understood. Here, the main objectives were to examine the effects of micro-sized residues (diameter <5mm) of polyethylene (PE) and biodegradable plastic mulch films (PLA) on the soil N in two contrasting soils (clay soil and sandy loam soil) in different temperatures (15°C vs. 25°C). Results showed that the microplastic presence showed a little effect on soil N transformation and bioavailability at 15°C, but both microplastics significantly decreased NO3-, mineral N (MN), total dissolved N (TDN), the net cumulative N nitrification (Nn), and the net cumulative N mineralization (Nm) at 25°C, indicating that microplastics decreased soil N bioavailability at elevated temperature. Meanwhile, the microplastics significantly reduced the temperature sensitivity (Q10) of N mineralization. The presence of microplastics changed the composition of soil mineral N with lower relative NO3- and higher NH4+ compared to the control in clay soil. The sandy loam soil was more susceptible to microplastic pollution compared to clay soil in N transformation, due to different textures and biochemistry properties in the two soils, which showed that microplastics have a significant soil heterogeneity-dependent effect on soil N processes. Therefore, the results underline that the effects of microplastic residues on soil N cycling can be partly linked to soil properties, suggesting the urgent need for further studies examining their impacts on soil nutrient cycling in different soil systems.

An update on polyethylene and biodegradable plastic mulch films and their impact on the environment

Many ways are being developed in the realm of agriculture to increase crop yield while inflicting minimal damage to the soil and environment. One among them is the application of agricultural, biodegradable mulch (BDM) films. Organic substances or synthetic materials are used for making mulches. Also, bio-based polymers derived from bacteria, microorganisms, or fossil fuels are used to make BDM films. BDM films are used in crop production because of their high agronomical advantages which lead to sustainable agriculture. These films are placed on the soil's surface, around the plants. Mulches help in conserving the moisture, control the temperature of the soil, control the growth of the weed, and help in the utilization of soil nutrients thus, overall enhancing the crop yield. The usage of plastic mulch in agriculture has expanded substantially all around the world, over the past ten years, this is because polyethylene films are cheaper, easily produced, highly flexible, and durable. However, the improper disposal of used plastic films has resulted in soil pollution and environmental contamination. Traditional mulches are replaced by BDM, which is a more environmentally friendly alternative. After being used, degradable mulch films could be tilled into the soil and are expected to disintegrate over time. This review focuses on the BDMs, their history, plastic mulches, how BDMs became an alternative source for plastic mulches, their composition, and also addresses their significance. In addition, we discuss the environmental impact of films, including how it alters the climate, soil, temperature, and weed management.

Differential gas exchange and soil microclimate dynamics under biodegradable plastic, polyethylene, and paper mulches

Biodegradable plastic mulch is potentially a suitable alternative to conventional polyethylene mulch because of the limited disposal options of the latter. However, biodegradable plastic mulch must perform better or comparably to polyethylene mulch to be widely adopted. Gas exchange and soil microclimate are important factors impacted by the use of plastic mulch, which in turn have implications on crop productivity. A controlled-environment study was established in a greenhouse to assess gas exchange and soil microclimate dynamics under biodegradable plastic, polyethylene, and paper mulches with and without planting holes, as well as the impact of the mulches on the growth of sweet corn (Zea mays). A no-mulch condition was included as control. In addition, we monitored CO2 concentrations in the vicinity of planting holes (chimney effect) in a greenhouse and agricultural field conditions under sweet corn production. The plastic mulches (both biodegradable plastic and polyethylene mulches) decreased the soil O2concentration to a minimum of 181–183 mmol mol-1, and when compared to the no-mulch, the plastic mulches reduced water loss within 50 days by 35–68 mm. The paper mulch inhibited light penetration more than did the plastic mulches. There was an increase in the CO2 concentration at 2.5 cm above the planting holes in the plastic mulches compared to that under the no-mulch. However, the differences were not discernible at 15 cm above the ground. Consequently, we did not observe significant impacts on the growth of sweet corn, possibly, because the canopy height of sweet corn was more than 15 cm within a few days after planting. Overall, the plastic mulches did not reduce O2 concentration below 100 mmol mol-1, the minimum level in which plant growth becomes impaired. Also, the often reported improved growth of sweet corn from plastic mulching could be attributable to other factors, such as weed control, reduced water loss, and early season soil warming, rather than elevated CO2 concentrations and fluxes in the vicinity of planting holes. Highlights- Gas exchange and soil microclimate dynamics under biodegradable plastic, polyethylene, and paper mulches were assessed - Elevated CO2 levels were observed near planting holes of plastic mulches (both biodegradable and polyethylene) - The plastic mulches inhibited O2 exchange, but not to a level that could impair plant growth - Polyethylene mulch conserved soil water better than biodegradable plastic and paper mulches - Paper mulch inhibited light penetration better than plastic mulches