This study was conducted in Soutloop River Catchment, Northern Cape, South Africa. Although hydrologic models play a critical role in the management of natural resources in arid areas, their application is challenged by the scarcity of data for calibration and validation. Therefore, this study aimed at to configure, calibrate and validate SWAT model in a data-scarce catchment by using the regionalization with physical similarity approach. This approach uses dual calibration and validation procedure, i.e., one in the donor catchment (by using SWAT-CUP (SWAT Calibration and Uncertainty Programs) and the other on the study catchment (by manual calibration and verification). Based on the sensitivity analysis, sixteen parameters were calibrated by SWAT-CUP. The result from the uncertainty analysis indicated acceptable values of both the R-factor (0.8**) and P-factor (0.7**). The model performance evaluation also showed acceptable ranges of values (e.g., NS was 0.76** and R2 was 0.78**). However, the main calibration and validation process was conducted outside the target catchment, though it was assumed that the donor and target catchments have similar hydrological responses. Therefore, the study suggested further inspection methods to minimize the model uncertainty in the study catchment. This study enables researchers to exploit the river eco-regional classifications of South Africa to apply hydrologic models to estimate the components of water balance in arid/semi-arid catchments.
In a new paradigm shift related to integrated water resources management in the context of a river basin, attention is being drawn to consider the upstream and downstream impacts on the various water use entities. The river basin is increasingly acknowledged as the appropriate unit for analysis and management of water resources, especially as water availability becomes the primary constraint to agriculture. The irrigated agriculture in the Modder river basin, in the central South Africa, draws water from river pools and weirs. However, many small-scale farmers rely on rain-fed farming. A few years ago, the ISCW-ARC introduced a rainwater harvesting technique for these farmers, which is reported to have increased crop yield significantly compared to conventional practices. The research questions were: what is the potential expansion of this technique? and; what will be the implications of this practice on the downstream users if applied on a wider scale? A field survey showed that a fairly rapid spread of the application of the technique can be expected within the scope of home yard size, but no significant spread to community gardens and beyond is expected in the short term because of socio-economic constraints such as poverty, and lack of appropriate tools and basic farming skills.
Lucerne production is regarded as requiring high water inputs, making it necessary to understand its transpiration efficiency, especially in countries with water scarcity such as South Africa. The resurgent opportunities in the local lucerne markets prompted the publication of this short communication. The objective of this study was to quantify the transpiration efficiency of lucerne for different cutting periods during its first growing season. The study was conducted in a semi-arid area at Kenilworth Experimental Farm, University of the Free State, South Africa. Thirty field lysimeters of 1 800 mm diameter and 2 000 mm depth were arranged in two parallel rows and filled respectively with Clovelly and Bainsvlei soil types for the experiment. Surface drip irrigation was applied weekly and sub-irrigation applied daily to maintain a constant water table. The mean above-ground biomass production over 30-day cutting periods was 511 g m−2. A mean transpiration efficiency of 2.81 g m−2 mm−1 and a mean transpiration efficiency coefficient of 2.85 g kPa mm−1 were derived for the growing season. Both variables declined as the growing season progressed. Future work should ascertain the physiological and environmental factors that influence the declining trend in transpiration efficiency over the season.
A quasi-steady state method is presented for quantifying epidermal transpiration of epidermal strips where simple relations between transmembrane fluxes and parameters of diffusibility of penetrating compounds hold. Contrary to most permeability studies, we did not use astomatous, enzymatically isolated, or dried cuticular membranes, because these procedures are largely responsible for the problems cited in the literature. Instead, we used freshly harvested stomatous epidermal strips, thus avoiding the sorption of lipids by the cuticular membranes during enzymatic isolation. Our approach allowed estimation of amounts and composition of intracuticular soluble lipids. Diffusion coefficients (D-values) were calculated with smaller associated standard deviations and an order of magnitude lower than previously reported; the fresh material sorption of the diffusing compound by the membrane and hydration of the cuticular pores was greatly reduced. In the present study the hold-up time (te) ranged from 66.2 ± 0.3 to 110.3 ± 0.9sec. Furthermore, 0.1 μm thick membranes were used, contrary to previous studies of water permeability that used cuticles more than 2 μm thick. Because a small but constant flow of penetrant could be detected during the first half of the steady flow to te, small holes probably did not influence the reported permeability. Permeability coefficients (Pd) in the order of 0.65 × 10−9 ms−1 were calculated. Pd values in the order of 5.68 × 10−3 ms−1 were calculated when incomplete stomatal closure occurred, while when areas of mass flow were detected, Pd values in the order of 1.26 × 10−2 ms−1 were calculated. The degree of contamination of the epidermal strips by cellular debris was quantified and expressed as the total chlorphyll content per exposed surface area of the epidermal strip, and an average of 8.7% contamination was observed compared to the total leaf chlorophyll content. Leakage from the system was calculated to be approximately 0.18 × 10−10 ms−1, which represents an average 2.7% experimental variability. These results are discussed in terms of the limitations associated with using composite membranes that are stomatous and have trichomes, for possible application in drought tolerance selection.
In South Africa canola (Brassica napus L.) is cultivated in rotation with wheat under winter rainfall in the Western Cape Province. Expansion of the crop to the other eight provinces is advocated to reduce a shortage of locally produced plant oils. Moreover, canola can serve as a rotational crop for wheat in the summer rainfall provinces. In the central Free State, agronomic information for canola production is lacking. An experiment with a line source sprinkler irrigation system was conducted to establish the influence of water application levels (175, 233, 295, 351 and 420 mm) in combination with plant densities (25, 50, 75, 100 and 125 plants m−2) on yield responses, yield components and growth parameters of canola. Seed (653–4653 kg ha−1) and stover (1983–6733 kg ha−1) yields induced by the treatment combinations proved that canola has a high level of plasticity. Over the full range of water application levels, highest seed and biomass yields were realised at densities of 25 and 75 plants m−2, respectively. The compensation of yields at lower plant densities was due to the production of more branches, pods and seeds per plant. Under full irrigation, densities of 25 and 75 plants m−2 are optimal for seed and biomass production, respectively.
The saturated hydraulic conductivity (K sat ) is a key parameter for analyzing or modelling water flow and chemical transport in subsurface soil.Several methods were developed over the last thirty years to measure K sat which considered unsaturated and/or saturated flow of water around the holes where measurements are made.Most methods make use of devices to measure the infiltration rate into the soil and in combination with numerical models predict the K sat parameter.If maximum infiltration rate exceeds the infiltration capacity, runoff will be the consequence.Therefore maintaining a constant head means the rate of water supplied corresponds to the infiltration capacity.Commonly used devices for infiltration capacity measurements are infiltrometers, disc permeameters, sprinkler infiltrometers and different types of constant head permeameters.This paper evaluates the theory and practical application of the Aardvark constant head soil permeameter (ACHSP) in combination with the Glover equation for field measurement of K sat above the water table.The Glover equation has been criticized during the eighties because only the saturated flow around the hole was considered in its development.Several papers published since 2002, however, demonstrated that the Glover equation results are relatively close to the results obtained by other models for most practical applications and therefore the use of the Glover equation is justified.
Diurnal courses in gas exchange, photochemical efficiency and water relations were monitored during two late summers in three groups of adult Quercus robur L. trees, planted along an urbanization gradient that correlated positively with the degree of die-back exhibited by the trees. Leaf carbon:nitrogen ratios, proline and polyphenol levels were monitored to explain why the intermediate group of trees were more severely infested (p ≤ 0.01) with Asterolecanium quercicola (Bouché). All three groups of trees showed a significant correlation of net photosynthesis with photon flux density (PPFD), but A correlated more positively with the pre-dawn leaf water potential ψpd of the moderately (trees of group b, i.e. at the edge of town) and severely (trees of group c, i.e. urban) water-stressed trees. A of the rural trees and stomatal conductance (g) of the three groups of trees showed little correlation ψpd values. Possibly due to the long-term effect of stress, g, as reflected by changes in the transpiration rate (E), showed a significantly (p ≤ 0.01) higher sensitivity to relative ambient humidity (RH) in the trees of groups b and c. Photochemically, a close coupling was found to exist between A, ψpd, RH, the time needed to reach the maximum fluorescence level, i.e. FTm, and S, i.e. the complementary area normalized to the variable fluorescence, indicating that the trees were also affected at this level of organization. Proline accumulation occurred in the trees of group c but not in the trees of group b, as opposed to the polyphenolic concentrations which were significantly (p ≤ 0.05) higher in the trees of group b than in the trees of group c. A possible explanation for the higher infestation of A. quercicola on the trees in group b is given in terms of their host specificity and changes in these trees' nitrogen levels.
Abstract Rehabilitation of mine tailings dams is often a challenge due to a lack of nutrients and a poor humus reservoir prevailing in tailings soils. This is especially true for establishing longer lived species such as trees. For these reasons the effects of different soil ameliorants (woodchips compost, vermicompost, mature sewage sludge), added to the root system of Karee (Searcia lancea) saplings were tested in pot trials. Those pots were filled with platinum and gold tailings substrate as well as red clay soil, respectively. For three months plants remained in a greenhouse and were subsequently moved to a test field outside. Throughout the test period regular chl a fluorescence measurements were taken and subjected to JIP-test quantifying changes in photosynthetic vitality status. Additionally, growth measurements and one-off leaf analysis were carried out. Test plants growing on mine tailings experienced an up to 35% higher average photosynthetic vitality (PIABS) and improved nutrient supply, when treated with mature sewage sludge. Consequently, sewage sludge treated plants showed a higher biomass build-up rate and an up to 55% higher diameter growth, compared to control. In summary the experiments present a low cost alternative for reforestation enterprises on platinum and gold tailings dams in South Africa. KEY WORDS:: rehabilitationsoil improvementnutrient supplyplant vitality statusSouth Africa ACKNOWLEDGMENTS This work was funded by the National Research Foundation, South Africa and Impala Platinum Holdings Limited (Implats). We would also like to thank Jaco Bezuidenhout (NWU) for multivariate analyses and Mr. Derek Dean (ARC Potchefstroom) for providing technical assistance.
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