Browsing by Author "De Clercq, Willem P."

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    Applying the water-energy-food nexus to farm profitability in the Middle Breede catchment, South Africa
    (Academy of Science of South Africa, 2018) Seeliger, Leanne; De Clercq, Willem P.; Hoffman, Willem; Cullis, James D. S.; Horn, Annabel M.; De Witt, Marlene
    The water-energy-food nexus has emerged as a useful concept to understand the multiple interdependencies that exist between the water, energy and food sectors. The nexus is an ambitious attempt to work across disciplines and scales to understand the workings of these complex systems. It is, however, criticised for being more of a general framework than a practical methodology because of the vast amount of data it would need to make real-life contributions to sustainable development. We show how the nexus approach, when used within a farm budget model, can transform the problem focus in water governance. By changing the relationship among water, energy and food production of a farm, profitability is significantly changed. The water-energy-food nexus debate is discussed within the context of the South African water sector, particularly the Breede River Catchment. Working from within the farm budget model, we demonstrate the impact of moving from an irrigation canal system that requires electricity for pumping, to a gravity-fed piped irrigation system in the Middle Breede River. The finding is that the water-energy-food nexus has the potential to unlock groundbreaking solutions to complex problems in agricultural water management when used in appropriate modelling systems.
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    Leaf area changes and transpiration in vineyards under salt stress
    (Stellenbosch : Stellenbosch University, 1999-12) De Clercq, Willem P.; Smith, V.; Lambrechts, J. J. N.; Stellenbosch University. Faculty of AgriSciences. Dept. of Plant Pathology.
    ENGLISH SUMMARY: Irrigation of vines with saline water has long been a problem in the Western Cape region. Research in this respect financed by the Water Research Commission was done on vines to test the effect of 6 levels of irrigation water quality on production. The experiment consisted of two sites namely one at the Robertson experimental farm of the ARC outside of Robertson and the other on the Nietvoorbij experimental farm outside Stellenbosch. Each site had 6 treatments replicated 4 times. The treatments consisted of water with electrical conductivities of -40, 75, 150, 250, 350, 500 mS/m. The saline water was produced and controlled by a computerised injection system that injected a high concentration stock solution into the irrigation system. The stock solution consisted ofNaCI and CaCl2 mixed to a Na:Ca ratio. Description of the canopy surface and structure per plant is essential to the formulation and description of plant reaction resulting from plant-environmental interaction. This study looked at measurement techniques to non-destructively describe and quantify the reaction of canopies to different saline treatments. Measurement techniques consisted of physical destructive and non-destructive light interception techniques with special reference to the use of the Sunfleck Ceptometer and Dcor C2000 Plant Canopy Analyser. Destructive measurements were only done to calibrate the non-destructive techniques. The Dynamax Heat Balance Sap Flow Meter was used to measure differences in sap flow rate between plants from different treatments. The measured transpiration was compared with weather station derived evapotranspiration as well as the sodium absorption ratio of the different soils. It was found that leaf area indices do show treatment effects very clearly. It was also found that by the time treatment effects were visible, leaf damage was already irreversible. The method clearly highlights treatment effects but cannot be used in a production environment to help prevent leaf damage as a management tool. Sap flow measurement was done to show that sap flow is more sensitive and that differences do occur before leaf damage is visible. Sap flow measurements can therefore be used with greater success as a management and a research tool. A good calibration exercise to determine leaf area indices non-destructively led to the ability of producing reliable transpiration and evapotranspiration data.
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    Quantifying the catchment salt balance : an important component of salinity assessments
    (Academy of Science of South Africa, 2015) Bugan, Richard D. H.; Jovanovic, Nebo Z.; De Clercq, Willem P.
    Soil and stream salinisation is a major environmental problem because it reduces the productivity of landscapes and degrades water quality. The Berg River (South Africa) has been exhibiting a trend of increasing salinity levels, which has primarily been attributed to the manifestation of dryland salinity. Dryland salinity occurs as a result of changes in land use (indigenous vegetation to agriculture and/or pasture), which cause a change in the water and salt balance of the landscape, consequently mobilising stored salts. The quantification of salinity fluxes at the catchment scale is an initial step and integral part of developing dryland salinity mitigation measures. The objective of this study was to quantify the salinity fluxes in the Sandspruit catchment, a tributary catchment of the Berg River. This included the quantification of salt storage, salt input (rainfall) and salt output (in run‑off). The results of the catchment salt balance computations indicate that the Sandspruit catchment is exporting salts, i.e. salt output exceeds salt input, which may have serious implications for downstream water users. Interpolated regolith salt storage generally exhibited increasing storage with decreasing ground elevation. A salinity hotspot was identified in the lower reaches of the catchment. It is envisaged that the data presented in this study may be used to classify the land according to the levels of salinity present; inform land management decisions; and provide a guide and framework for the prioritisation of areas for intervention and the choice and implementation of salinity management options. The data which were generated may also be used to calibrate hydrosalinity models.
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    Trace element composition of two wild vegetables in response to soil-applied micronutrients
    (Academy of Science of South Africa, 2014) Mavengahama, Sydney; De Clercq, Willem P.; McLachlan, Milla
    Wild vegetables are an important commodity in the subsistence farming sector. They are considered to be rich in micronutrients and can therefore be used to overcome inadequate nutrition. However, research on micronutrients in wild vegetables remains limited and sporadic. In this study, we evaluated the responses of two wild vegetables – Corchorus olitorius and Amaranthus cruentus var. Arusha – to micronutrients added to the soil in comparison with a reference crop, Swiss chard (Beta vulgaris var. cicla). Swiss chard concentrated significantly (p<0.01) higher amounts of Cu, Zn and Mn in the leaves than did the wild vegetables. Variations in micronutrients among the vegetables were greater for Zn (72–363 mg/kg) and Mn (97.9–285.9 mg/kg) than for Cu (8.8–14 mg/kg). C. olitorius had the least capacity to concentrate Mn and Zn in the leaves. However, C. olitorius concentrated significantly more Fe (327 mg/kg) in the leaves than did A. cruentus (223 mg/kg) or B. vulgaris (295 mg/kg). The mean per cent S concentration in the leaves ranged from 0.26% in C. olitorius to 0.34% in A. cruentus and B. vulgaris. We conclude that the different vegetables had different abilities to concentrate Cu and Zn in the order B. vulgaris > A. cruentus > C. olitorius. These results seem to contradict the belief that wild vegetables have an inherent ability to concentrate mineral micronutrients in their tissues.