Browsing by Author "Gericke, Willem Adriaan"

Now showing 1 - 1 of 1
  • Thumbnail Image
    Item
    Effects of light manipulation through different photo selected net colours and LEDs (Lactuca Sativa L.) and cabbage as estimated by chlorophyl fluoressence parameters, macro and micro element content and physical measurements.
    (Stellenbosch : Stellenbosch University, 2018-12) Gericke, Willem Adriaan; Le Roux, Marcellous; De Beer-Venter, Misha; Stellenbosch University. Faculty of AgriSciences. Dept. of Agronomy.
    ENGLISH ABSTRACT: Light quantity and quality plays a fundamental role in seed germination, plant growth and development. Plants grown in high radiation regions can experience light stress, resulting in photoinhibition when the photosynthetic capacity of the light harvesting complexes in the photosystems are over-exposed. Shade nets are a cost-effective way to reduce high light quantities and to create a more desirable growing environment. Black shade nets are used widely for vegetable seedling and mature crop production in South Africa, due to its cost effectiveness and availability. Although, recent studies have indicated that coloured shade nets can increase plant responses and physiological processes like seed germination, plant architecture, circadian rhythms as well as plant growth and development. Chlorophyll fluorescence is a non-destructive method used to determine the amount and type of plant stress when a plant is exposed to sub-optimal growing conditions. Unfortunately, no literature could be found to indicate specific chlorophyll fluorescence parameter values, for lettuce and cabbage seedlings and mature crops, grown under different coloured shade nets in high solar radiation environments, and low radiation LEDs. The objective of this study was two-fold. Firstly, to determine the chlorophyll fluorescence parameters for lettuce and cabbage seedlings and mature plants produced under different coloured shade nets with high solar radiation, and the leaf macro- and micro-element composition of lettuce and cabbage seedlings and mature plants, and physical analyses of mature cabbage plants. Secondly, to determine chlorophyll fluorescence parameters, and leaf macro- and micro-element composition of lettuce seedlings, under different colour combination low radiation LEDs. The research was conducted by means of three replicates of five different coloured shade nets – with the black net as the control. ‘Grand Slam’ and ‘Islandia’ lettuce, and ‘Conquistador’ and ‘Sapphire’ cabbage cultivars were grown under each high solar radiation coloured net. The second trial entailed where ‘Robinson’, ‘Grand Slam’, ‘Lolla Rossa’ and ‘Multi Red’ lettuce seedlings were grown under high radiation under the same coloured shade nets and were compared to different LED combinations of low radiation. An analysis of variance (ANOVA) was used for data analysis, and Fisher’s least significant differences were used to determine the mean data comparisons. Dark pigmented lettuce had higher RC/ABS values than green lettuce, and these values differed statistically per cultivar. The RC/ABS values did not differ between the B+DR and B+FR LEDs, although they were significantly lower than under the coloured shade nets. The PItotal values decreased after head formation and this indicates decreasing PN values. All chlorophyll fluorescence parameters were greatly influenced by plant age. The OJIP transient curve is indicative of P levels in lettuce. The largest P uptake differences between lettuce cultivars were under Photon Red and white nets - while the blue nets produced the least variance for P uptake in different lettuce cultivars. All macro- and micro-element uptake for lettuce seedlings was significantly higher under the low radiation B+DR LEDs than different coloured shade nets under high solar radiation. The B+DR LEDs vastly increased the uptake of Cu, followed by Na, Zn, Ca Cabbages grown under white nets averaged 8.16 kg, and were 86% heavier than cabbages produced under black nets. Cabbage leaf length and width values were significantly higher under white nets. Also, it produced the lowest N, P and K leaf levels under the Photon Red and white nets, while cabbages under the black nets had the shortest and narrowest leaves - but the highest N, P and K values. The blue nets once again produced the smallest variance regarding the uptake ratio of N, P and K for the different cabbage cultivars.