Doctoral Degrees (Agronomy)

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Browsing Doctoral Degrees (Agronomy) by browse.metadata.advisor "Kempen, Estelle"

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    Influence of nutrient and light management on postharvest quality of lettuce (Lactuca sativa L.) in soilless production systems.
    (Stellenbosch : Stellenbosch University, 2017-03) Mandizvidza, Tonderai Clive; Kempen, Estelle; Stellenbosch University. Faculty of AgriSciences. Dept. of Agronomy.
    ENGLISH ABSTRACT: Despite the ease in manipulating plant growth and development variables, meticulous management is required to achieve high yields and good quality crops in a soilless system. A deep understanding of the intricacies involved in plant growth and development will aid in optimizing these variables to achieve desired yield and crop quality with subsequent effect on postharvest quality. Therefore manipulating and managing plant growth and development variables should be considered as pivotal in a soilless production system. For that reason, other techniques such as foliar fertilization have been employed in an attempt to enhance crop growth and development during production to increase productivity and crop quality. The aim of this study was to assess how manipulation and management of nutrient solutions (different cation concentrations), light intensity levels and foliar fertilization in a hydroponic system affect postharvest quality. The study on nutrient cation concentrations was conducted in a tunnel whilst light intensity study was conducted in a controlled glasshouse at the University of Stellenbosch in the Western Cape Province of South Africa. To evaluate the effect of light intensity levels, two lettuce types (cos and iceberg) were exposed to three different light intensities, control of 450 μmol m-²s-1 (19.44 mol m-²d-1), 60% of control at 270 μmol m-²s-1 (11.66 m-²d-1), 40% of control at 180μmol m-²s-1 (7.78 m-²d-1). Overall visual appearance was considered using plant height (mm) and cos lettuce reaching significant height at 60% and 40% LI. A significant interaction was observed with regards to texture parameter with cos lettuce generally outperforming iceberg. In the second trial, nutrient solutions with different cation concentrations were evaluated. Two lettuce types (cos and iceberg) were cultivated hydroponically with nutrient solutions containing Ca⁺² as 45% of the total cations (S 1) compared to low Ca⁺² of 20% of the total cations (S 2) and high Ca⁺² of 60% of the total cations (S 3) all at an EC of 1.30 mS cm-1. Based on the nutrient composition, the increase or decrease in cation concentration affected the uptake of nutrients with adverse effects on nutritional values of crops. Variation was largely due to nutrient availability at different concentrations for plant absorption and use. Lastly, foliar fertilization of Ca based boron, nitrogen and silicate sprays on rocket and red oak lettuce revealed interactions between the foliar treatments (CaN, CaB and CaSi) and plant types (red oak lettuce and rocket) on the fresh weight (yield) of plants grown hydroponically and differences in means with regard to total moisture and weight loss were also observed for treatment and crop variety effect. The results in this thesis make a valuable contribution to our understanding of manipulating and management of soilless production system with adverse effects on postharvest.