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Biodegradable Plastic Mulch and Suitability for Sustainable and Organic Agriculture

Biodegradable Plastic Mulch and Suitability for Sustainable and Organic Agriculture

FS103E
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Shuresh Ghimire, PhD Candidate, Department of Horticulture, WSU Mount Vernon Northwestern Washington Research and Extension Center, Doug Hayes, Professor, Department of Biosystems Engineering and Soil Science, University of Tennessee-Knoxville, Jeremy Cowan, Assistant Professor and Regional Horticulture Specialist, WSU Spokane County Extension, Debra Inglis, Professor, Department of Plant Pathology, WSU Mount Vernon Northwestern Washington Research and Extension Center, Lisa DeVetter, Assistant Professor and Small Fruit Specialist, Department of Horticulture, WSU Mount Vernon Northwestern Washington Research and Extension Center, Carol Miles, Professor and Vegetable Specialist, Department of Horticulture, WSU Mount Vernon Northwestern Washington Research and Extension Center
Polyethylene mulch is environmentally harmful and expensive to dispose of: discover biodegradable plastic mulch as a viable alternative.
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Biodegradable plastic mulch (abbreviated as plastic BDM hereafter) offers crop production benefits similar to polyethylene (PE) mulch but is designed to be tilled into the soil after use thereby eliminating waste and disposal challenges. This publication explains the use of plastic mulch in agriculture, what plastic BDMs are made from, and what constitutes biodegradability. It also provides information about the suitability of plastic BDM for organic agriculture. A glossary of terms associated with the topic is included at the end of this publication.

The use of plastic mulch in agriculture

PE mulch is used for crop production worldwide because it helps to control weeds, conserve soil moisture, increase soil temperature, and increase crop yield and crop quality compared to growing plants on bare ground (Kasirajan and Ngouajio 2012). PE mulch is also readily available at a relatively low cost (Ghimire and Miles 2016). Despite these benefits, the sustainability of crop production using PE mulch has been called into question since PE mulch is not biodegradable and not readily recyclable. Many plastic recyclers will not accept PE mulch because it is contaminated with soil and crop debris (up to 50% by weight) after use (Kasirajan and Ngouajio 2012). Further, there are few plastic mulch recycling facilities in the U.S., so less than 10% of PE mulch is currently recycled (Miles et al. 2017).

The projected use of plastic mulch in North America is estimated to be about 117,700 tons in 2017; most used mulch will be disposed in landfills, stockpiled, or burned on farms (Figure 1) (MarketsandMarkets 2012). The disposal of PE mulch raises many concerns. Degradation of PE mulch in landfills is negligible (complete decomposition will take more than 300 years in soil) and potentially forms environmentally harmful chemical byproducts, such as aldehydes and ketones (Hakkarainen and Albertsson 2004; Ohtake et al. 1998). PE mulch disposal (not including labor) can cost up to $236 per acre (Galinato et al. 2012; Galinato and Walters 2012). In addition, 5–10% of PE mulch can remain in the field when the mulch is removed from beds (Lluís Martín-Closas, unpublished data). On-farm burning of PE mulch can release the airborne pollutant 1,4-dioxane, among other undesirable environmental impacts (Levitan 2005).

In some areas (e.g., China and southern Spain), farmers have been incorporating PE mulch into soil annually, and PE mulch accumulation in field soil is so significant that soil water retention and crop yield are reduced (Liu et al. 2014; Steinmetz et al. 2016). PE mulch fragments from such fields are dispersed into the environment by wind and water erosion, thereby causing further pollution.

Figure 1. Typical post-season PE mulch waste ready for transport to the landfill. (Photo by C. Miles)

Plastic BDMs offer a potential solution to disposal and environmental issues associated with PE mulch use. To be a viable alternative, plastic BDMs must perform comparably to PE mulch for crop production, especially in terms of durability and weed control (Figure 2). Several studies have shown that plastic BDMs can perform comparably to PE mulch in annual vegetable cropping systems (Cowan et al. 2014; Ghimire et al. 2018; Li et al. 2014a; Miles et al. 2012; Wortman et al. 2016). Further, after plastic BDM is incorporated into the soil at the end of the cropping season, it should rapidly degrade without negatively affecting soil health. Investigations to date have revealed that degradation is a function of environment, and short-term effects on soil quality indices may be minor (Brodhagen et al. 2015; Li et al. 2014a; Li et al. 2014b). However, protracted use of plastic BDMs on soil health is not fully understood or comprehensive; long term investigations are needed (Brodhagen et al. 2017).

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