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# Comparison between natural and synthetic biodegradable mulches: selection criteria and agronomic performance
Challenges in Agriculture
Polyethylene mulches have been present in the agricultural sector for over 60 years. Representing over 35% of the total plastics used, they are the most important class of plastic in the sector. Their use has brought major benefits across most growing areas in the world, with benefits including reduction of early and late frosts, more rapid crop development, higher yields, improved irrigation efficiency, better weed control and shorter times to harvest.
But these plastic mulches are not without adverse effects and have generated significant “plastic pollution” in the long term. Farmers who have used these films must set up a long and expensive recycling circuit for these materials or must remove them after each crop cycle so that they do not leave residues that could block the soil or limit the penetration of water.
Hence two questions arise. Firstly, how can we reduce the number of plastics and, therefore, waste? And secondly, how can we make these plastics more sustainable and, above all, not harmful to our soils? The answer may lie with biodegradable mulches.
This agricultural film allows you to save labour (=reduction of mechanical and manual labour) and helps to guarantee crop yield and quality. As they are produced from biopolymers and
integrate directly into the soil after use, they leave no residue and do not need to be picked up or shipped to an expensive recycling centre.
This article looks at the biodegradable mulches available in Europe to help you understand their inherent features and make the right choice according to your needs and your
expectations.
Thus, let’s start with a current problematic
All plastic mulch materials used in agriculture are currently manufactured from fossil resources, such as natural gas, fuel oil or coal, which will eventually become depleted. In addition, virtually all plastic materials are chemically identical (except for biodegradable plastic), unalterable and their sources are not renewable.
According to Picture 1, plastics made from fossil resources are broken down into two categories: biodegradable and non-biodegradable plastics. Due to their stable polymeric structure, they all persist for many years in nature and cause major waste build-up. However, biodegradable plastics (most commonly used in the agricultural sector) have a biological recirculation pathway that allows them to return to the natural environment.
This diagram summarizes the entire life cycle of the biodegradable plastic.
In the short term, biodegradable products provide many advantages:
– As residues do not accumulate in soil and water, this type of plastic does not harm the environment;
– Complete disposal of the material during composting;
– The use of biodegradable material does not require a return system or separate waste collection, thus saving time and money.
So today, in order to bring together many different definitions in the agricultural world, a biodegradable material is synonymous with:
While biodegradable plastics can be biodigested, biocomposted or incinerated, they should not be confused with common plastics. In fact, while being used, they help to reduce the environmental load of waste and improve the disposal composition, since they are less dependent on limited fossil resources.
In this sense, biopolymers (Picture 2) such as polycaprolactone (P.C.L), polylactic acid (P.L.A.), starch, pectin, cellulose, collagen and polysaccharides can be reliable alternatives in the production of a biodegradable polymer mulch plastic film. Therefore, the use of this type of biodegradable agricultural plastic film allows the reduction of waste management costs and benefits the environment directly and indirectly by eliminating the need for incineration and reducing the use of fossil resources. Biodegradable materials close the natural carbon n cycle and ensure a constant CO2 fixation in the plant material.
Choice of non-biodegradable polymers
Unlike non-biodegradable plastics, agricultural plastics (buckets, tubes, pipes, strings, twines, ties, nets, sacks, containers, bottles, nurseries, pots, backpacks, fabrics, covers and films), which are mainly made of polyethylene, polypropylene and poly (ethylene vinyl acetate), are transformed into x ualuable products incineration, recycling and reuse.
However, recycling and reuse of agricultural plastics is limited because these materials are easily contaminated with organic and inorganic agents, such as fertilizers, pesticides and soil, which are difficult to remove and may compromise the subsequent use of recycled or reprocessed products. Furthermore, incineration is not a complete solution because all agricultural plastics are burnt at high temperatures and this process is often very expensive. In addition, incineration of agricultural plastics generates carbon dioxide, a greenhouse gas that contributes to global warming, and other harmful by-products such as hydrochloric acid fumes, carbon monoxide and other potentially toxic gases that may generate environmental safety problems.
Nowadays, much attention is paid to the development of biodegradable agricultural plastic materials by incorporating alternative biodegradable polymers and pro-oxidant chemical groups into PE.
Agricultural biodegradable polymers, films and sheets
Many countries are now testing biodegradable films made from starch, cellulose acetate (CA), polycaprolactone (PCL), poly (vinyl alcohol) (PVOH and PVAL), polyethylene terephthalate (PT), aliphatic polyester, copolyester and polylactic acid (PLA).
PCL and other biodegradable polymers have been used to develop greenhouse aprons, which have the good biodegradability and can be mixed with several organic compounds in compost.
In addition to the PCL mulch film, agriculturists also use slow-release film for fertilization and film coated with herbicides or pesticides. Indeed, planning certain active or useful agents on a biodegradable polymer such as PCL can increase the efficiency of these films and lead to lower consumption, different formulations, controlled distribution of chemicals, fewer environmental hazards and lower toxicity in the atmosphere.
To address the shortcomings of biodegradable plastics and their composites on the nutritional input of the plant, starch-filled plastics are currently being developed. In combination with fertilizers, soil conditioners and other mixtures, starch-filled plastics are more effective in their respective applications. In addition, these plastics require less mechanical labour than the use of conventional fertilizers for agricultural applications or soil conditioning. For these reasons, starch-filled agricultural plastics could be adopted by many farmers.
PCL can be treated to provide optimal properties and is increasingly being used as a raw material, rather than waste from fossil fuels. Tailoring the properties of PCL for a certain
application is a useful and innovative strategy, for example starch-filled PCL mulch films, which have a shorter period of biodegradation in the soil, due to the starch content, and are stable in application, due to the PCL phase and its processability.
Biodegradable polylactic acid (PLA) is a polymer derived from starch that serves in particular as a container for plant or tree seedlings, and has demonstrated its efficiency as d agricultural plastic film.
To transfer from the fields of plastic, what is PLA?
PLA (polylactic acid or polylactide acid) is a thermoplastic biosourced aliphatic polyester derived from biodegradable renewable resources, such as corn starch (in the United States and Canada), cassava, potatoes, sugar beet pulp or sugar cane (elsewhere in the world) and from biodegradable waste such as beet pulp or sugar cane…
PLA has similar properties to other polymers such as polypropylene (PP), polyethylene (PE) or polystyrene (PS). PLA is the second most produced bioplastic (after thermoplastic starch) and has similar properties to polypropylene (PP), polyethylene (PE) or polystyrene (PS), as well as being biodegradable and suitable for cotton and biopolymer fibers using a 3D film printing process.
Today, PLA has the largest share of global bioplastics production, with an annual production capacity of approximately 300,000 tons. There are several commercial forms of PLA. For example, NatureWorks of Minnetonka (Minnesota) is the largest producer of PLA (biopolymer) in the world, with a capacity of 150,000 tons per year, under the brand name Ingeo™. In this formulation, the lactic acid is derived from plant starch (100% natural). It is therefore important to distinguish this polylactic acid (PLA) from polylactic acid, which is derived from lactic acid molecules of petrochemical origin. Finally, compared to polylactic acid (L-PLA), polylactic acid (D-PLA) has better processability and hydrolysis resistance. It is a copolymer used in the pharmaceutical industry because of its slower biodegradability.
End of life and Environment
PLA can be obtained by fermentation or chemical synthesis but two cleaning processes are possible for this plastic: mechanical composting (the plastic is degraded by microorganisms and chemicals such as bacteria) and chemical composting (the plastic is chemically broken down and the compounds are then used again in the plastic production process).
PLA is considered a clean plastic because it does not emit any toxic gases such as nitrides or sulfides when incinerated. The environmental impact of producing PLA (with no BPA or P. V.C) makes it a biodegradable plastic best suited for commercial applications such as plastic films and bottles and biodegradable medical devices (e.g. pins, rods, screws and plates). Thus, because PLA is more similar to our own body polysaccharides than conventional hydrocarbon based plastics, it is perfectly safe for use in these medical fields and has completely renewable raw materials. PLA is not only used in human medicine, but it can also be used in veterinary medicine for implants. After a period of time, the material is degraded by the body without the need for removal. Currently, the use of PLA in self-healing implants and in the medical field has been a success, but it is the agricultural sector that PLA has attracted the most attention…
Many countries are now testing biodegradable films made from starch, cellulose acetate (CA), polycaprolactone (PCL), poly (vinyl alcohol) (PVOH and PVAL), polyethylene terephthalate (PT), aliphatic polyester, copolyester and polylactic acid (PLA).
It’s totally natural!
The use of bagasse, or more recently distillery residues from the alcohol industry, demonstrated that sugar cane can out-compete starch as the cheapest raw material for PLA production. But the commercial producer NatureWorks LLC (Cargill) now derives an increasing proportion of its lactic acid from the fermentation of corn dextrose.
Derived from biodegradable renewable resources, PLA can be used in a wide range of food packaging to create a closed loop of life as it then moves through the compost heaps back to the soil, where corn or sugarcane is again grown to produce more PLA.
This recyclable plastic can degrade into lactic acid (monomer) and decompose into CO2 and H2O. The monomer is non-toxic, so PLA is biodegradable and environmentally friendly.
Focusing on these properties, a large number of biodegradable products developed in recent decades contain PLA. Thus, from an environmental point of view, this polymer can compete with traditional polyester. But attention, PLA takes a long time to fully degrade (from 6 months to 2 years after processing and sterilization). So avoid incineration at lower temperatures.
In addition, PLA can be used in the packaging, textile and medical industries, replacing polypropylene (PP) and polyethylene terephthalate (PET).
Are biodegradable plastics really sustainable?
Today, more and more Europeans are using biodegradable plastic products to save resources, dispose of plastic waste and reduce their environmental impact. But these products do not decompose immediately and require special disposal conditions. When incinerated at low temperatures, biodegradable plastic materials release pollutants. For more information, read: “European Environment Agency / Ilmo van Breda / EEA. “.
They are often unable to compost under natural disposal conditions.
For example, an experiment conducted with compostable plastic bags made of cornstarch, PLA and PBAT showed that the bags did not degrade after 27 months either in the sea or in the soil, while the bags exposed to air degraded into pieces after nine months.
When incinerated at low temperatures, biodegradable plastic materials can release pollutants. Advanced thermal treatment with thermal oxidation of pollutants provides much better environmental performance avoiding toxic pollutants.
While biodegradability may be generally desirable, materials that biodegrade quickly, such as cellulose, are often not durable because they break down when dehydrated, suddenly heated, exposed to sunlight, or hit by higher frequency energy (ultraviolet). Paradoxically, biopolymers are not very stable.
Therefore, society needs materials that are stable but can degrade quickly once discarded (dump sites or accidental waste) under ambient conditions without special treatment. A universal method for achieving this is not yet known.
Because of the high molecular weight of plastics and their low surface-to-volume ratio on solid surfaces, physical compatibility with polymer-degrading enzymes and effective accessibility to neighboring enzymes are very limited compared to the biodegradation of low molecular weight compounds.
Essential properties of their administrations can provide more effective access to polymers and facilitate rapid biodegradation to normal biodegradation conditions.
As a result, new methods for making biopolymers and plastics new methods are constantly being sought, along with means of properly disposing of the plastic products we now use more and more regularly in our societies. Europe is very sensitive to the recycling of bioplastic wastes. The directive for plastic waste recycling recognizes that, for Europe, the recycling of plastic waste can be a promising waste management method within its policy of non-toxic environment and circular economy. As an example, the collaboration between the small wind turbine manufacturer EOLFI and the recycling company SUEZ points to a similar issue…
But this will not be enough.
Indeed, many scientists suspect that much of the millions of tons of waste of these plastics end up in illegal landfills, in nature and in the ocean, but, once abandoned, they become resistant to bacteria and pollution and pollution by micro-plastics, as if they were not degradable…
The biodegradable plastics that are currently being developed do not appear to offer an effective solution to this problem of plastic pollution…
Comparison of biodegradable and non-biodegradable agricultural films
To understand better, an experiment was conducted to compare non-biodegradable agricultural films (PE, PP or PVC) with biodegradable agricultural films (PCL, ECP and Cello film) in a greenhouse environment. In this study, the heat absorption rate of three PCL-based biodegradable films was lower than that of the PE film initially, as the rate increased significantly after six months of weathering.
The loss of heat absorption capacity is attributed to the breakage of the polymer structure of PE. These breaks are caused by sunlight and ultraviolet light, which cause physical changes in the material due to macromolecular cracking. Since the biodegradable films are based on PCL, they did not show obvious cracks or macroscopic defects. Therefore, even after six months, the chemical structure of the biodegradable films remained unharmed.
Гнатоль topлупенцья грамофоторенлий тобоплевен пос зберниках, валантоплю неторин, новреми фабритуйатолий петецомбия поминтамия петелия фалий млин радепандарйат.
The results show that the biodegradable films studied were able to absorb light energy before aging, becoming almost transparent with a very weak blue color. This is the result of the elimination of the color in the PCL film formulation. This feature was already considered in 1995 by the developers of the film. For this purpose, they modified the P.L.A film or extracted its color. However, from a practical point of view, we need to insert a color into the biodegradable films during their production, as it has become common practice for agriculturists. The weak blue colour in the PCL film almost disappears after six months of exposure to the natural environment.
The color of the polyethylene coating film remains more or less constant during the same period.
Из биополимие фабриканты пронцыулю Химической Фотодрорреции устранить петелиндурмят, который cкрывается, что комментировать не гнатным обмоиному в передавывательным радутации. This is because, as mentioned earlier, most biopolymers and biodegradable plastics require specific degradation conditions, such as special water harvesting plants with high inorganic nitrogen levels, their hydrophobicity and the low pH after several years of use. To reduce soil erosion, biodegradable films must therefore be removed from the soil after use and not embedded in it. As such, agricultural films could be reused as soil additives in the fields.
In other words, agricultural films should be made in such a way that they can be easily removed and are suitable for reuse as soil improvers. Another possible solution is to use a material that is neither removed nor utilized after use, but which can be mostly embedded in the soil of the crop field, since this does not inhibit root growth or degrade crop quality or quantity.
Nevertheless, these plastics are not biodegradable. They are difficult to remove from fields, as they can block crop growth and water penetration into soil, a process known as “crop downsizing”. Because biodegradable polymers and plastics can become part of the soil after their use, there is no need for mechanical or chemical processing. In addition, the manufacturing process is “clean”, which is not the case for the manufacture of traditional polymers such as PE, PP or PVC. Indeed, the recent development of biodegradable polymers such as PCL, starch blends and aliphatic copolyesters has opened up new applications for these materials, especially as biodegradable films for outdoor agriculture and as biodegradable greenhouse liners. Natural polymers such as starch, pectin, cellulose and proteins have all been used to develop excellent materials for gardening by scattering soil, inside or on top of agricultural land.
Thus we can ask ourselves: Which film to choose?
In terms of cost: Non biodegradable PE
in terms of Performance: Non biodegradable PE
in terms of environmental impact: Biodegradable films are clearly the winners.
As we have seen, films made from biopolymers and biodegradable plastics represent a greater environmental benefit than non-degradable polymeric agricultural films.
Economiческая поеды: Whether with PE or with a biodegradable film, the economic profitability of the crop is guaranteed once market prices have been reached. Indeed, to the farmer, the vegetable price alone has a justification and an economic interest, regardless of other elements, such as the price of the film.
Peакция: Farmers have encountered serious problems with the use of the material, mainly due to lack of experience. After experimentation by the farmers and discussion, they have understood that biodegradable films are simply “less resistant” than normal films and that they will therefore have to adapt their cultivation practices.
Практика: The conclusions of this study (Picture 4) allow to compare the biological, commercial and financial performance of PE and biodegradable films.Overall, it seems that the dissuasive effect on the economic profitability of crops appears to be marginal. It confirms the conclusions of previous Voortmont studies on potatoes or on asparagus: once market prices have been reached, economic profitability, both with PE and a biodegradable film, is ensured. The reasons for the high profitability per hectare are: weather conditions in early 2017 and market prices of asparagus in 2017.I ouis的情況:
Production methods: Sustainable production in the sense of environmentally friendly, such as natural energy supply and organic cultivation. Still, in the spring of 1976, the Institute for Agricultural Technology (ITAP) in Kimloch, Germany, applied for, and was granted, a patent for the invention of “soft topsoil paper”.
At the end of the 20th century, the practice of covering soil with synthetic plastic sheeting along seed rows or plant rows using hydrocarbon polyvinyl chloride (PVC) resin was introduced. By blocking light and air, straw eliminates all weeds, retains the blood moisture needed for sprouting seeds, minimizes water loss for a period of time (20-30 days), retains nutrients and promotes healthy germination, or healthy plant pollination. However, as we mentioned above, it is clear that the use of plastic film as mulch covering will cause “white pollution” and other negative effects on the biological and agricultural environment.
In addition, this film is not easily degradable or recyclable, which affects the sustainable ecological development of agro-ecosystems. It has no strength and is easy to break. More recently, the European Union Regulations no. 2092/91 and no. 834/2007 prohibit the use of mulch for agricultural organic production. However, non-woven paper, regardless of fiber type, must be 100% recyclable. Pieces can be easily mixed into the soil, where they are decomposed by microorganisms. At the end of the season, the bioplastics from which the films are made (100% oxo bio-degradable – Picture 5) are deposited in the soil, where they degrade naturally, without leaving heavy metals in the soil.
The use of paper (straw) was officially approved in the above regulations. It was not until 2016 that a soft-top paper mulching technology was developed in the province of Shangtung, in northeast China, for all crops (including rice). Three layers of paper can be applied one above the other, i.e. from 30 to 60 g/m2. The first two layers must be temporarily unrolled in the field in order to form them and adapt them to the soil. This technique helps to reduce the incidence and severity of tomato diseases compared to the unmanaged control, thus making it a viable option for organic and non-organic producers. As a result of its use, one can expect better disease control than with straw mulching or bare soil management. Regarding the porosity of the paper, as it covers the soil surface, interfering with the exchange of water, minerals, carbon dioxide and oxygen between the soil itself and the surrounding atmosphere, shading the soil, the intensity of the sunlight on the soil is changing and the temperature on the soil surface is significantly decreasing. Then the cellulose in the paper is degraded by soil microorganisms into amino acids, sugars and organic acids, which are both simple compounds for plants to absorb (a good example of plant growth biostimulation – see AGRIAPP) and microorganisms for production. In any case, the use of this paper made from wheat straw allows the transition from grain production to a circular, sustainable and profitable economy.
Building on this initial observation, the let
’The European Union has implemented an innovative idea and created specific tools to improve and accelerate the rate of biodegradable paper digestion, creating a database that compares different forms of biodegradable paper digestion according to its chemical composition as well as different types of film mulching. Embryonic research shows that the management of paper mulches (Picture 6) is more efficient than straw mulches or even bare soil for organic farmers.
Thus, from such reports, it is clear that the use of paper mulching can not only eliminate soil contamination, decrease penetration of the surface below the plastic film, which also improves the surface water content and facilitates the growth of active microorganisms. Ultimately, the higher temperature in the applied film mulching affects the growth of suspended aquatic microorganisms, which can degrade plants, the behavior of forest plots or the composition of soil ecosystems.
Barbier notes that LCO3, the modified form of paper mulching, produced high-quality tomatoes, i.e. large, with a high ratio of sugar to titratable acidity and a low incidence of insect damage, compared to straw and bare soil mulch. In addition, compared to 100% paper mulch management, tomato fruits taken from plants are damaged less frequently by certain types of worms (Helicoverpa Zea (Boddie) and Spodoptera exigua (bollworm)).
Indeed, most aphids land on weeds before moving to tomato plants and cause damage, and this latter type contains crystals that sid upports directly to their whitefly pests (Sida acuta burm), so paper films do not serve as refuge for common pests. These potential benefits of paper mulch underline its disadvantage due to strong group competition or weed reduction.
Several studies demonstrate the benefits of suppressing weeds with paper mulch for tomato management. Due to their ability to bury weeds in the soil and their decomposition into simple compounds, the worms (Eisenia nordenskioldi and Metaphire Guillelmi) that break up organic matter and form worm castings in such mulch are an essential part of the agricultural food chain. In fact, worms eat 90% of organic matter and 10% mineral soil by weight, and are responsible for converting a large fraction of organic matter into reusable clean worm production networks (humic and fulvic products – see LEBOSOL).
To confirm the effectiveness of this practice, a study was conducted at the University of Stanislaus to determine the most effective paper management available for organic systems to test quality and quantity of tomato fruits essentially from “field and slope to consumer”.
Conclusion
However, it appears that polyethylene film residues do exist after removal, but, fortunately, this does not cause health or crop quality problems and are not affected by soil pollution. The impact caused by the residues of this film showed that they could be maintained along a certain length of film (between 1 and 101 film strips or 3 and 303 cm film per unit length).
Previous reviews of biodegradable paper told us that the utilization of various crop wastes, such as rice husk, straw, sawdust, town waste, fly ash, alcohol waste, oyster shell charcoal powder, charcoal waste and coastal sediment forest, which seem to get rid of their useless elements by exposing them to high temperatures obviously improves the nature of the soil.
Even if it is difficult to transform the paper into reusable plants (biostimulation and biocontrol) after suitable fermentation, the preparation can be enriched by fertilizers, nutrients and various other elements (biochar or oligo-elements) for proportional insertion and introduction as a basic paper for raising seedlings. Despite the fact that soft cover mulch paper consists of [a] newspaper substrate layer containing cellulose, hemicellulose, lignin, etc. This is often required and used by crop farmers.
These paper coatings can be organic, based on biological substances such as paper, worms, compost… and inorganic (coal, fly ash, alcohol processing waste). However, in modern agriculture, synthetic films based on polypropylene and polyethylene are the main source of plastic mulch, which causes serious environmental damage.
It has become clear that the use of synthetic films based on unicellular organisms and their own groups of bacteria, or low molecular weight bacterial populations based on natural paper coatings, should create a healthy solution for green soil. A.T. Lebosol, [G] Bozkurt, [O] Pacs, [F]
Kader, Pashakolaee, [M] Items, [B] Zagan, [A] So, [G] Soil Proxies (2019), [P] Lanna Garbage Paper (2019) ”Field issgsg.g brick of Qlriot ## Authors ## Authors # Comment P
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