Thesis(Ph.D. Agriculture (Soil Science)) -- University of Limpopo, 2020 / Due to high incidents of drought in the semi-arid regions of Limpopo Province, South
Africa, the potential feasibility of using treated wastewater for irrigating vegetable crops
had been researched and developed under the best practices of Natuurboerdery
farming system. The investigation aimed at the development of soil and plant health
management strategies for crops irrigated with treated wastewater that could
ameliorate the ever-increasing demand for fresh irrigation water in the Province.
Seven specific objectives, reduced to three overall objectives under Natuurboedery
farming system were intended to investigate (1) the chemical and biological quality of
treated wastewater used in irrigation with respect to disposal points and sampling
period, (2) the responses of soil physico-chemical properties, heavy metal distribution
and biological-soil-health indicators to irrigation with treated wastewater under field
conditions and (3) the partitioning of cations and heavy metals in root, stem and leaf
tissues of onion, tomato and a selected weed plant irrigated with treated wastewater.
In each objective, unless otherwise stated, treatment effects were described at the
probability level of 5%. In Objective 1, relative to the borehole water, treated
wastewater had lower concentration of Ca, Mg, K, Na, Cl, HCO3
-
, SO4
-
, Zn, Cr and Pb,
with temporal and spatial tendencies in accumulation of certain elements. In contrast,
the treated wastewater had higher loads of pathogenic microbes that included bacteria
(Escherichia coli, Salmonella spp., Shigella spp. and Vibrio spp.), protozoa
(Entamoeba histolytica) and two helminths (Schistosoma mansoni; Ascaris
lumbricoides), with temporal and spatial tendencies. In Objective 2, Al and Cr tended
to be high in deeper soil layers (60-100 cm), whereas most essential nutrient elements
and essential heavy metals (Cu, Fe, Mn, Ni, Zn, As, Cr and Pb) were contained in the
upper soil levels (0-40 cm). The upper soil levels were also characterised by having
substantial attributes of root health, namely, soil organic carbon, active carbon and
potentially mineralisable nitrogen. In Objective 3, root, stem and leaf tissues of
horseweed (Conyza canadensis L.), onion (Allium cepa L.) and tomato (Solanum
lycopersicum L.) plants had different accumulation abilities for different metals, except
for As. Contrary to the expectation, the onion bulb contained less test cations and
heavy metals. In conclusion, in terms of chemical component at the time of sampling,
as depicted from the water and soil samples, the treated wastewater was suitable for
irrigation. However, in terms of pathogenic microbes, the treated wastewater was not
suitable for irrigating crops intended for human consumption due to significantly higher
loads than the permissible standards. Amongst all observed challenges, the reduction
of pathogenic microbes should be given priority since it contravened existing national
and international standards for using treated wastewater for in irrigation of crops
intended for human consumption. / National Research Foundation (NRF)
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ul/oai:ulspace.ul.ac.za:10386/3962 |
| Date | January 2020 |
| Creators | Kgopa, Pholosho Mmateko |
| Contributors | Mashela, P. W., Manyevere, A. |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | xxv, 256 leaves |
| Relation |
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