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The effect of different potassium concentrations and electrical conductivity on hydroponic- grown Trachyandra divaricata, as a green vegetable
Author(s)
Bulawa, Bakholise
Date Issued
2023
Type
Thesis
Publisher
Cape Peninsula University of Technology
Abstract
The shortages of freshwater supply, inadequate groundwater, and high salinization levels in
soil have become major challenges worldwide. Salinization, which refers to the presence of
salts in the soil or water, is a common challenge in half of cultivated soil in South Africa and
that makes it difficult for conventional crops to absorb nutrients and water. However, the
salinity phenomenon has hampered the quality of arable soil and promoted the use of lowquality
water (brackish or saline water) due to the lack of fresh water. Saline water has proved
to harm the quality of crops and soil as it encourages soil erosion and causes a decline in soil
nutrients for plants. This problem has facilitated the consideration in cultivation of coastal
plants as potential alternatives as they are naturally evolved salt-tolerant species that can
survive in a saline environment. Trachyandra divaricata is an indigenous coastal plant native
to the southern African region and distributed in this hot and dry Mediterranean type climate
and in high saline conditions along the coast. Trachyandra divaricata flower buds were
historically harvested in coastal regions by indigenous people and eaten raw or boiled as a
nutritious inflorescent vegetable. However, there has been insufficient scientific
documentation supporting biochemical properties and nutritional content of this plant besides
the knowledge collected from indigenous people. Cultivating this plant in hydroponics could
be efficient as it will utilise minimal resources and nutrients but cutting plants back to
encourage new growth.
This aim of this study was to investigate the nutrient profile, antioxidants potential, and flower
bud development of the hydroponically grown T. divaricata in reaction to different potassium
dosages and levels of cutting heights to discover the appropriate protocol of the plant in a
hydroponic system. Four identically constructed Nutrient Film Technique (NFT) systems
arranged in a complete block design were used, with each system on a separate metal mesh
steel table (900 mm x 1 250 x 25000 m) having 10 replicates of each treatment. Nutrifeed™
was used as a basic nutrient in all systems, however, different potassium concentrations
(0.0216, 0.0144 and 0.0072 M of K2SO4) were used as treatments added in into each sump,
while the system with Nutrifeed only considered as a control. The different treatments
comprised of plants with three different cutting height levels and non- cut plants considered
as control, 5 cm (minimal), 10 cm (moderate) and 15 cm (maximum cutting). The plant height
was measured using a standard ruler and the number of flower buds counted manually during
and after experiment. A laboratory scale was used to measure fresh and dry weight of the
plant. SPAD-502 Konic-Minolta meter was used to measure the chlorophyll content of the
plants. The phytochemicals and antioxidants were analysed using dried samples of flower
buds by means of assays for total flavonols, total polyphenols, 2,2'-azinobis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), ferric reducing antioxidant power (FRAP), and 2,2-diphenyl-1-picrylhydrazyl (DPPH). Similarly to nutrient contents and proximate analysis, the dried flower buds were assessed by means of assays for carbohydrates, crude proteins, crude fat content, Ash content, moisture content, Non fiber carbohydrates (NFC), Neutral detergent fibre (NDF), energy content, macro-elements (( sodium (Na), phosphorus (P),
magnesium (Mn), potassium (K and nitrogen (N)) and micro nutrients (Magnesium (Mn), Zinc
(Zn), Cupper (Cu) and Iron (Fe)). The plants irrigated with 0.0072 M of K2SO4 without pruning
showed a substantial improvement in floral bud, Neutral detergent fiber, fresh and dry weight
of the shoots and roots, ash, as well as height. Contrarily, calcium and chlorophyll content
were equivalent among treatments, but the treatment 0.0114 M of K2SO4, and 10 cm of pruning
produced the maximum production of nitrogen, sodium, potassium and Zinc. The plants that
were pruned by 10 cm and irrigated with 0.0072 M of K2SO4 had the maximum antioxidant
value (Flavonol, DPPH and Polyphenols). The results suggest that T. divaricata is a viable
leafy vegetable since a minimal concentration of K2SO4 (0.0072 M) and moderate cutting back
the plants optimized its productivity in relation to the biomass characteristics, growth,
antioxidant potential and nutritional content.
soil have become major challenges worldwide. Salinization, which refers to the presence of
salts in the soil or water, is a common challenge in half of cultivated soil in South Africa and
that makes it difficult for conventional crops to absorb nutrients and water. However, the
salinity phenomenon has hampered the quality of arable soil and promoted the use of lowquality
water (brackish or saline water) due to the lack of fresh water. Saline water has proved
to harm the quality of crops and soil as it encourages soil erosion and causes a decline in soil
nutrients for plants. This problem has facilitated the consideration in cultivation of coastal
plants as potential alternatives as they are naturally evolved salt-tolerant species that can
survive in a saline environment. Trachyandra divaricata is an indigenous coastal plant native
to the southern African region and distributed in this hot and dry Mediterranean type climate
and in high saline conditions along the coast. Trachyandra divaricata flower buds were
historically harvested in coastal regions by indigenous people and eaten raw or boiled as a
nutritious inflorescent vegetable. However, there has been insufficient scientific
documentation supporting biochemical properties and nutritional content of this plant besides
the knowledge collected from indigenous people. Cultivating this plant in hydroponics could
be efficient as it will utilise minimal resources and nutrients but cutting plants back to
encourage new growth.
This aim of this study was to investigate the nutrient profile, antioxidants potential, and flower
bud development of the hydroponically grown T. divaricata in reaction to different potassium
dosages and levels of cutting heights to discover the appropriate protocol of the plant in a
hydroponic system. Four identically constructed Nutrient Film Technique (NFT) systems
arranged in a complete block design were used, with each system on a separate metal mesh
steel table (900 mm x 1 250 x 25000 m) having 10 replicates of each treatment. Nutrifeed™
was used as a basic nutrient in all systems, however, different potassium concentrations
(0.0216, 0.0144 and 0.0072 M of K2SO4) were used as treatments added in into each sump,
while the system with Nutrifeed only considered as a control. The different treatments
comprised of plants with three different cutting height levels and non- cut plants considered
as control, 5 cm (minimal), 10 cm (moderate) and 15 cm (maximum cutting). The plant height
was measured using a standard ruler and the number of flower buds counted manually during
and after experiment. A laboratory scale was used to measure fresh and dry weight of the
plant. SPAD-502 Konic-Minolta meter was used to measure the chlorophyll content of the
plants. The phytochemicals and antioxidants were analysed using dried samples of flower
buds by means of assays for total flavonols, total polyphenols, 2,2'-azinobis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), ferric reducing antioxidant power (FRAP), and 2,2-diphenyl-1-picrylhydrazyl (DPPH). Similarly to nutrient contents and proximate analysis, the dried flower buds were assessed by means of assays for carbohydrates, crude proteins, crude fat content, Ash content, moisture content, Non fiber carbohydrates (NFC), Neutral detergent fibre (NDF), energy content, macro-elements (( sodium (Na), phosphorus (P),
magnesium (Mn), potassium (K and nitrogen (N)) and micro nutrients (Magnesium (Mn), Zinc
(Zn), Cupper (Cu) and Iron (Fe)). The plants irrigated with 0.0072 M of K2SO4 without pruning
showed a substantial improvement in floral bud, Neutral detergent fiber, fresh and dry weight
of the shoots and roots, ash, as well as height. Contrarily, calcium and chlorophyll content
were equivalent among treatments, but the treatment 0.0114 M of K2SO4, and 10 cm of pruning
produced the maximum production of nitrogen, sodium, potassium and Zinc. The plants that
were pruned by 10 cm and irrigated with 0.0072 M of K2SO4 had the maximum antioxidant
value (Flavonol, DPPH and Polyphenols). The results suggest that T. divaricata is a viable
leafy vegetable since a minimal concentration of K2SO4 (0.0072 M) and moderate cutting back
the plants optimized its productivity in relation to the biomass characteristics, growth,
antioxidant potential and nutritional content.
Additional information
Thesis (Master of Horticultural Science)--Cape Peninsula University of Technology, 2023
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