Biodegradable plastic mulch was introduced in the 1990s as an alternative to PE mulch, which has been used in agriculture worldwide since the early 1960s to control weeds, conserve soil moisture, modify soil temperature, shorten time to harvest, and increase crop yield and quality (Kasirajan and Ngouajio, 2012; Kyrikou and Briassoulis, 2007; Miles et al., 2012; Sarnacke and Wildes, 2008). Plastic mulch is more flexible, easier to apply mechanically, and less expensive than natural mulches (e.g., straw, woodchips). However, PE mulch removal and disposal can be costly (Galinato et al., 2012; Galinato and Walters, 2012; Ghimire and Miles, 2016), and there are only a handful of agricultural plastic recyclers that will accept PE mulch due to the large amount of soil contamination (up to 70% by weight). It is estimated that less than 10% of agricultural PE mulch generated in the United States is currently recycled, with the majority being landfilled or burned in the field at the end of the growing season (G. Jones, personal communication; Grossman, 2015; Levitan and Barros, 2003). Although PE mulch recycling is well established in central Europe, in many other regions of the world, PE mulch is tilled into the field or is dumped in adjacent areas, creating a significant waste issue (Liu et al., 2014; PlasticsEurope, 2015; Scarascia-Mugnozza et al., 2011).
Biodegradable plastic mulch that performs similar to PE mulch during the cropping season and can be tilled into the field at the end of the season without compromising soil quality or the environment could be an asset for sustainable agriculture. It is worth noting that if biodegradable mulch enters the plastic recycling stream it will contaminate the recycled feedstock, resulting in unusable end product; thus, on-site disposal of biodegradable mulch is most desirable. Although there are several plastic mulch products on the market that are advertised as biodegradable, none of these have been evaluated in long-term studies to determine the rate and extent of biodegradation under agricultural field conditions. Until research addresses this information gap, growers and agricultural professionals must rely on information regarding the constituents of mulch as well as feedback provided by mulch manufactures to anticipate how the mulch will biodegrade in fields after soil incorporation.
Organic and sustainable growers are particularly interested in the opportunity to use a biodegradable plastic mulch (Goldberger et al., 2015). PE mulch has long been allowed for use in organic crop production [U.S. Department of Agriculture (USDA), 2014a]; however, it was only on 30 Oct. 2014 that the USDA NOP passed a final rule that added biodegradable biobased plastic mulch to their list of allowed synthetic substances [7 Code of Federal Regulations (CFR), Section 205.601; USDA, 2014b]. Before this, the only synthetic biodegradable mulch allowed in certified organic production was paper mulch. On 22 Jan. 2015, the NOP clarified that the polymer feedstocks used to make biodegradable mulch must be completely biobased (USDA, 2015). According to the new rule, the primary requirements for a mulch to be considered biodegradable and biobased are that a mulch film must:
Reach at least 90% biodegradation in the soil within 2 years or less as evaluated using standardized tests such as International Organization for Standardization (ISO) 17556 or ASTM International D5988.
Fulfill criteria for being biobased as evaluated using standardized tests such as ASTM D6866.
Meet compostability specifications of either ASTM D6400, ASTM D6868, European Standards (EN) 13432, EN 14995, or ISO 17088 (7 CFR, Section 205.2).
Be produced without organisms or feedstock derived from excluded methods [7 CFR, Section 205.601(b)(2)(iii)].
The objective of this paper is to broaden the understanding of biodegradable plastic mulch and its potential suitability for organic and sustainable cropping systems. The definition of “biobased” is reviewed along with the composition, manufacturing methods, and use of minor additives in biodegradable mulches. Further, biodegradation of common mulch feedstocks in general, and expected in-soil biodegradation potential in particular, are discussed, along with potential for accumulation of mulch residuals in the soil after repeated applications. Although the focus is on certified organic systems, how biodegradable mulches may complement or detract from the sustainability of conventional and other alternative production systems is also addressed.
American Society for Testing and Materials (ASTM) 2012 Standard test methods for determining the biobased content of solid, liquid, and gaseous samples using radiocarbon analysis. ASTM D 6866-12. ASTM International, West Conshohocken, PA
Bomgardner, M.M. 2014 Biobased polymers: Corporate ingenuity and determination is starting to pay off, but products must still be muscled into the supply chain Chem. Eng. News 92 10 14
Brodhagen, M., Peyron, M., Miles, C. & Inglis, D.A. 2015 Biodegradable plastic agricultural mulches and key features of microbial degradation Appl. Microbiol. Biotechnol. 99 1039 1056
Clerici, M.T.P.S. 2012 Physical and/or chemical modifications of starch by thermoplastic extrusion, p. 39–52. In: A. El-Sonbati (ed.). Thermoplastic elastomers. InTech, Rijeka, Croatia
Cowan, J.S., Inglis, D.A. & Miles, C. 2013 Deterioration of three potentially biodegradable plastic mulches before and after soil incorporation in a broccoli field production system in northwestern Washington HortTechnology 23 849 858
Davis, G., Harrison, D., Bulson, H. & Billett, E. 2005 An evaluation of degradable polyethylene (PE) sacks in open windrow composting Compost Sci. Util. 13 50 59
Eubeler, J.P., Zok, S., Bernhard, M. & Knepper, T.P. 2009 Environmental biodegradation of synthetic polymers I. Test methodologies and procedures TrAC, Trends Analyt. Chem. 28 1057 1072
Feuilloley, P., César, G., Benguigui, L., Grohens, Y., Pillin, I., Bewa, H. & Jamal, M. 2005 Degradation of polyethylene designed for agricultural purposes J. Polym. Environ. 13 349 355
Galinato, S.P., Miles, C. & Ponnaluru, S. 2012 Cost estimates of producing fresh market field-grown tomato in western Washington. Washington State Univ. Ext. Publ. FS080E
Galinato, S.P. & Walters, T.W. 2012 Cost estimates of producing strawberries in a high tunnel in western Washington. Washington State Univ. Ext. Publ. FS093E
Ghanbarzadeh, B. & Almasi, H. 2013 Biodegradable polymers, p. 141–185. In: R. Chamy and F. Rosenkranz (eds.). Biodegradation: Life of science. InTech, Rijeka, Croatia
Ghimire, S. & Miles, C. 2016 Dimensions and costs of polyethylene, paper and biodegradable plastic mulch. Washington State Univ. Ext. Factsheet. 16 June 2016. <http://vegetables.wsu.edu/AltMulch.html>
Gilmore, D.F., Antoun, S., Lenz, R.W. & Fuller, R.C. 1993 Degradation of poly(hydroxyalkanoates) and polyolefin blends in a municipal wastewater treatment facility J. Environ. Polym. Degrad. 1 269 274
Goldberger, J.R., Jones, R.E., Miles, C.A., Wallace, R.W. & Inglis, D.A. 2015 Barriers and bridges to the adoption of biodegradable plastic mulches for US specialty crop production Renew. Agr. Food Syst. 30 143 153
Grossman, E. 2015 How can agriculture solve its $5.87 billion plastic problem? GreenBiz. 20 June 2016. <https://www.greenbiz.com/article/how-can-agriculture-solve-its-1-billion-plastic-problem>
Hablot, E., Dharmalingam, S., Hayes, D.G., Wadsworth, L.C., Blazy, C. & Narayan, R. 2014 Effect of simulated weathering on physicochemical properties and inherent biodegradation of PLA/PHA nonwoven mulches J. Polym. Environ. 22 417 429
Hayes, D., Dharmalingam, S., Wadsworth, L., Leonas, K., Miles, C. & Inglis, D. 2012 Biodegradable agricultural mulches derived from biopolymers, p. 201–222. In: K. Khemani and C. Scholz (eds.). Degradable polymers and materials: Principles and practice. 2nd ed. ACS Symposium Series, Vol. 1114. Oxford Univ. Press, Washington, DC
Hickey, W.J. 2005 Microbiology and biochemistry of xenobiotic compound degradation, p. 447–466. In: D.M. Sylvia, J.J. Fuhrmann, P.G. Hartel, and D.A. Zuberer (eds.). Principles and applications of soil microbiology. 2nd ed. Prentice Hall, Upper Saddle River, NJ
Ho, K.G., Pometto, A.L. III & Hinz, P.N. 1999 Effects of temperature and relative humidity on polylactic acid plastic degradation J. Polym. Environ. 7 83 92
Jamshidian, M., Tehrany, A., Imran, M., Jacquot, M. & Desobry, S. 2010 Poly-lactic acid: Production, applications, nanocomposites, and release studies Compr. Rev. Food Sci. Food Saf. 9 552 571
Kasirajan, S. & Ngouajio, M. 2012 Polyethylene and biodegradable mulches for agricultural applications: A review Agron. Sustain. Dev. 32 501 529
Khemani, K. & Scholz, C. 2012 Degradable polymers and materials: Principles and practice. 2nd ed. ACS Symposium Series, Vol. 1114. Oxford Univ. Press, Washington, DC
Kijchavengkul, T., Auras, R., Rubino, M., Ngouajio, M. & Fernandez, R.T. 2008 Assessment of aliphatic-aromatic copolyester biodegradable mulch films. Part II: Laboratory simulated conditions Chemosphere 71 1607 1616
Kim, D.Y., Kim, H.W., Chung, M.G. & Rhee, Y.H. 2007 Biosynthesis, modification, and biodegradation of bacterial medium-chain-length polyhydroxyalkanoates J. Microbiol. 45 87 97
Krzan, A., Hemjinda, S., Miertus, S., Corti, A. & Chiellini, E. 2006 Standardization and certification in the area of environmentally degradable plastics Polym. Degrad. Stabil. 91 2819 2833
Levitan, L. & Barros, A. 2003 Recycling agricultural plastics in New York State. Environmental Risk Analysis Program. Cornell Univ. 19 Mar. 2016. <http://cwmi.css.cornell.edu/recyclingagplastics.pdf>
Li, C., Moore-Kucera, J., Miles, C., Leonas, K., Lee, J., Corbin, A. & Inglis, D. 2014 Degradation of potentially biodegradable plastic mulch films at three diverse U.S. locations Agroecol. Sustain. Food 38 861 889
Liu, E.K., He, H.Q. & Yan, C.R. 2014 ‘White revolution’ to ‘white pollution’: agricultural plastic film mulch in China Environ. Res. Lett. 9 091001
Lucas, N., Bienaime, C., Belloy, C., Queneudec, M., Silvestre, F. & Nava-Saucedo, J.E. 2008 Polymer biodegradation: Mechanisms and estimation techniques: A review Chemosphere 73 429 442
Maier, R.M., Pepper, I.L. & Gerba, G.P. 2009 Environmental microbiology. Elsevier Academic Press, Burlington, MA
Miles, C., Wallace, R., Wszelaki, A., Martin, J., Cowan, J., Walters, T. & Inglis, D. 2012 Deterioration of potentially biodegradable alternatives to black plastic mulch in three tomato production regions HortScience 47 1270 1277
Organic Materials Review Institute (OMRI) 2015 Report on biodegradable biobased mulch films. U.S. Dept. Agr., National Organic Program, Organic Materials Review Institute, Washington, DC
PlasticsEurope 2015 Plastics: The facts 2014/2015: An analysis of European plastics production, demand and waste data. PlasticsEurope, Wemmel, Belgium
Rasband, W.S. 1997 ImageJ. U.S. Natl. Inst. Health, Bethesda, MD. 17 Sept. 2013. <http://rsb.info.nih.gov/ij>
Reemmer, J. 2009 Advances in the synthesis and extraction of biodegradable poly-hydroxyalkanoates in plant systems. MMG 445 Basic Biotechnol. 5:44–49
Sarnacke, P. & Wildes, S. 2008 Disposable bioplastics-consumer disposables-agricultural films. United Soybean Board, Omni Tech International, Ltd., Midland, MI
Scarascia-Mugnozza, G., Sica, C. & Russo, G. 2011 Plastic materials in European agriculture: Actual use and perspectives J. Agr. Eng. 42 15 28
Shanks, R. & Kong, I. 2012 Thermoplastic starch, p. 96–116. In: A.Z. El-Sonbati (ed.). Thermoplastic elastomers. InTech, Rijeka, Croatia
Thomas, N., Clarke, J., McLauchlin, A. & Patrick, S. 2010 Assessing the environmental impacts of oxo-degradable plastics across their life cycle. Department for Environment, Food and Rural Affairs, London, UK
U.S. Department of Agriculture 2013 Can GMOs be used in organic products? U.S. Dept. Agr., Washington, DC. 7 June 2016. <https://www.ams.usda.gov/publications/content/can-gmos-be-used-organic-products>
U.S. Department of Agriculture 2014a National organic standards (NOS) § 205.601(b)(2)(i-ii) synthetic substances allowed for use in organic crop production. U.S. Dept. Agr., Washington, DC. 7 June 2016. <https://www.nofany.org/files/NOP_Organic_Regulations.10.26.15.pdf>
U.S. Department of Agriculture 2014b The national list of allowed and prohibited substances. U.S. Dept. Agr., Washington, DC. 7 June 2016. <http://www.ecfr.gov/cgi-bin/text-idx?c=ecfr&SID=9874504b6f1025eb0e6b67cadf9d3b40&rgn=div6&view=text&node=7:126.96.36.199.32.7&idno=7#sg7.3.205.g.sg0>
U.S. Department of Agriculture 2014c National organic standards (NOS) §205.206 crop pest, weed, and disease management practice standard. U.S. Dept. Agr., Washington, DC. 7 June 2016. <https://www.nofany.org/files/NOP_Organic_Regulations.10.26.15.pdf>
U.S. Department of Agriculture 2015 Memorandum to the national organic standards board, 22 Jan. 2015. National Organic Program. U.S. Dept. Agr., Washington, DC. 7 July 2016. <https://www.ams.usda.gov/sites/default/files/media/NOP-PM-15-1-BiodegradableMulch.pdf>
Van Soest, J.J.G., Benes, K. & Wit, D.D. 1995 The influence of acid hydrolysis of potato starch on the stress-strain properties of thermoplastic starch Starke 47 429 434
Wortman, S.E., Kadoma, I. & Crandall, M.D. 2015 Assessing the potential for spunbond, nonwoven biodegradable fabric as mulches for tomato and bell pepper crops Scientia Hort. 193 209 217
Wortman, S.E., Kadoma, I. & Crandall, M.D. 2016 Biodegradable plastic and fabric mulch performance in field and high tunnel cucumber production HortTechnology 26 148 155