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Sustainable vegetable greenhouse production through bio-conversion of greenhouse solid wastes and re-utilization Cheuk, William Wai Lun

Abstract

Current practices of handling greenhouse wastes are not the sustainable ways to conserve agricultural lands and ground waters. This study developed a sustainable growing practice in the vegetable greenhouse industry. Waste handling (shredding) and the biodegradable plastics were investigated first. Then, different composting control algorithms and substrate recipes were tested in both lab scale and pilot scale composting. With a good control algorithm, composting of greenhouse wastes could reach the requirement for Process to Reduce Further Pathogens, PFRP (55 OC for 3 days). Ammonia emission might be a problem but it could be reduced by using air-recirculation or removed by a biofilter with compost as medium. Recirculation cooling control was found to be a more effective method, to maintain the process temperature below the set point, than any kind of temperature feedback control. Less leachate and condensate were found from the reactors with air recirculation control. Systems with air recirculation for cooling and aeration showed higher degradation rates, and also more consistent moisture content of the final compost. Alder bark was found out to be a better choice of bulking agent than hemlock bark in terms of better substrate structure, more carbon loss, less nitrogen loss, and higher process temperature. Shredding was proven to be not necessary before composting of prunings and it also helped minimizing the amount of leachate. Bulking agents (alder bark) of about 20-30% (in weight) were found necessary for composting prunings. For year-end wastes, a ratio of 62% vines, 13% used sawdust and 25% alder bark was recommended for in-vessel composting. Using conventional management techniques in greenhouse tomatoes, a similar yield using a 2:1 sawdust to amendment mix by could be achieved compared to conventional sawdust medium. Significant reduction of crown and root rot disease caused by Fusarium oxysporum f. sp. radicis- lycopersici in susceptible tomatoes was achieved by addition of the greenhouse compost amendment to seedling plugs or blocks, and by mixing with the sawdust medium. A mixture of 2:1 sawdust to amendment by volume was shown to be effective. The reduction in disease resulted in 74% improved yield over a full growing season under high disease pressure.

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