Evaluation of Biopolymer-coated Fiber Containers for Container-grown Plants

Abstract

Biocontainers made of coconut coir, paper, peat, wood, or other natural fibers are considered sustainable alternatives to containers made of petroleum-based plastics, but growers’ acceptance and use of fiber containers have been limited by their comparatively high cost, low strength and durability, and poor water-use efficiency (WUE). We hypothesized that coating fiber containers with biopolymers would improve their strength, durability, and WUE during plant production. We compared the effectiveness of fiber containers of coir, paper, and wood that were either uncoated or coated with one of four biopolymers [polyamide (PA), polylactic acid (PLA), polyurethane (PU), or tung oil (TO)], peat-fiber containers that were uncoated, and injection-molded containers made of petroleum-based plastic. Ease of coating was assessed, along with the cost and strength of containers, their effectiveness during greenhouse production of ‘Honeycomb’ marigold (Tagetes patula), ‘Autumn Bell’ pepper (Capisicum annuum), ‘Madness Red’ petunia (Petunia ×hybrida), ‘St. John’s Fire’ salvia (Salvia splendens), and ‘Rutgers’ tomato (Solanum lycopersicum), and their WUE during production of salvia and tomato. Castor oil-based PU was the least expensive biopolymer coating and was easy to apply as a water-based dispersion. The other biopolymers required a hazardous and costly organic solvent (e.g., chloroform). Coatings of PA, PLA, and PU increased container strength and durability, and improved WUE during plant production. Coated paper-fiber containers resisted horizontal compression better than petroleum-plastic containers. Greenhouse-grown plants in containers coated with PA, PLA, or PU were larger and rated healthier and of better quality than plants grown in uncoated or TO-coated fiber containers. Plants grown in paper- and coir-fiber containers coated with PA, PLA, or PU were similar in health and size to plants grown in petroleum-plastic containers. Two coatings of PU on paper-fiber containers resulted in WUE similar to that of petroleum-plastic containers for both 4- to 5-inch and gallon sizes. Coating fiber containers with biopolymers slowed, but did not halt, their degradation in soil, indicating that decomposition in soil may be a suitable end-of-life option for biopolymer-coated fiber containers. Our results support the hypothesis that coating fiber containers with biopolymers can improve their effectiveness for crop production, while maintaining an improvement in sustainability over petroleum plastic. Paper-fiber containers coated with PU showed particular promise and were similar in material cost and performance to containers made of petroleum-based plastic.