2014 24.1 Biodegradable Mulch Films in Organic Production: National Organic Program Considers Rule Change

The U.S. Department of Agriculture (USDA) National Organic Program (NOP) is considering whether to authorize the use of biodegradable plastic mulch films for certified organic production. In January 2012, the Biodegradable Products Institute (BPI) petitioned the NOP to allow the use of biodegradable plastic mulch made from bioplastics for certified organic production. In October 2012, the National Organic Standards Board (NOSB) voted 12-3 to formally recommend approval and in August 2013, the NOP issued a solicitation for public comment through October 2013. As of this publication, the recommendation has not been formally accepted by the NOP. So while these materials may be allowable in the near future, current use of biodegradable plastic mulch in U.S. certified organic production remains prohibited.

Proposal to add biodegradable biobased mulch film to the list of approved materials
The NOSB recommended that biodegradable biobased mulch film be added to the national list of approved materials for use in organic crop production. They saw the use of this material as an opportunity to reduce landfilling of traditional, petroleum-based plastic mulches, without sacrificing organic farming principles. While non-degradable plastic mulches are currently allowed in certified organic production, they must be removed at the end of each growing season.

The NOP has therefore proposed an amendment to allow biodegradable biobased mulches for certified organic production. The proposal would allow producers to leave biodegradable biobased plastic films in the field provided they meet certain criteria. That is, the mulch must meet certain compostability standards: it must biodegrade 90% in less than two years, and must be biobased. It would then be the growers’ responsibility to manage their fields such that these mulches do not accumulate in the soil.

Biodegradable and biobased

Many agricultural plastics are advertised as “biodegradable”; however, claims of biodegradability must be evaluated carefully since the protocol suggested in the NOP proposal involves composting, not soil degradation. The proposed amendment states that “Biodegradable mulch… is left in the field to biodegrade,” and proposes to use ASTM International standards D6400 and D6868, to measure the potential biodegradability of mulch.
ASTM International (www.astm.org) has prepared a series of standards for “compostable plastics” to measure biodegradability under municipal or industrial composting conditions (ASTM D6400). To meet ASTM D6400, 90% of carbon (C) atoms in the mulch must be converted to carbon dioxide (CO2), by microorganisms within 180 days. Therefore, many mulches claiming to be “biodegradable” are actually “compostable”, that is, they fulfill the requirements of ASTM D6400, or related standards.

Biobased is defined as commercial or industrial products (other than food or feed) that are composed in whole, or in significant part, of biological or renewable domestic agricultural materials (including plant, animal, and marine materials) or forestry materialsi. In the NOPs proposed rule, biodegradable mulch must be biobased with its content determined using ASTM D6866.

Reasons in favor of the rule

Most of the comments received by the NOP supported the use of biodegradable biobased mulch films in certified organic agricultureii. Supporters cite the potential reduction of landfilled plastics as the primary benefit of the proposal.

Additionally, many commenters supported language specifying that the use of proscribed materials or methods be specifically addressed in the rule, citing that genetically-modified organisms should not be allowed in materials used in certified organic production. A position that the NOP acknowledged is covered by existing regulations.

Recent research on biodegradability in soils raises concerns

One comment in opposition to the proposed amendment was based, in part, on a three-year USDA, National Institute of Food and Agriculture (NIFA) Specialty Crop Research Initiative (SCRI) Standard Research and Extension Project (SREP) entitled Biodegradable Mulches for Specialty Crops Produced Under Protective Covers (NIFA Award No. 2009-02484)iii. This project, which concluded in 2013, was carried out by investigators from Washington State University, Texas Tech University, and the University of Tennessee at Knoxville, among others.

In one study, this group assessed the impact of soil incorporation on mulch biodegradation and soil quality. During that study, mulch samples were recovered from the soil every six months for 24 months after burial, the mulch was then evaluated for percent surface area degradation and the soil was assessed for potential changes in quality.

According to their comment, signed by five of the project investigators, they agreed that “truly biodegradable” mulches could provide the “highly desirable goal” of reducing petroleum-based plastic waste. However, the group suggested further revision of the proposed rule was necessary to “retain organic farming principles”. Therefore, the group could not support the proposed amendment as written, citing the following reasons:

  1. Composting standards are not an appropriate way for evaluating mulch biodegradation in the soil; methods specifically targeting soil environments need to be used instead.
  2. The ‘Biobased’ definition provides inadequate information regarding what type of products will be allowed and what will be prohibited.
  3. Inadequate data are available regarding potential long-term accumulation of mulch-associated recalcitrant (not biodegraded) or environmentally deleterious materials, such as microscopic plastic polymers that are visually undetectable but are not fully degraded, and/or additives such as dyes and fillers that will remain in the soil and whose effect on soil ecology is unknown.
  4. It is not clear if the proposed amendment’s biodegradability specifications refer to mulches as received from the vendor, mulches exposed to weathering, or both.

The field is not a compost pile

The proposed rule uses ASTM D6400 and D6868 as the standards for compostability. These standards are limited to composting and do not address biodegradation in the soil (field) environment. The group distinguished the soil environment from the composting environment, and stated that “currently there is no evidence to show that a product that biodegrades while composting will also sufficiently (≥90%) biodegrade in the soil.”

A more appropriate standard for measuring the biodegradability of plastics in soil is currently being developed by ASTM International (Work Item 29802) entitled Aerobically Biodegradable Plastics in the Soil Environment. In this new standard, biodegradable mulches must break down into CO2, water, and environmentally benign substances within one or two years, leaving no harmful residues. However, because their research demonstrated evidence of incomplete biodegradation of biodegradable plastic mulches after 24 months of burial in soili, the SCRI research group believes that further studies should be conducted with potentially biodegradable plastic mulches to verify whether they biodegrade in the soil within a reasonable time frame (18-24 months), leaving no residues, fragments, or by-products in the soil which could negatively impact soil and/or plant health.

“Biobased“ may not be enough

According to the proposed rule, manufacturers of biobased mulch film must certify their product under the USDA BioPreferred program. However, product formulations change frequently, as feedstock prices fluctuate and new technologies arise. Therefore, the group questioned what would trigger product review after initial approval and commented that both approval and enforcement might be a challenge.

The research group sees these issues as problematic, and believes it “…would be useful to both the agricultural and plastics industries to provide names of specific polymers that can be synthesized from renewable sources and are proven to be biodegradable in soil.” Adding such direct and unambiguous feedstock specifications would help alleviate questions and challenges from both manufacturers and regulatory agencies.

Accumulation of plastics in the soil

Agricultural mulches are typically applied every year, and biodegradable plastic mulches would be no exception. In a system where the mulch would be incorporated into the soil instead of being removed, the potential for accumulation is high. Under the proposed rule, approved mulch must deteriorate 90% within two years. Assuming  a mulch was able to meet the standard by degrading 45% each year in the soil, there could be as much as 165% of the bed area in mulch fragments (100% from the current year, 55% from the previous year, and 10% from two years prior). In the WSU study, the SCRI research group tested three mulch products in a 24-month burial test and found that none of the mulches tested would have met the proposed standardi (Figure 1).

Additionally, the NOSB recommendation proposed that organic growers take appropriate actions to ensure complete degradationiv of biodegradable plastic mulch products on their farms, underlining the importance of evaluating on-site degradation. Another study carried out by the SCRI research group tracked deterioration of biodegradable plastic mulch in a production environment using photographic image analysisv. This method could be employed by growers to track degradation of mulch in their fields, but no research studies have been found that identify steps growers can take to improve or speed up degradation once mulch is soil-incorporated. And once mulch has been tilled into the soil, it would be impractical, if not impossible, to remove it from the field if it fails to degrade.

An ambiguous rule

While the SCRI research group argues the incompatibility of the composting standard with materials to be used in the soil environment, they express further concern with the lack of specificity in regards to the state of mulch as it is tested. That is, to be approved under the rule, would new mulches be evaluated for biodegradability, or would manufacturers be able to use weathered mulches?

The group found that weathered mulches biodegraded significantly faster than new mulches. But, what level of exposure, and in what conditions, could mulches be used for testing? These questions led the SCRI research group to recommend against adopting the proposed amendment.

In conclusion

Biobased, biodegradable plastic mulch presents a great opportunity to cut down on the expanding waste stream due to non-degradable plastic mulch use in agriculture. However, the use of biodegradable plastics in certified organic production may not be ready for prime time. According to one group of university researchers, more needs to be known about the source and ultimate fate of biodegradable plastic films in the soil environment before they should be permitted in certified organic production. Additionally, the researchers encourage the NOP to update the language to ensure consistent interpretation and application of the new rules regarding biodegradable plastic mulch. Regardless, the overwhelming support for the approval of biodegradable plastic mulch for certified organic production, among those who participated in public comment, indicates a growing demand for more sustainable technologies in agriculture.

What’s next?

The NOP has already begun publishing new rules that were proposed at the same time as the biodegradable mulch proposal. If the NOP decides to permit biodegradable, biobased mulches in certified organic production, the new rule could be established at any time—although Reginfo.gov estimates that final action on the proposal will not happen until June 2014.

Regardless, if biodegradable mulches are accepted, be sure to contact your organic certifying agency before you incorporate them into your field production plan.

iCorbin, A., Cowan, J., Miles, C.A., Hayes, D., Dorgan, J., Inglis, D.A., 2013. Using Biodegradable Plastics as Agricultural Mulches. Washington State University Extension Publication FS103E. 6 p. http://cru.cahe.wsu.edu/CEPublications/FS103E/FS103E.pdf.
ivCorbin, A.T., Miles, C., Cowan, J., Hayes, D., Moore-Kucera, J., and Inglis, D. 2013. Current and future prospects for biodegradable plastic mulch in certified organic production systems. http://www.extension.org/pages/67951.
vCowan, J.S., D.A. Ingles, and C.A. Miles, 2013. Deterioration of three potentially biodegradable plastic mulches before and after soil incorporation in a broccoli field production system in northwestern Washington. HortTechnology 23(6):pg849-858.

Tags: Biodegradable Biobased Mulch, Biodegradable Plastic Mulch, Biodegradable Plastic Mulch Films, BioPreferred, Mulch