Qualified praise for biodegradable plastic mulch

We’ve added in late afternoon transplanting shifts, and some random evening weeding (which has helped us get the first round of carrot and beet thinning done). Yesterday I measured and flagged the areas for Roma tomatoes, peppers, melons, beans, edamame, watermelon, and sweet potatoes. I set out the mainline tubing for the drip irrigation and dropped the shuttles of drip-tape at the ends of the patch. I wrote about our drip tape shuttles a while back. They are part of our commitment to minimize our agricultural plastic usage by making our plastic stuff last. The shuttles let us fairly easily reuse the drip tape.

After running out the drip tape, flushing the lines, capping them off and testing (and fixing!) any leaks, next we’ll roll out biodegradable plastic mulch. This wonderful product has changed our lives! And yet we are not all firmly convinced it is an ecological choice. The language in the accessible information can be confusing.

We like using biodegradable plastic because it warms the soil, leading to much earlier crops, it keeps the weeds down for a few months, and then it falls apart, so we don’t have to remove it and add to the heaps of agricultural plastic trash. It’s especially good for vining crops like watermelons and sweet potatoes, because by the time the mulch disintegrates, the vines cover the ground and weeds have little chance. Why we qualify our praise is because it has been hard to find out what it’s made of, and what it disintegrates into. And for some, there’s that knee-jerk reaction to anything plastic!

Biodegradable is not the same as bioplastic, nor as bio-based. Bioplastics are a type of plastic made from biological substances rather than from petroleum products alone. Some are biodegradable, some are not. Wikipedia distinguishes two types of bioplastics: 1. Oxo-biodegradable plastics (made partly from natural sources, with non-biological additives) – they break down into biodegradable materials; and 2. Plastics made wholly or in part from vegetable material. The second type are often made of cornstarch or sugarcane, but could be made from other agricultural crops. Some biodegrade, others don’t (eg. those made from sugarcane ethanol). I found the Wikipedia explanations confusing and some read as if they were funded by petrodollars: “It is difficult to see why . . . resources . . . should be used to produce them when the raw material for conventional plastics is so inexpensive and is available in unlimited quantities.” Really.

I found a European Factsheet on bioplastics which clears some of the confusion. There are conventional (petroleum-based) plastics and there are bioplastics. Bioplastics may be divided into three categories. The first is the bioplastics which are not biodegradable. The other two are biodegradable, and differ in whether or not they contain fossil-based materials or only bio-based materials. Our goal would be to get biodegradable bio-based materials.

The two most commonly available biodegradable plastic mulches in the US are Eco-One and Bio360 from Canada. Novamont, an Italian company, imports Biotelo, the original mulch film made from their product Mater-Bi.

Eco-One describes itself as Oxo-degradable. It claims “Environmentally sound degradation: Laboratory studies indicate that this degradable plastic breaks down into CO2, H2O and biomass without toxic residues. Degrades fully both above and below the soil.” It’s available clear (for encouraging early emergence of sweet corn) and black, including an extended lifespan version for those wanting a 5-6 month window before it degrades, rather than the usual 3-4 months.

Bio360 is made by Dubois. It’s entirely biodegradable, and made from Mater-Bi, a non-genetically-modified starch with vegetable oil resin. Mater-Bi® is a wide family of fully biodegradable bioplastics, sold in pellet form to the industry of bioplastic converters. Mater-Bi®’s ingredients consist of plant starches, “mainly corn starch, with fully biodegradable aliphatic-aromatic polymers from both renewable raw materials (mainly vegetable oils) and fossil raw materials. Mater-Bi breaks down into carbon dioxide and water, with no mulch residues in the soil.” (see also the Cornell University 2006, Biodegradable Mulch Product Testing). Ah! So even Mater-Bi contains some fossil raw materials. And of course, fossil fuels are used in the manufacturing process. Life is so full of trade-offs!

I found explanation of the chemistry from the Biodegradable Products Institute, as part of a 2012 petition to the USDA National Organic Standards Board to allow “Biodegradable Mulch Film Made From Bioplastics”. The bioplastics they were petitioning for are not polyethylene like regular plastic mulch, but “polyesters, polymers formed by the reaction of a hydroxyl group and a carboxyl group. The natural world is full of ester linkages. Living cells and organisms have developed enzymes to hydrolyze the ester linkage. Examples of natural esters are fats and oils, where three fatty acid molecules are esterified to glycerol/glycerin; natural waxes, where long-chain alcohols are esterified to a fatty acid; and some natural flavors, such as banana flavor, n-amyl acetate, an ester of n-amyl alcohol and acetic acid.” Biodegradable bioplastic mulch film materials can contain carbon black to make the film black to absorb heat from the sun. Or titanium dioxide to create white mulch, which can cool surface soil temperatures slightly, by reflecting most of the sun’s heat.

NatureWorks™ PLA INGEO, Ecoflex® F Blend C1200, Ecovio® F Film and Ecovio® F Blend, Mirel™, were also listed in the petition as suitable Biodegradable Mulch Films made from bioplastics. In contrast, oxo-biodegradable materials were not included in their petition, because they did not fulfill the two criteria proposed to address the concept of “fully biodegradable plastics”.

The Organic Standards are inconsistent, as §205.206(c)(1) permits “mulching with fully biodegradable materials” but §205.206(c)(6) requires that “plastic or other synthetic mulches . . . are removed from the field at the end of the growing or harvest season.”

I’ve been buying from Nolt’s Produce Supplies in Leola, PA (717) 656-9764. They sell Bio360 BTB645 4' x 5000' for $345 plus shipping, and Eco-One E1B548 4' x 8000' for $243 plus shipping. They are a company that doesn’t use email or websites, and they’re closed on major Christian holidays, so don’t call then! Johnny’s sells 32' lengths for $17.95. Robert Marvel sells whole rolls of Eco-One and Bio360 (call for prices).

The first biodegradable plastic we used was Bio-Telo, (Mater-Bi). Since then we have sometimes bought that and sometimes Eco-One. I had not appreciated the difference. Knowing what I know now, I’ll buy the Mater-Bi types in future, rather than the oxo-biodegradable ones.

Next time I’ll write about how we set out biodegradable mulches without the use of any machines. Sorry for the delay in posting. I’m working on making improvements to my website, honest!

The Case of the Unapproved Biodegradable Plastic Mulch

I wrote this article for ACORN’s summer 2015 newsletter and am now republishing it here.

At the end of March of this year (2015), we found a memo in our inbox from Ecocert (the organic certifying body that we are certified with). In this memo, we were told that we would no longer be able to use the biodegradable plastic mulch (made with non-GMO corn starch) that we had been using unless we removed it after use. We were surprised and concerned. It was definitely a little last-minute! We still had leftover rolls of it at the farm from last season and had made our order for this season back in December (when we do a lot of our inputs purchases). And the removal part….it’s pretty tough to completely remove something that biodegrades as it’s in use.

Bryan and I have been using biodegradable plastic mulch (which I will refer to from now on as biofilm to reduce typing) since the first year we started Broadfork Farm. As small farm operators, we have appreciated the reduction in our time spent weeding in particular. But there are other benefits to using plastic mulch, like warming the soil and retention of moisture in the soil. With our deep feelings of stewardship for the soil, we have also liked how we have been able to keep more of the soil covered during the season (with the biodegradable mulch in the beds, our pathways have been maintained in living mulch that we mow). Soil left bare tends to create its own “cover” of a dry, dead, erodible soil layer.

We knew that, as a manufactured product, biofilm wasn’t the perfect solution in our utopian organic vision. But it was a solution we preferred to regular plastic mulch (with the required pulling up at the end of the season and taking to the landfill) or frequent cultivation. There are of course other mulches like straw or leaf mulch but they didn’t fit in as well with our whole system (but rather have fit in with some crops in certain instances when we could access sufficient quantities without prohibited substances).

HuaWei，biodegradable plastic mulch.