Browsing Department of Horticulture by browse.metadata.advisor "Combrink, N. J. J."
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- ItemGreenhouse production of watermelon (Citrullus lanatus)(Stellenbosch : Stellenbosch University, 2005-03) Kuvare, Uparura S. K. (Uparuru Silvanus Karl); Combrink, N. J. J.; Stellenbosch University. Faculty of AgriSciences. Dept. of Horticulture.ENGLISH ABSTRACT: Various researchers have determined that salinity causes several kinds of damage to plants such as germination inhibition, metabolic disturbances, yield reduction and quality losses. However, the severity of salt damage has been found to be dependent on the cultivar, level of salinity, period of exposure to salinity, and the growth stage of the plant. An understanding of the severity of salinity and its potential negative impacts on crops is essential to optimise production. Knowledge of seed vigour, expressed as germination percentage and germination rate at the optimum temperature for germination, would provide growers with valuable information to measure and compare the viability of seed lots. A study was done where fresh and aged seeds of two watermelon cultivars were investigated in germination tests under laboratory conditions at four salinity levels and five temperature regimes. The best germination was achieved at 4 mS cm-1 for both cultivars, Odem and Paladin. At 8 mS cm-I, the germination percentage for Paladin was 31% better than for Odem. The germination time for aged Odem seeds was significantly delayed at this EC 8 level but ageing of Paladin seeds had no detrimental effect at this EC level. Paladin germinated significantly better than Odem at the relatively low temperature range of I5-20°C, indicating that it is well-adapted for early planting. A new plant growing system, using vertical training of two shoots was tested in a greenhouse, aiming to optimise the growth regulating capabilities of this crop environment. Traditional watermelons are open-field planted in rows at low densities. Even with this plant spacing, by harvesting time the vines are spread in such a way that the foliage laterally covers the inter-row spacing, making cultivation practices such as spraying, weeding and harvesting difficult and almost impossible. The production of greenhouse crops is advantageous, but involves a number of cultural inputs and techniques for optimum yields. The effects of plant pruning systems and salinity levels on watermelon cultivars (Odem and Paladin) in a low-cost greenhouse were studied using a drain-to-waste fertigation system. Changing the nutrient solution from a low salinity level (EC 4 mS cm1) during vegetative growth to EC 4 mS cm-I after pollination, did not reduce fruit mass, but significantly increased the sugar yield of Odem, the icebox-type cultivar. Excessive pruning (less leaves per shoot) was more efficient with low salinity levels than at a high salinity level. Moderate pruning (more leaves per shoot) represented a good system, producing fruits of lesser weight and acceptable quality.
- ItemGrowth, development and nutritional value of Amaranthus tricolor L. as affected by salinity and harvesting procedure(Stellenbosch : Stellenbosch University, 2004-03) Ribeiro, J. E. M. M. (Jeronimo Ernesto Meneses Machado); Combrink, N. J. J.; Stellenbosch University. Faculty of AgriSciences. Dept. of Horticulture.ENGLISH ABSTRACT: Low crop productivity in arid and semi-arid regions is a problem caused by water stress as well as associated high levels of soil and water salinity. An increased demand for salt tolerant crops is experienced in these regions. Amaranth is a glycophyte and C4 dicotyledonous crop, well adapted to arid and semi-arid regions. Previous studies on the physiological response of salt-stressed amaranths have indicated that this crop is salt tolerant. As vegetable, amaranths can be harvested by uprooting and by topping. The most common harvesting method is by topping, allowing repeated harvesting. When harvested by topping, the cutting height is an important parameter that may be manipulated to optimise growth rates. In this study, plants were exposed to different salt stress levels and harvesting procedures while yield and quality of Amaranthus tricolor were investigated. Nutrient solutions at four different electrical conducti vi ty (EC) levels were used to fertigate the plants. At high EC levels (4 mS cm-l and 8 mS cm-lj, the length and diameter of main stems, internode lengths, stem weights as well as root weights were reduced, especially with a longer growth period. However, the shoot: root ratio and leaf protein yields increased and flowering was delayed. The best leaf yield was obtained where plants were fertigated at an EC of 4 mS cm-l for 45 days. The cutting height did not affect leaf yield, growth rates and leaf protein yield in plants fertigated at EC levels of 1, 2 and 4 mS cm-l. At an EC of 8 mS cm-l, the growth rate recovered to a value similar to that of plants fertigated with an EC of 2 mS cmonly where plants were topped at 25%. With this less destructive cutting height (topped at 25%), leaf yields, growth rates and ·leaf calcium and protein yields at an EC of 8 mS cm" were superior to that of plants topped at 50%. In plants topped at 25%, the recovered growth rates at EC 8 mS cm-l was probably due to more photosynthetic active tissue left after cuttings, resulting in the accumulation of compatible solutes for osmotic adjustment.