Throughout the summer, we conducted many interviews with professionals and experts in agriculture to get a better understanding as to what we want to create for growers. These conversations helped us produce a design for a cellulose-based plastic mulch that growers could use without fears of microplastic contamination in the soil after degradation. Experts in this field of research gave us many tips on how to implement this product in the field by providing us with background information on the testing and assaying to pass regulations.
Step 1: Learning What Bed Mulches Offer
Before implementing our product, it is important to understand the qualities of current products on the market. Bed mulches provide many important qualities to agriculture, such as retaining moisture in soil, suppressing weeds, and protecting against pesticides and UV light, just to name a few [1].
Eighty percent of the strawberries sold in America come from California, making plastic mulch waste a huge issue in California [2]. Bed mulches are extremely important for many types of crops, but specifically for strawberry production. This is because strawberries are very susceptible to weed competition, especially at the initial stage of planting [3]. This means fumigation is very important to strawberry growth, so bed mulches are necessary for the crop’s success and for protecting farmers.
Step 2: Addressing Safety Concerns
The Base for Our Plastic
The organism that is producing our cellulose is Komagataeibacter rhaeticus PG2, a strain that was isolated from rotten pomegranates that is not harmful to humans or crops [4]. Other K. rhaeticus strains are found in Kombucha tea or rotten fruits or vegetables [5]. This strain is not harmful and is BSL1, so it is not dangerous to work with either. Our curing process for the bacterial cellulose plastic we are creating also involves dehydration of the samples and conditions that should not allow the bacteria to survive. Therefore, our strain is not threatening upon implementation of our product.
Safety for the Common Grower
When considering the safety of putting our product on the market, we must account for the current safety features offered by bed mulches. Current bed mulches are fumigant resistant in order to protect field workers from pesticide fumigation. Fumigation is a method used for pest control that releases pesticide gas or vapor into the air or injected into the soil to eliminate pests [6]. In the interest of growers, our plastic must limit fumigation emissions and pass current fumigation standards in order to be implemented in the field. Dr. Husein Ajwa showed us around his fumigation lab, explaining the types of machinery used for testing fumigation resistance. Once we develop a viable film, we will be able to utilize these resources to test and ensure the safety of our product before releasing it on the market.
Another concern we must address is the marketability of our product. In speaking with experts and growers, we have learned that cost efficiency is a top priority. While some farms may desire a biodegradable mulch out of care for the environment, most will place more value on a cost-efficient change. We took this into account and found that a biodegradable mulch that can be tilled into the ground at the end of the growing season would save growers from paying labor costs to remove and dispose of the mulch, effectively lessening their expenses.
Step 3: Understanding the Regulations
Our team’s plan for implementation is to extensively test our plastic product using the information experts and professionals have given us. Our team has discussed the implications of creating a bed mulch replacement with Dr. Husein Ajwa. As previously mentioned, all plastics on the market need to be impermeable at the time of fumigant administration. Dr. Ajwa provided us with samples of current, industry-standard bed mulches on the market as well as prototypes of current biodegradable bed mulches. This allowed us to learn the shortcomings of current biodegradable mulches, guiding the characteristics we should strive for our plasticizer selection. Dr. Ajwa has offered to help our team test any products we produce and to give us feedback and guidance when approaching roadblocks in our design. Passing fumigation protocols will be our first step upon achieving a viable plastic product.
Step 4: Learning a Farmer’s Point of View
Furthermore, we spoke with Dave Peck, a strawberry farmer for Manzanita Berry Farms. When we presented our idea to him, he emphasized the importance of creating a film that could be tilled into the soil at the end of the growing season. Our plastic must confine fumigation chemicals and also break down into nutrients that do not harm soil. This is crucial to making our plastic marketable, since this would save farmers a lot of money by cutting out labor costs for mulch removal. For the safety of the soil, we also must be very certain of the degradation process of our mulch. In order to do this, we will study the degradation of our film prior to putting our film on the market.
Step 5: Getting Support for Our Product
Another person we reached out to is Mark Bolda, who is part of a multi-state sustainability initiative introducing growers to biodegradable mulches. Bolda travels around to growers and educates them on the benefits of biodegradable plastics over current plastics in order to push them away from using conventional PE plastics in their fields. His goal is to widely implement biodegradable bed mulches by 2030, and so he is very much in support of our endeavour. Our team has also been in contact with Mark Bolda, who guided us to study what our bed mulches will break down into after the harvest season. A lot of current degradable plastics leave behind microplastics, contaminating the soil. Understanding the breakdown of our plastic ensures we can prevent microplastic contamination, making our biodegradable plastic mulch more desirable.
Mr. Bolda also expressed interest in helping us implement our mulch once we have something to test. He expressed how important the work we are doing is and is willing to get us in contact with growers when we have a product in the testing process.
Step 6: Understanding the Breakdown of Materials
As mentioned, many growers are unhappy with current biodegradable bed mulches on the market because of microplastic contamination after degradation. These responses motivated our team to ensure no microplastics or harmful degradation products will be left by our mulch. To combat this, we made sure all proteins and compounds added into our cellulose are going to be natural and easily broken down. From literature, we know cellulose breaks down into glucose monomers that bacteria in soil can use as nutrients to encourage microbial growth, which is beneficial for soil health [7]. On top of the cellulose degradation, understanding plasticizer and CBM breakdown is important. In speaking with Dr. Lisa DeVetter, an expert at the forefront of development of biodegradable agricultural films, we learned about various assays to test that the degradation processes of our films are compliant with USDA, NOSB, and ASTM standards. These include compostability assays and a mesh bag study. This will allow us to test the degree of degradation, time length of degradation, and degradation products.
We wanted to make sure the plasticizer we used was natural and fully biodegradable. In compliance, our plasticizer testing focused only on those that are bio-based, a term coined by the USDA meaning “in whole or in significant part, of biological products or renewable domestic agricultural materials (including plant, animal, and marine materials) or forestry materials OR an intermediate feedstock” [8]. Our current material composition involves the use of glycerol as a chemical plasticizer and citric acid as a cross-linking agent, both of which are non-toxic metabolic products present in the human body. Additionally, citric acid and its breakdown components are already approved by the FDA for use with humans. This combination has been tested with cellulose to yield increased flexibility and tensile strength, both of which are high priorities for growers [9].
We interviewed CBM and polymer film expert Oded Shoseyov, who confirmed that since CBMs are protein subunits, the simple breakdown products of CBMs will be amino acids. Upon inquiry about the effects of an influx of amino acids on the soil, we learned that the effects would be negligible. Our product design is in accordance with current USDA standards pertaining to biodegradable films in that it is entirely made of biobased components. This moves us one step closer to the creation of a market-ready biodegradable film.
