Doctoral Degrees (Agronomy)

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Browsing Doctoral Degrees (Agronomy) by browse.metadata.advisor "Famba, Sebastiao"

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    Optimizing harvesting procedures of Amaranthus hybridus L. and A. tricolor L. under different watering regimes during hot and cool seasons in southern Mozambique
    (Stellenbosch : Stellenbosch University, 2017-03) Ribeiro, Jeronimo E. M. M.; Pieterse, P. J.; Famba, Sebastiao; Stellenbosch University. Faculty of AgriSciences. Dept. of Agronomy.
    ENGLISH ABSTRACT: Drought has been the major constraint for vegetable and food crop production in arid and semi-arid regions as is the case in southern Mozambique with a tropical dry savanna climate that is prone to droughts. In this vulnerable region, malnutrition associated with scarcity of vegetables imposed a serious constraint in the diet of rural communities. Rural communities are forced to use wild plants, such as amaranth, as a way to supplement their nutrition. Here Amaranth species grow naturally and the leaves are regularly collected manually to be consumed as tender greens. There is no evidence of grain consumption. Although few growers cultivate amaranth in small areas or in their gardens, the intensity and frequency with which the leaves are collected has not been tested yet. The production of multi-purpose amaranth, a C4 plant widely distributed in the tropics and relatively drought-tolerant crop, offer a great potential to play a beneficial role in nutrition and food security. Three field experiments with Amaranthus hybridus and A. tricolor repeated six times each (three during the rainy season and three in the dry season) were carried out during the period from December 2013 to October 2015 in Maputo. A randomized complete block design in a factorial arrangement was used in each experiment. Experiment one aimed to assess the vegetative growth, flowering, leaf and grain yields, as well as nutrient contents in leaves and grain of those species when subjected to watering regimes of 80%, 50% and 20% of total available water. The relationship between temperature and day length on the leaf yield and the time to flowering were also assessed (Chapters 3 and 4). The treatments were laid out in a 3 x 2 factorial arrangement with six replications. In experiments two (Chapther 5) and three (Chapter 6), under the same watering regimes and with the same species, the vegetative growth, leaf yield and nutrient content were assessed as affected by harvesting intensity (plants topped by 25% and 50% of their heights) and harvesting frequency (every two weeks and every three weeks) respectively. In these two experiments, the treatments were laid out in a 3 x 2 x 2 factorial arrangement with three replications. Results from experiment one revealed that vegetative and reproductive growths were sensitive to soil water contents of 50% and 20% of total available water. However, the vegetative growth was less susceptible to water deficits that occurred in short intervals throughout the rainy season. Higher calcium and crude protein contents in the leaves were found at low water levels with the highest values obtained in A. tricolor. Temperature significantly affected the high leaf yield during the rainy season while day length had a noticeable influence on the low leaf yield during the dry season. The onset of flowering was determined by day length and minimum temperature with day length the most determining factor. The vegetative growth of both species showed similar behavior in response to different soil water and climate conditions over the year. The highest grain yield and harvest index was obtained in A. tricolor with an increase in minimum temperature which delayed flowering mainly when the day length was above 12 hours day-1 during the rainy season. The results from experiment two and three indicated insufficient evidence to support the hypothesis that the combined effects of watering regimes and harvesting intensity, and watering regimes and harvesting frequency affect vegetative growth in both species. However, the vegetative growth of both species was tolerant to water deficit at 50% of total available water with successive cuttings. The best harvesting intensity and frequency found was 25% of their heights and two-week intervals respectively, since this frequency yielded more small and tender green leaves which are preferred by the consumer. Amaranthus hybridus showed better performance and higher leaf yield compared to A. tricolor over the year. Results also revealed that the multiple harvests extend the vegetative growth phase which is an advantage for amaranth leaf production, especially under short days during the dry season. In plants harvested several times, the calcium and crude protein were not affected by watering regimes. However, the highest calcium and crude protein content in the leaves were obtained at final and first harvests respectively. As a leafy vegetable, A. hybridus showed to have potential to become a suitable crop throughout the year and to supplement calcium and protein requirements in the diet of rural communities. It is recommended to be cultivated in the rainy season under rain-fed condition with supplemental irrigation and in the dry season as an irrigated crop at 50% of total available water. In both seasons, the leaf harvesting should be topping by 25% at 2 weeks intervals.