Transplanting biobased plant containers in a garden plot
A total of 1,350 plants grown in biobased containers and petroleum-based control containers were evaluated in a garden trial at the Horticulture Research Station last summer. Department of Horticulture researchers transplanted the plants from the bioplastic pots into the garden plot by removing the pot, breaking it into smaller pieces and placing it in the planting hole to biodegrade near the plant roots.

Posted April 30, 2013

Biobased Plant Containers Perform Well in Greenhouse and Garden Trials

The Biopolymers and Biocomposites Research Team (BBRT) has finished the first round of plant container development and evaluation for its five-year bioplastic container cropping systems project. Results from the first year have shown that 15 of the 34 biobased prototype containers developed by BBRT performed just as well in greenhouse and garden trials as containers made from petroleum-based plastic.

"The objective of phase one was to screen numerous bioplastics and biocomposites for use as sustainable materials that could function as well or better than petroleum plastics for plant containers," said James Schrader, assistant scientist in horticulture and BBRT member.

Plant containers in the Horticulture greenhouse.
Plant containers in the Horticulture greenhouse last spring.

The 34 biobased containers were evaluated alongside conventional petroleum-based plastic containers in the Horticulture greenhouses and in garden trials at the Horticulture Research Station. Research in 2012 evaluated the processability of materials, the performance of prototype containers of each material during greenhouse production, the biodegradation of the materials in soil and the effect of the degrading materials on garden transplants when the container was removed, crushed and buried near the plant roots.

In the greenhouse trials, 11 of the container types that performed well were made of injection-molded bioplastics or biocomposites and four were biobased fiber containers dip-coated with bioplastics. The injection-molded materials evaluated in round one were polymers of soy protein, two commercially available plant starch-based plastics PHA and PLA and composites of PLA and PHA with DDGS or corn stover fillers.

The researchers found that adding biobased filler material to make injection-molded composites improved the processability of the bioplastics during injection molding, increased the rate of biodegradation and reduced the cost of the material required to make the containers without affecting the performance of containers in greenhouse and garden trials.

"One of the best-performing containers during phase one of the project was made of a blended bioplastic that contained 50 percent soy polymer and 50 percent PLA," said Schrader.

He said the blended soy-PLA material developed by BBRT researchers provided a fertilizer effect that improved plant growth and health during greenhouse trials. It also improved plant growth and fruit production during the garden trials with the bioplastic degrading near the plant roots.

James Schrader (left) shows Gowrishanker Srinivasan the root system of one of the plants grown in a PLA container.
James Schrader (left) shows Gowrishanker Srinivasan the root system of one of the plants grown in a PLA container.

Another function of growing plants in soy-PLA containers, Schrader mentioned, is they optimized the growth and structure of the plant roots. "This container has the potential to reduce root circling, a common problem with plants grown in petroleum plastic containers, and may improve transplant establishment in the landscape," he said.

Results of the garden trials demonstrated that transplanting container-grown plants with the container intact on the plant roots slows plant establishment and growth, regardless of the container material. "Based on these results, we will advise potential users of biobased containers to remove the plant from the container during transplanting and break the container into smaller pieces before placing it in the soil to degrade near plant roots," said Schrader.

BBRT researchers have already started work on phase two of the project where they will continue to develop and evaluate 15 to 20 material formulations that have been adjusted based on the results from the first round of greenhouse and garden trials. BBRT researchers Gowrishanker Srinivasan, postdoctoral research associate, and Samy Madbouly, research assistant professor, are leading the materials development and processing portion of the project. The materials will be prepared, extruded and pelletized in the Center for Crops Utilization Research's (CCUR) Technology Transfer Pilot Plant.

Schrader said that all of the injection-molded bioplastics for phase two evaluations will be either blends of two or more biopolymers or composite materials that contain low-cost fillers like DDGS or lignin. "The blends and composites will be designed to combine favorable qualities of different materials that were determined during the 2012 trials," he said.

Researchers will also be adding a second container size to the trials this year. Phase one trials focused on 4.5 inch containers used to produce vegetable plants and herbaceous ornamentals that are ready for transplanting within six weeks. For the second round of trials, researchers will also evaluate the bioplastics for use in gallon-sized containers for growing nursery crops like trees, shrubs and ground covers that remain in containers for longer periods of time.

Trials in 2013 will include similar greenhouse and garden trials to evaluate the suitability of the improved materials for use as replacements for petroleum plastic in plant containers. Schrader and Kenny McCabe, research associate in horticulture, will be leading the greenhouse, garden and biodegradation trials.

The bioplastics container cropping systems project is funded in part by the U.S. Department of Agriculture and led by BBRT faculty members William Graves, professor of horticulture; David Grewell, associate professor of agricultural and biosystems engineering; Michael Kessler, associate professor of materials science and engineering and Schrader.

The BBRT operates under CCUR's research umbrella at Iowa State University.

Using the extruder in the pilot plant
Kenneth McCabe, research associate for horticulture, (right) is extruding a blended bioplastic that contains soy polymer and PLA. Karl Alderks, a student in chemical engineering and member of David Grewell's research team, feeds the extruded plastic into the pelletizer. They are preparing this plastic for the second phase of the bioplastic container cropping systems project.