By Laura Sorkin

As a farmer and consumer, I’ve accepted plastic as being necessary in my life but cringe at the amount of waste it causes. I use plastic containers in my greenhouse but encourage my clients to return them to me at the end of the season where I wash them and reuse them. I reluctantly request plastic bags at the grocer but save them and bring them to farmers’ market where customers gladly accept them for their produce. One aspect of using plastic in my business that grates on me that I cannot remediate is the use of black plastic mulch for long-term crops. There is no doubt about the benefits of plastic mulch: it warms the soil, retains nutrients and moisture and, most importantly to the small organic farmer, suppresses weeds. I have tried to grow long-term crops such as winter squash without laying down plastic and it has ended in frustration and low yields. Furthermore, the warming qualities of the black plastic makes growing heat-lovers like melons and eggplant more reliable crops here in northern Vermont.
Though I have come to rely on these benefits, I realize that our farm produces yards of plastic waste each year that cannot be recycled or reused. In addition, the task of removing the plastic from under a mat of vines is one of the least favorite on the farm. Each year during foliage season, rather than winding down into a zen-like state knowing the bulk of the year’s work is over, I find myself struggling with a mile-long length of plastic that is weighted by mud and a season’s worth of prickly squash stems.
The solution would be to find a biodegradable mulch that had all of the qualities of plastic but broke down into the soil by the end of the season. Furthermore, it could not be significantly more expensive given the small margin of profit produced by most crops. My search revealed that there is not a lot out there that has been trialed extensively or successfully by small farmers. In the end, I found two possibilities: a cellulose-based material called BioBag Agrofilm, from Italy, and Kraft paper, also known as Planter’s Paper. Both were more expensive than the plastic per foot but there would be no disposal fee nor any need to expend labor to remove them from the field at the end of the season. Curious to see which material ended up costing the least when all of the variables were accounted for and whether yields would be comparable, I applied for a SARE Farmer/Grower grant and was approved to conduct an experiment in the summer of 2005 (FNE05-562).

Trial details
The experiment was conducted in three different plots randomly selected throughout our 6-acre field. One plot was planted with ‘Expert’ pumpkins; one with winter squash Delicata and Butternut; and one plot with ‘Festival’ watermelon. Each plot had one row of plastic adjacent to one row of Agrofilm adjacent to one row of Kraft paper. All of the following data were recorded for our analysis: hours required to lay each material plus extra hours needed to maintain any of the rows; yields from each crop from each material; time necessary to remove the plastic at the end of the season; costs per foot for each material as well as disposal fees for the plastic.
The following figures are based on labor costs (which include hourly wage, taxes, and workers’ compensation) at $20 per hour Disposal of the plastic was $15 per yard The plastic cost $73 for a 4’ x 2,000’ roll. The BioBag Agrofilm cost $335 for a 4’ x 4,000’ roll. The paper cost $200 for a 4’ x 1,500’ roll. All of the above costs include shipping.

Cost per foot = Cost of materials + time in labor for laying, maintaining, and removing and disposing (where applicable)

Pumpkins: Plastic $0.21/foot
Agrofilm $0.19/foot
Paper $0.35/foot

Winter squash: Plastic $0.20/foot
Agrofilm $0.19/foot
Paper $0.34/foot

Watermelon: Plastic $0.21/foot
Agrofilm $0.20/foot
Paper $0.35/foot

Yield per dollar spent

Pumpkins: Plastic 2.71 lbs./$
Agrofilm 3.19 lbs./$
Paper 0

Winter squash Plastic 2.98 lbs./$
Agrofilm 1.78 lbs./$
Paper 0

Watermelon Plastic 11.16 lbs./$
Agrofilm 6.2 lbs./$
Paper .78 lbs./$

Allow me to immediately eliminate the paper as a possibility for commercial growers. I had heard that the paper was difficult to work with but there were not many options to choose from and I was curious to see for myself. The per-foot costs associated with the paper turned out to be significantly higher than the other materials for several reasons. First, the cost of the material itself was comparatively expensive; one and a half times higher than Agrofilm and more than three and a half times higher than plastic. Second, the paper took a great deal more time to lay than the other two materials due to the fact it tore easily using our mulch layer as intended. In fact, after much frustration and torn paper, we had to remove the rear discs that are designed to throw dirt over the edges and instead hoe dirt by hand to tuck it in. After this effort, the paper tore down the middle like a zipper being undone on plot one and two within two days after a mild breeze caused it to flap. The paper in plot three tore halfway down the row. No effort was made to weed in these rows and consequently there were zero yields in the paper rows of plot one and two and only a small yield in the paper row of plot three. I would not recommend the paper mulch for any field application.
The results were more promising when looking at the data for the Agrofilm. Our results showed the yield per dollar spent was better in the plastic mulch for winter squash but higher for the Agrofilm in the pumpkin patch. I cannot explain these differences but can conclude that the Agrofilm is a viable contender to compete with plastic under squash crops. In the watermelon plot, however, the plastic was clearly the winner, yielding twice as much as the Agrofilm. A possible explanation may be that warm soil is more important for melons and the plastic retained more heat which resulted in larger fruit in the plastic-watermelon row. There have been other experiments, however, that showed no difference in melon yields between the AgroFilm and plastic. I found a study done by Rangarajan, Ingall and Davis, (Alternative Mulch Products 2003, Cornell Univ, Ithaca, NY) that compared the two products which showed melon yields comparable to black plastic on one farm and nearly as high on another farm growing melons. Where heat is not as much of a factor in the pumpkins and winter squash, the variances may be attributed to local fertility or weed pressure despite our efforts to ensure the same conditions for all of the crops.
The Agrofilm looks and feels very similar to black plastic, though it is not as thick. According to the web site, it is made with all natural ingredients, including non-genetically modified cornstarch. I had used it under other crops that were not part of the experiment such as eggplant and we produced nice fruit all summer long. The material began to erode by late summer and by the fall had almost disappeared. The ground underneath remained bare, I presume because the material smothered or baked the weeds that popped up underneath. Best of all, there was no grimy mulch to pull up; we simply tilled the crop under and used the time for other fall chores. One consideration for organic farmers is that the product does not yet have OMRI approval for use in organic farms. NOFA-VT has approved its use so if you decide to try it, you may wish to check with your local organic certifier first.

Other options
A similar mulch that was not in the experiment is called Biotelo; it is also an Italian product made with the same cellulose material called Mater-bi. According to NOFA-VT, several Vermont farmers are going to be using it in their fields this season so perhaps more information soon will be available as to its efficacy.
I would encourage agricultural firms to continue research into other affordable forms of biodegradable mulch film for commercial farmers. Just from speaking to other farmers who also have concerns about plastic waste, I believe there is a considerable market for it. It would be especially beneficial if the materials used for manufacture were natural byproducts of other industries such as spent grains from breweries or low-grade wool that otherwise have little commercial value and likely end up wasted. This year I plan on reducing my use of plastic to the melons only and will plant all of my other long-term crops into the biodegradable mulch. I will still be tossing a little plastic in the fall but considerably less than years past. Hopefully that is a trend we can continue on the farm and in our lives.

For more information about Agrofilm log on to www.biobagusa.com or phone 727-789-1646. For more about Biotelo log on to www.DuboisAg.com or phone 800-667-6279.

Laura Sorkin of Cave Moose Farm can be reached at lauraglenn@hotmail.com.