Use of plastic bottles as an alternative container type for propagation of forest tree seedlings in restoration programs
Deforestation and forest degradation is a global issue, especially in poor and developing regions of the world. In order to combat deforestation it is critical to enhance the productivity of forest restoration operations, which often involve planting of nursery-grown forest tree seedlings. Production of low quality stock types with deformed and spiraled root systems is a significant issue hindering successful restoration programs. Polybags (i.e., small plastic bags) are a common container type for seedling propagation in developing countries. However, polybags produce seedlings with spiraled and deformed root systems that reduce outplanting survival and performance. Use of discarded plastic water bottles could be a feasible alternative as a container type for seedling propagation in restoration programs. The overall objective of this study was to develop technology for repurposing discarded plastic beverage bottles to grow quality native plants, trees and shrubs to benefit agroforestry, reforestation, restoration, and conservation programs. Specific objectives for this study were accomplished in two separate experiments (CHAPTER 2): 1) Container Comparison Experiment - to compare root and shoot development of seedlings grown in plastic bottles, modern nursery containers, and polybags; and 2) Bottle Modification Experiment - to examine the effects of root spiraling control techniques and container opacity on seedling morphological attributes. In the Container Comparison experiment, seedlings of two species, Afghan pine (Pinus eldarica Medw.) and Arizona walnut ( Juglans major [Toor.] Heller), were grown in four container types; Coca-Cola® beverage bottle (Coke), modern container Deepot™ D27 (D27), Polyethylene polybag (polybag), and Sam's Club® water bottle (Sams). At the first sampling period in August, Arizona walnut seedling shoot height, shoot dry biomass, and root dry biomass were all significantly greater in D27 containers compared to Coke bottles and polybags, while Sams bottles did not differ among treatments. Afghan pine seedling shoot height was significantly greater for seedlings grown in the Sams bottles compared to polybags, while Coke bottles and D27 did not differ among treatments. Root fibrosity was greater for seedlings grown in both Coke and Sams bottles compared to D27 and polybags. Similarly, the number of lateral roots was greater in Coke bottles compared to D27 and polybag containers. At the final measurement period (November), significant differences among treatments were found for all root morphological responses; for both species, seedlings grown in plastic bottles and modern containers had significantly less spiraled roots compared to the polybag. Seedling shoot and root development in plastic bottles at the end of the growing season was equal to or greater than that of the modern container. First year field height and diameter of Arizona walnut and Afghan pine were similar among containers. Similarly, first year field survival of both species was not affected by container type and was 100% for both species. In the Bottle Modification experiment, Afghan pine seedlings were grown in Coca-Cola® beverage bottle with three opacity levels (green, black, and clear) and three spiraling control methods (side-slits, internal-ridges, and control). There were no significant interactions between spiral prevention and opacity treatments except for algae growth inside the container walls; black containers with either of the spiral control treatments produced lower algae fresh weight compared to clear and green containers. Spiral control treatments had significant impacts on Afghan pine RCD; Side-slit containers produced greater RCD compare to control and internal ridge containers. Side-slit and internal-ridge containers produced significantly lower numbers of spiraled roots compared to control (solid-wall) containers. At the beginning of the growing season, container opacity had significant impacts on seedling shoot height; green and clear containers produced significantly taller shoots compared to black. At the end of the growing season, black containers produced seedlings with significantly more fibrous roots compared to green containers, but no differences were detected in comparison to clear bottles. There were no significant interactions between spiral prevention and opacity treatments for first year field height and diameter growth. Individually, both spiral prevention and opacity treatments had no significant influences on Afghan pine field height and diameter excepting opacity for height growth. Green containers produced seedlings with significantly greater field diameter than black, while clear was not different among them. Based on this research, plastic bottle containers may provide an effective alternative for production of high quality seedlings; use of side-slits represents a feasible way to prevent root spiraling. Future research should examine alternative media types from locally available resources and the growth of a variety of native species in these bottle container types.
Jacobs, Purdue University.
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