Frequently asked questions about biodegradable mulching

Currently, there’s a wide variety of mulch used in agriculture to improve the quality of the land and crops. Among them are biodegradable mulch, which is becoming increasingly popular thanks to their characteristics that make them more economically efficient and environmentally friendly. In this article, we’ll talk about their advantages and disadvantages, and the details that make them special when compared to other types of plastics.

What is biodegradable mulch?

These are plastic films that can biodegrade as a result of the action of microorganisms such as bacteria, fungi or algae. The biodegradation process produces carbon dioxide, water, inorganic compounds and biomass, which are not only harmless to the soil and crops, but also an additional source of fertilization, although limited, of course.

It’s important to make a distinction with oxo-degradable plastics, which are manufactured from conventional polyethene with oxo-fragmentable additives that break down the polyethene into small pieces, thus favouring the contamination of agricultural soils with microplastics.

Why use biodegradable mulching?

For some years now, there has been an increase in campaigns focused on raising awareness among the population regarding the importance of reducing the use of plastics and products that contain them. As a result of that, more companies and agricultural producers are looking for alternatives that allow them to use mulching that, aside from being more environmentally friendly, allows them to maintain the quality of the products they grow.

One of the best alternatives is biodegradable mulch, since, although many of these plastics are made from polymers, they can biodegrade and serve as a compostable material to reduce environmental impact as they end up being incorporated into the soil.

In addition to the action exerted by microorganisms such as bacteria, fungi or algae, the degradation of biodegradable mulch is caused by the intervention of diverse factors such as climate (relative humidity, rain, temperature…), solar radiation received and the growing season among others, so farmers are attentive to establish the most appropriate time for ploughing, which will end the degradation process.
Now, before using biodegradable mulching, an exhaustive analysis or specific tests must be made to determine whether the intended use of the plastic is appropriate, thus guaranteeing the expected useful life of the film.

Advantages of biodegradable mulching:

• Prevent the proliferation of weeds
• Retain soil moisture better
• Improve and protect the structure of the soil bed
• Allow saving more water
• Allow saving on fertilizers
• Allow better temperature control (heating or cooling)
• Control pests (reflective mulch)
• Higher crop yields are achieved
• No plastic waste to collect after harvest
• Prevent soil contamination by not producing toxic waste after use
• Help preserve soil nutrients and improve fruit and vegetable growth
• Don’t contain heavy metals
• Their installation is a standard procedure that doesn’t require special machinery

Disadvantages of biodegradable mulching

Like all products that have positive qualities and bring benefits to farmland, there are certain disadvantages to consider when choosing biodegradable mulches.

• They have a higher cost, compared to other conventional polyethene plastics (in some countries this factor is mitigated by subsidies that promote their use and, on the other hand, there is also the savings implied by not having to collect plastic waste after harvest).
• Some of these plastics may be more sensitive to the action of temperature, the pH of the growing soil and the humidity of the area where they are used (the more humidity there is, the more likely the degradation process will be accelerated).
• The biodegradation process starts in the buried part, as opposed to the exposed part of the film whose biodegradation process will be slower.
• Depending on the thickness of the biodegradable mulching, its degradation may begin earlier than expected (between 2 and 3 months).

Although the disadvantages of these mulches are directly related to the degradation process, these are outweighed by the benefits they offer to crops. Today, there is a great diversity of fruits and vegetables that are cultivated with biodegradable mulch, for example, bell peppers, tomatoes, eggplants, zucchini, watermelons, melons or cantaloupe and lettuce.
Among the market’s innovations are black micro-perforated mulches for the specific cultivation of asparagus, black/white natural mulch for melon or cantaloupe cultivation and clear mulch for corn. For further information, we recommend reading our article on biodegradable films in agriculture: advantages, disadvantages and their different applications.

Things to consider

When choosing which type of mulch to use, it’s necessary to analyse certain aspects. One of them is the cost, however, it is not all about the price of the plastic, it is also important to consider its characteristics and the benefits it brings to the soil.
According to Javier Pery, Product Manager, and Sara Erlbacher, Export Sales, members of the Armando Alvarez Group, several factors make up the final and total cost of biodegradable or polyethene mulch such as:

• Purchase price of mulching (PE vs. BIO)
• Thickness chosen (the thicker the plastic, the higher the cost per acre)
• The cost of removing mulch from the soil after use varies according to:
  • Manual or mechanized recovery
  • If it is performed briefly or in-depth
  • Mulching thickness
• Cost of transportation to the recycling site and possible recycling charges
• Environmental subsidies

For more information, we recommend watching our Webinar on biodegradable mulching: benefits and profitability.

How to select the type of plastic mulch?

Once the grower has decided to use biodegradable plastic mulchbiodegradable plastic mulch on his crops, one of the first aspects to know is what type of mulch to use.

Biodegradable plastic mulch must comply with the standard EN 17033:2018 or be certified as OK Biodegradable Soil. This is one way to ensure its proper performance in the cultivation soil.

The selection of plastic mulch will depend on the type of soil, the type of crop in which it will be used, and the climatic conditions of each region.

It is always advisable to carry out prior studies of the aspects mentioned above, as well as to consult your distributor to find out the best solution in each case before acquiring a particular type of mulch.

How should the soil be prepared to place the biodegradable mulch?

This is certainly one of the aspects that should not be neglected because biodegradable mulches will have a better performance depending on the condition of the soil and the conducive conditions that are created.

The soil should be prepared in advance to prevent leaving behind stones or other sharp and protruding objects that could stick out of the ground and damage the plastic.

Growers must be very careful to avoid installing plastic mulch on soils with high moisture levels or, on the contrary, when organic fertilizer has been incorporated into them to avoid the premature degradation of the mulch.

It’s important to be very careful to avoid placing the plastic immediately after the application of organic fertilizers. The ideal scenario is to wait at least four weeks to ensure that no residues remain, otherwise they may accelerate the biodegradation of the biodegradable mulch as a result of microbial activity associated with the fertilizer.

Placing biodegradable mulching

The installation of biodegradable mulch is a standard procedure that doesn’t require special machinery, so the same equipment can be used when laying conventional polyethene mulch.

However, it’s important to reduce the film tension and machine speed when placing the biodegradable mulch to avoid tearing or deterioration due to excessive stretching.

It is recommended that growers preparing the land for the placement of the mulch dig a small trench or furrow where they can place the irrigation tape so that it doesn’t come into direct contact with the plastic film, avoiding possible burning of the drip lines.

It’s also necessary to work on non-compacted soil to avoid the risk of breakage of the plastic with the sharp clods or stones that may be present in the soil. For more information on this subject, we recommend you read the following article.

How do I begin planting?

The long-awaited moment has arrived: planting, and to do so it is best to proceed immediately after having placed the biodegradable mulch, so you can take full advantage of all its benefits.

Keep in mind that planting should never exceed 4 days after the installation of the plastic since premature degradation by solar radiation may occur and the properties of the film would no longer be the same.

It should be remembered that the use of biodegradable plastic mulch doesn’t imply variations in water consumption, irrigation flow, or changes regarding a conventional plastic material.

Storage of biodegradable mulching

Due to the special characteristics of this type of film, it is recommended to store biodegradable mulch in a warehouse that’s properly conditioned to protect it from humidity, sunlight and other heat sources that may compromise its integrity and quality, as well as to try to keep it in its original packaging.

One of the recommendations always made to growers is to use the mulch in the same crop season, once purchased, even though plastic mulch rolls can be stored and kept for a reasonable period of time.

However, it all depends on whether the plastics are properly stored and protected according to the manufacturer’s instructions. Improper handling during storage can cause damage to the core or to the plastic sheet, compromising its integrity and affecting the unwinding process.

How should mulch be handled after cultivation?

As we have mentioned, the degradation of a plastic mulch with biodegradable qualities will depend on factors such as climate, temperature, microbiological agents in the soil, humidity, and handling. However, once cultivation is finished the plastic can be left in the soil to finish degrading completely.

“Its final biodegradation will be favored if it is broken into small pieces, using a disk harrow or similar, and if the remains are buried, using a milling machine pass or chute. Also, favoring the activity of microorganisms through the contribution of organic matter and moisture will facilitate the biodegradation process, for example, with subsequent cultivation of green or horticultural manure,” according to the information reflected in the Plasticulture Workshop conducted between Earth University and Armando Alvarez Group.

Some comparisons between plastics

Although more growers and companies are leaning towards the use of biodegradable mulch, there are still some who have doubts about it. The following is a brief comparison of biodegradable films and conventional polyethene films.

Polyethene films:

• They are most frequently used in traditional agriculture.
• The correct disposal process is to collect the used plastics from the field, once the harvest is finished, and deliver them to an authorized manager of used agricultural plastics who in turn transports them to a recycler who will recover them.

Biodegradable mulching:

• They have the same benefits as polyethene mulch.
• Their biodegradable quality has an important advantage since these plastics don’t have to be removed at the end of the harvest.
• It’s more environmentally friendly.
• It can be tilled directly into the soil at the end of the season.

Cost of polyethene mulch vs. BIO:

When deciding which mulch to use, we should not only consider the purchase price of the plastic because several factors make up the total cost as we mentioned before.

Case study with the cultivation of Melon/Cantaloupe in Murcia, Spain

After comparing both plastics, it is evident that, although more expensive, the biodegradable mulch saves much more money in terms of labour costs in the long term, especially at the time of removing the conventional plastics and disposing of them at the end of the harvest.

Installing the biodegradable mulch can be done with the same equipment as traditional plastic mulches, while the plastic waste that is collected and disposed of at the end of the crop cycle is reduced to zero, as it simply remains to be ploughed along with the rest of the soil and vegetation.

Plastic biodegradation doesn’t cause soil contamination and reduces global greenhouse gas emissions significantly.

Additional data

There may be differences in quality between biodegradable mulching from different manufacturers, as each company involved in their production will have different technologies, knowledge and raw materials that will result in better performing end products.

The degradation time may vary according to the factors influencing biodegradable mulches. For example:

• Film thickness
• Type of crop
• Geographic location
• Irrigation
• Raw materials
• Colour of the mulching

Hence the importance of knowing how to choose the mulching that suits your needs.

The competitiveness of using mulching, biodegradable or not, will depend on factors such as production costs, purchase prices of necessary inputs or logistics. Usually, the more larger the production area, the better the economic payback conditions.

As these are biodegradable mulching, made from biopolymers, it’s important to know that their mechanical properties are a little lower, so applying the mulching with excessive tension may cause breakage. Therefore, it is recommended to reduce the tension during the installation of this type of mulching.

Once the crop is harvested, you can cultivate immediately in the same area, unless something unexpected that requires additional attention happens with the soil. The pigments used in the production of biodegradable films are also biodegradable and completely harmless.

Biodegradable mulching recommendations:

We’re having a very busy time in the garden. Because of late cold weather followed by too much rain at once, all our transplanting has been delayed. We’re up-to-date in the permanent raised beds – we’ve planted out lots of lettuce, senposai, early cabbage, scallions, our first cucumbers and summer squash, and chard, tomatoes, eggplant, celery and okra. We’re also up-to-date on raised bed sowings of carrots, turnips, beets, snap peas, snow peas, bush beans, edamame and asparagus beans. But in the row-crop areas, it’s a different story. We have planted out our main-crop cabbage and broccoli, our “spring” potatoes and sown our first corn. We’re about a week behind on our big transplantings of Roma paste tomatoes, peppers, melons, sweet potatoes, and therefore watermelons. It’s also time to sow more beans, cucumbers and squash. But we’re getting to it as fast as we can!

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  made in 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  and is accepted for organic farming in Canada. 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 explain how we lay these biodegradable mulches without benefit of a machine. Sorry for the delay in posting. I’m making some improvements to my website, honest!