The 2012 ASHS Annual Conference

An obstacle to sustainability in the container-crops industry is the nearly universal reliance on containers made from non-renewable, petroleum-based plastics.  As part of a project to develop and assess biodegradable plastics for their potential to replace petroleum-based plastics in specialty-crop containers, we evaluated prototype plastic containers made from soy (Glycine) protein for their effectiveness during production of plants in greenhouses and subsequent establishment of those plants outdoors.  Our objective was to assess the function and biodegradation of soy-plastic containers during production and transplant establishment, with special attention to whether a fertilizer effect results from degrading containers before and after plants are installed in gardens.  Plants of tomato (Lycopersicon) and pepper (Capsicum) were grown in soy-plastic containers and control containers of petroleum-based (polypropylene) plastic under greenhouse conditions for four weeks.  The plants then were transplanted and grown in a garden plot for five weeks with containers removed and broken to pieces < 4 cm long that were dispersed beneath roots of the transplant.  At the end of greenhouse production, durability ratings were greater for control containers compared to soy-plastic containers, and plants grown in control containers were larger, greener (SPAD), and rated healthier than plants grown in soy-plastic containers.  Measures of pH and EC of leachate suggest that the fertilizer effect from degradation of soy-based containers during plant production was excessive and decreased plant growth and health compared to controls.  Growth and health of plants produced in soy-plastic containers improved during establishment in gardens with pieces of the containers degrading near roots.  After five weeks of garden culture, plants of tomatoes produced in soy-plastic containers were larger and greener than controls, with no difference in health rating.  Plants of pepper produced in soy-plastic containers were greener and healthier, but remained smaller, than controls.  Average biodegradation during five weeks in the garden was 59% for soy-plastic containers and 0% for polypropylene containers.  Although the design and material formulation of soy-plastic containers need to be improved to sustain container integrity and plant health during production, the establishment in gardens of plants produced in soy-based containers was promising.  Post-production fertilizer effects during biodegradation of soy-plastic containers appear beneficial, and the rate of biodegradation in garden soil was favorable for establishment of transplants.