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Blanke, M.M. Sustainable Use of Plastics in Horticulture. Encyclopedia. Available online: https://encyclopedia.pub/entry/47942 (accessed on 04 July 2024).
Blanke MM. Sustainable Use of Plastics in Horticulture. Encyclopedia. Available at: https://encyclopedia.pub/entry/47942. Accessed July 04, 2024.
Blanke, Michael M.. "Sustainable Use of Plastics in Horticulture" Encyclopedia, https://encyclopedia.pub/entry/47942 (accessed July 04, 2024).
Blanke, M.M. (2023, August 11). Sustainable Use of Plastics in Horticulture. In Encyclopedia. https://encyclopedia.pub/entry/47942
Blanke, Michael M.. "Sustainable Use of Plastics in Horticulture." Encyclopedia. Web. 11 August, 2023.
Sustainable Use of Plastics in Horticulture
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This entry is adapted from the peer-reviewed paper 10.3390/su151511629

The sustainable use of plastics in horticulture is investigated based on 4 criteria, the three Rs (reduce, reuse, and recycling) plus a re-place strategy, taking into account possible alternatives to plastics. Hail (and insect) nets made of HD-PE, with their long-term use mostly on apple and polytunnels of LD-PE for cherry and strawberry as well as solarisation mulches (reuse), were found to be relatively sustainable solutions for their needs and are currently without alternatives. In contrast, standard black mulch, with its largest share among horticultural plastics, had the widest range of sustainable alternatives, ranging from biodegradable to spray mulch; few sustainable alternatives are available for fleeces and reflective mulches. For the third sustainable option, pilot recycling schemes were examined, such as PolieCoTM (Italy), MAPLATM (Spain), and ERDETM (Germany); they collect 30–50% of the agricultural plastics used in their respective areas, with a successful retrieval growth rate of ca. 20% per year in the case of ERDETM. For the fourth new R option (replace), future sustainability perspectives for the predominant black mulch are research into and development of better, biodegradable, non-fossilbased plastics, sprayable mulch; microbes for the digestion of deployed polyolefins and, for a certain limited range (on shade tolerant crops or in high-light intensity environment), hail nets and polytunnels that are equipped/substituted by/with solar panels (“agri pv”) for the concomitant sustainable production of green renewable energy.

biodegradable mulch climate change consumer demand flower pots hail net PE PLA PP reflective mulch soil moisture conservation

1. Introduction

Why Plastics?

Plastic plays a dominant role in agriculture and horticulture, and it answers the following question [1][2]: “Can horticulture exist and provide year round supply of local fruit by a horticultural process called forcing (from strawberry, cherry to white asparagus), ensure fruit quality, save water and herbicides and protect the crops from insects and climate change (hail)?”.

2. Alternatives (Plastics) to Black Mulch-PE versus PLA

A wide range of papers (e.g., [3][4][5][6][7][8][9][10]) have dealt with alternative biodegradable plastics on bare soil for short cultivation cycles, but they are unsuitable for long-term covers on a rough soil surface. Their main practical and ecological advantages are that they can be left in the field (Figure 1) and/or buried in the soil to be degraded by microorganisms. Fungi, bacteria, and algae can transform these residues into carbon dioxide, methane, water, and biomass [3][6][8].
Sustainability 15 11629 g010 550
Figure 1. Biodegradable alternatives to fossil-based mulch can leave fragmented residues at the end of a crop cycle here in a demonstration plot at the Floriade, Almere (Nl) (© M. Blanke).
The biodegradable mulches currently in use are mainly based on starch and cellulose, polyhydroxybutyrate/valerate copolymers (PHB), and polylactic acid polymers (PLA) (Cozzolino et al.) [9], which are molecules that are susceptible to UV- and visible light-facilitated photo-oxidation or that are thermo-oxidized at high temperatures [3][11][12]. While PLA and PBB are “compostable under industrial conditions and completely degrade in the soil” (EN 13432) [13], PHB so far lacks physical strength for field use, which is an objective for the current research project ENSURE. PLA polylactic/copolyester blends, which is currently the most likely alternative, originate from a corn starch fermentation process. They are chemically synthesized and are hence not of fossil origin. But is PLA more sustainable than LD-PE, e.g., when used as black mulch in strawberry cultivation in Spain or elsewhere?
A limitation of biodegradable films is that, similarly to PE films, they are subjected to weathering and the chemical substances that are used on crops, as well as to soil microorganisms; hence, there is a risk of incomplete soil coverage for the entire crop cycle. Dark or transparent PE mulch used in agriculture fulfill certain criteria [9], such as the tensile strength at break or the tensile elongation at break of at least 16 MPa and 180–250%, respectively. Biodegradable films have both tensile stress and tensile elongation at a break that is lower than those of PE (Scarascia-Mugnozza et al., 2011) [3]. However, their mechanical properties fall within the range required to ensure an adequate soil coverage during the entire strawberry growing cycle. Moreover, on the basis of ecotoxicological tests, the authors demonstrated the absence of soil ecotoxicity at the end of the crop cycle after burying the material. To balance the biodegradation and physical–mechanical properties of a mulch plastic, a biodegradable mulch needs to endure until the end of the crop cycle with adequate weed control, similarly to PE mulch. In Portugal, starch-based biodegradable mulch provided such adequate ground cover and weed suppression during a strawberry autumn–winter cycle (Andrade et al. 2014) [14]. Giordano et al. (2020) [15] favoured three (out of two PEs) (Ecoflex, FKur GmbH, Willich, Germany) and eight PLA (20–40 µm/m2) biodegradable mulches in a strawberry field under the high light/UV/temperature med climate in Huelva, Spain.

2.1. PLA–Biodegradable Plastic (Mulch)—A More Sustainable Option?: “Plough the Plastic”

In practice i.e., the field, a thinner version of PLA (typically 10 µm PLA/m2) compared with PE (30–50 µm) is often used to enable faster biodegradation on and in the soil. This thinner PLA is firstly exposed to light/UV on the ground and then after ploughing to enable intimate contact with soil microbes. Two contrasting independent sustainability studies, both under a comparable Western European climate, exist in the literature. The UMSICHT study (Bertling et al., 2019) [16] is based on modeling, and many assumptions and conclusions severely contrast with the “Imulch” (“intelligent mulch” study 2021) [17]. The study is based on laboratory and sub-commissioned studies and developed new methodologies for applications such as microplastic detection (Table 1).
Table 1. Amount of microplastic (“MP” < 5 mm O) retrieved by two methods, the TED GC-MS and RAMAN spectroscopy analysis after field use (Imulch, 2021) [17].
Land Use PE (30 µm PE/m2) PLA/PBAT (10 µm/m2)
Strawberry <1 µg MP/g <0.1 µg MP/g soil
Asparagus <1 µg MP/g <0.1 µg MP/g soil
Grass meadow <1 µg MP/g <0.1 µg MP/g soil
The 3-year “Imulch” project (2021) [17] showed, contrary to general expectations, a longer longevity of PLA/PBAT films in the field than previously found in the laboratory, where the simulated long-term exposure was speeded up in a short time. While the Bertling study (2019) [16] used 50 µm/m2 PE, the thin 10 µm PLA/PBAT in the “Imulch” study started to biodegrade in Western European fields after 6 weeks but without complete degradation after 3 months the 30 µm PE showed no signs of change.
Table 1 shows that (a) microplastic residues were below detection limits and (b) were independent of the land use, contrary to the expectations and common belief. This is in line with the 2–3% residual LD-PE after field use as assumed (not measured) by Bertling et al. (2019) [16] and which is rated by experts as an overestimate.

2.2. LCA (Life Cycle Assessment) and GHG of Alternative (Biodegradable) Plastics

There are two very different approaches in the literature. In the first one, GHG emissions of ca. 1600 kg CO2e/ha of mulch were similar for both LD-PE (30 µm) and PLA/PBAT (Imulch, 2021) [17] with the energy-expensive precursor adipic acid. The second one (Chen et al., 2023) [18]) also ends up at ca. 1600 kgCO2e/ha for LD-PE, but 2380 kg CO2e/ha for biodegradable PLA/PBAT mulch.
An analysis of the employed LCA shows that it includes nitrite oxide and CO2 emissions during the cultivation phase, but it uses the thinner 10 µm LD-PE mulch. Whereas the first LCA benefits from the thermal digestion of the thicker PE, which is absent from the second study, the latter ends up in a contrary result.

2.3. Hormonal and Endocrinal Activity—Beyond Sustainability

The “Imulch” study (2021) [17] investigated hormone action that was associated with the adsorption of pesticides. The bioassays showed no endocrinal (hormonal) activity of either type of black plastic mulch, no uptake into the plant, and no adsorption and resorption of copper (used as a fungicide in organic growing) or herbicides used in conventional growing.

References

  1. Food and Agriculture Organization. Assessment of Agricultural Plastics and Their Sustainability—A Call for Action; Food and Agriculture Organization: Rome, Italy, 2021; 160p.
  2. UBA. Implementation of Sustainability Citeria—Implementierung von Nachhaltigkeitskriterien für die Sdtoffliche Nutzung; Umweltbundesamt: Berlin, Germany, 2019; Available online: https://www.umweltbundesamt.de/sites/default/files/medien/1410/publikationen/2019-08-19_texte_88-2019_be_biomassenutzung_kunststoffe.pdf (accessed on 10 November 2022).
  3. Scarascia-Mugnozza, G.; Sica, C.; Russo, G. Plastic materials in European agriculture: Actual use and perspectives. J. Agric. Eng. 2012, 42, 15–28.
  4. Hess, P.; Kunz, A.; Blanke, M.M. Innovative Strategies for the Use of Reflective Foils for Fruit Colouration to Reduce Plastic Use in Orchards. Sustainability 2021, 13, 73.
  5. Gür, B.; Kunz, A.; Blanke, M. Reflexionsfolien, Entlaubung oder Biostimulanzien—Methoden zur Intensivierung der Deckfarbe beim Apfel der Sorte ‚Braeburn Hillwell’ im Vergleich. Erwerbs-Obstbau 2023, 64, 1–11.
  6. Peerzada, A.M.; Chauhan, B.S. Thermal Weed Control: History, Mechanisms and Impact. Non-Chemical Weed Control 2018. Available online: https://www.sciencedirect.com/science/article/abs/pii/B9780128098813000024 (accessed on 10 November 2022).
  7. Sander, M. Biodegradation of Polymeric Mulch Films in Agricultural Soils: Concepts, Knowledge Gaps, and Future Research Directions. Environ. Sci. Technol. 2019, 53, 2304–2315.
  8. Kumar, R.; Sadeghi, K.; Jang, J.; Seo, J. Mechanical, chemical, and bio-recycling of biodegradable plastics: A review. Sci. Total Environ. 2023, 882, 163446.
  9. Cozzolino, E.; Giordano, M.; Fiorentino, N.; El-Nakhel, C.; Pannico, A.; Di Mola, I.; Mori, M.; Kyriacou, M.C.; Colla, G.; Rouphael, Y. Appraisal of Biodegradable Mulching Films and Vegetal-Derived Biostimulant Application as Eco-Sustainable Practices for Enhancing Lettuce Crop Performance and Nutritive Value. Agronomy 2020, 10, 427.
  10. Morra, L.; Bilotto, M.; Cerrato, D.; Coppola, R.; Leone, V.; Mignoli, E.; Pasquariello, M.S.; Petriccione, M.; Cozzolino, E. The Mater-Bi® biodegradable film for strawberry (Fragaria × ananassa Duch.) mulching: Effects on fruit yield and quality. Ital. J. Agron. 2016, 11, 203–206.
  11. Briassoulis, D.; Babou, E.; Hiskakis, M.; Scarascia-Mugnozza, G.; Picuno, P.; Guarde, D.; Dejean, C. Review, mapping and analysis of the agricultural plastic waste generation and consolidation in Europe. Waste Manag. Res. 2013, 31, 1262–1278.
  12. Lamont, W.J. Chapter 3—Plastic mulches for the production of vegetable crops. In A Guide to the Manufacture, Performance, and Potential of Plastics in Agriculture; Elsevier: Amsterdam, The Netherlands, 2017.
  13. EN 13432; Packaging. Requirements for Packaging Recoverable through Composting and Biodegradation. Test Scheme and Evaluation Criteria for the Final Acceptance of Packaging. European Standards: Plzen, Czech Republic, 2002.
  14. Andrade, C.S.; Palha, M.D.G.; Duarte, E. Biodegradable mulch films performance for autumn-winter strawberry production. J. Berry Res. 2014, 4, 193–202.
  15. Giordano, M.; Amoroso, C.G.; El-Nakhel, C.; Rouphael, Y.; De Pascale, S.; Cirillo, C. An Appraisal of Biodegradable Mulch Films with Respect to Strawberry Crop Performance and Fruit Quality. Horticulturae 2020, 6, 48.
  16. Bertling, J.; Zimmermann, T. UMSICHT Study by Fraunhofer. 2019. Available online: https://www.umsicht.fraunhofer.de/de/forschung-fuer-den-markt/kunststoffe-in-der-umwelt (accessed on 12 December 2022).
  17. Imulch. IUTA Duisburg—Project Co-Funded by the EU Regional Development Fund EFRE. 2021. Available online: https://renewable-carbon.eu/news/?p=67195 (accessed on 22 November 2022).
  18. Chen, B.; Cui, J.; Dong, W.; Yan, C. Effects of Biodegradable Plastic Film on Carbon Footprint of Crop Production. Agriculture 2023, 13, 816.
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