Date of Award
Master of Science
William R. Graves
Environmental problems caused by petroleum-based plastics have led to interest in alternatives made from biodegradable polymers (bioplastics), but little effort has been made to evaluate horticultural containers made from these materials. Containers were fabricated from polymers of the corn (Zea mays L.) protein, zein. My first objective was to determine the longevity of zein-based containers under conditions typical of horticultural production. Zein containers of two wall thicknesses were filled with either a peat-based, soilless potting substrate or coarse perlite, and they were irrigated every 2 or 4 days. After 10 weeks, weight loss of containers was determined as a measure of their degradation. Containers filled with the peat-based soilless substrate lost nearly twice as much weight as containers filled with perlite, and irrigation every 4 days led to greater weight loss than irrigation every 2 days. In another experiment, to simulate the potential practice of installing plants in the landscape without container removal, bioplastic containers of two sidewall thicknesses were filled with the soilless potting substrate and planted in either drained or saturated field soil, and the two substrates were either sterilized (autoclaved) or nonsterilized. After 12 weeks, containers in drained soils had greater weight loss than containers in saturated soils regardless of substrate sterilization treatment. My second objective was to test the hypothesis that biodegradation of zein-based containers provides nitrogen (N) that promotes growth of geranium (Pelargonium xhortorum L.H. Bail.). Zein containers provided root zones up to 298 and 277 mg·kg-1 NH4+-N and NO3--N, respectively. Unlike plants in conventional plastic containers, leaves of geraniums in zein containers remained dark green when produced without fertilization. Electrical conductivity (EC) and pH of substrate in zein containers increased above ranges recommended for many horticultural crops, and NO2-, which can be toxic to plants, was present in the substrate of zein containers. These chemical changes seem responsible for reduced canopy height and width, leaf area, root system length, and shoot dry weights of geraniums in zein containers compared with geraniums in conventional plastic containers. My third objective was to determine if geraniums grown in zein containers could be transplanted and reestablished successfully with the container intact, thus eliminating the need for disposal of containers. When transplanted with zein containers intact, root and shoot growth of geraniums were reduced until after six weeks, when biodegradation of containers was nearly complete. Migration of roots through the zone of the degraded container and into surrounding substrate was observed approximately three months after transplanting. Our data show the zein-based bioplastic containers we made are suitable for crops having production cycles < 3 months. Geraniums can be produced and transplanted in zein-based containers, but additional research is needed to solve problems that can result from chemical changes to the root zone during production, and from chemical and physical effects on reestablishment after transplant.
Matthew Steven Helgeson
Helgeson, Matthew Steven, "Horticultural evaluation of zein-based bioplastic containers" (2009). Graduate Theses and Dissertations. 10554.