Author Identifiers

Jacqualine Thomas
ORCID: 0000-0001-7058-4687

Date of Award

2020

Degree Type

Thesis

Degree Name

Master of Science by Research

School

School of Science

First Advisor

Professor Kamal Alameh

Second Advisor

Dr Mikhail Vasiliev

Abstract

With the increase in world population, the continued advances in modern greenhouse agriculture and plant growth practices are expected to help overcome the global problem of future food shortages. This research investigates a way to assist in stemming the problem of food shortage by using optimised light irradiation (within the constraints of the experiment) on a sample plant species of lettuce (Lactuca sativa, L.). Whilst lettuce is often grown in hydroponic systems, the current research is conducted in stand-alone pots with hand watering, due to the requirements of health and safety and available resources.

The experiments were designed such that firstly a sample of 30 lettuce plants in three different grow tents, having a separate light treatment in each tent (white visible light in Tent 1; red and blue visible light in Tent 2; and red, blue and far-red visible light in Tent 3), totalling 90 lettuce plants, grown for 39 days. The plants were then culled and the wet weight and dry weight of the above-ground parts of the plants were measured, and the biomass of each individual plant determined. The results were then utilised to inform which of the three light treatments provided the ‘optimum’ biomass results for the lettuce plants, that being the red, blue and far-red visible light treatment. From identifying the optimum biomass producing light treatment, a model of a thin-film filter, which transmits the visible light in the red, blue and far-red visible regions and filters all other radiation was designed, using the Opti-Layer Pro program. The experimental results show that substantial biomass productivity improvements in the lettuce (up to approximately 14.7%) can be attained by using spectrally optimized illumination, instead of white light illumination.

The resultant 9-layer thin-film filter was then fabricated in ESRI’s Clean Room using the E-Beam Evaporation system, with a balanced and symmetrical combination of ZnS, Al2O3 and Ag. It was then demonstrated that the fabricated thin-film filter could reproduce, when exposed to sunlight, very similar transmission output to the optimum LED spectrum that maximised the biomass in the grow tents. This paves the way for offering viable solutions to greenhouse operators wanting to utilise glass, instead of short-lifetime plastic coverings, to coat their glass with thin-film coatings that pass the optimal wavelengths that maximise the crop yield.

In the work to be conducted in the future, other plant species such as basil, tomatoes and capsicums can be investigated to determine their optimum biomass and other parameters, such as the wet and dry root masses, the nutritional quality of the plants produced, their chlorophyll content, which define the plant quality. This also opens the possibility for thin-film filters to be applied to sections of the greenhouse so that more than one plant species can be optimally grown, simultaneously.

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