Faculty of Natural and Agricultural Sciences
School of Agricultural and Food Sciences
Department of Plant Production and Soil Science
Selected Highlights from Research Findings
Slags, or metal industry by-products, are regularly used as liming materials in agriculture due to their acid neutralising capacity. These materials often contain heavy metals as impurities – the type depending on the specific process and the dominant metals in the original ore. Several slag-users have voiced their concern about the metal levels in the slags used on the Eastern Highveld. From studies conducted on the slags it appears that the use of slags on the South African Highveld poses very little threat in terms of heavy metal pollution of the soil. At current application rates heavy metal additions to the soil are very small and the bulk of the metals added are in immobile fractions, therefore posing almost no risk in terms of leaching or plant-uptake.
Slakke, of metaalindustrie uitskotte, word gereeld gebruik as bekalkingsmateriale in landbou as gevolg van hul suur neutraliseringsvermoë. Hierdie materiale bevat gewoonlik swaarmetale as onsuiwerhede – die tipe hang af van die spesifieke proses asook die metale in die oorspronklike erts. Verskeie van die gebruikers van die slakke het genoem dat hulle bekommerd is oor die vlakke van die metale in die slakke. Uit studies wat op die Oostelike Hoëveld gedoen is, blyk dit dat die gebruik van slakke in hierdie gebied geen risiko van swaarmetaalbesoedeling van die grond inhou nie. Teen huidige toedieningstempos is swaarmetaaltoedienings aan die grond baie klein en is die meerderheid van die metale teenwoordig in immobiele fraksies. Dit hou dus so te sê geen risiko in in terme van plantopname of loging nie.
Contact person: Mr JH van der Waals.
The disposal of sewage sludge leads to the build-up of several heavy metals as well as organic material in acidified soils. Most of the metals are present in largely immobile fractions. Present guidelines stipulate that agricultural soils that receive sewage sludge should have pH values in excess of 6,5. In investigating the rehabilitation potential of such sacrificial lands it was found that these soils have very large pH buffer capacities: in excess of 50 tons of lime is required per hectare to increase the pH of the soil from 4 to 6,5. Further investigations indicated that some of the metals, notably Cu, Cd, Mn and Pb, increased in extractability after liming. This aspect contradicts the widely accepted practice of using lime and increasing pH to immobilise metals under the specific conditions and is the subject of further research.
Die storting van rioolslyk lei tot die opbou van verskeie swaarmetale asook organiese materiaal en lei ook tot ernstige versuring van die grond. Die meeste van die metale is egter in hoogs immobiele fraksies teenwoordig. Huidige riglyne stipuleer dat die pH van landbougrond waarop rioolslyk toegedien word bokant 6,5 moet wees. Tydens ‘n ondersoek na die herwinningspotentiaal van die grond is bevind dat die grond oor ‘n hoë buffervermoë beskik. Om die pH van die grond van 4 na 6,5 te lig verg meer as 50 ton kalk per hektaar. Verdere ondersoek het aangedui dat sekere metale, in besonder Cu, Cd, Mn en Pb, se ekstraheerbaarheid toegeneem het na bekalking. Hierdie verskynsel is teenstrydig met die aanvaarde gebruik van bekalking en pH verhoging om metale te immobiliseer onder spesifieke omstandighede. Dit is die onderwerp van verdere ondersoek.
Contact person: Mr JH van der Waals.
The mechanistic chemical equilibrium and soil water balance (SWB) model has been further refined and is proving an invaluable tool in quantifying the environmental impact of irrigation with large volumes of saline mine effluent. Alternative treatment strategies are at present extremely expensive and therefore not economically viable. Irrigation, on the other hand, is a cost effective, highly profitable approach to addressing this problem that creates employment opportunities and adds value to scarce water resources.
The SWB model was originally developed as a decision support tool for irrigation management. The Water Research Commission has acknowledged the model's potential to make a significant impact on irrigation management and has funded a technology transfer project to promote its use country wide. Several short courses have been presented, and with the recent development of a user-friendly, site specific irrigation calendar, the model's usefulness has been extended to a much wider audience than was the case previously. This means that even resource poor farmers who do not have computers and access to data from automatic weather stations, can also benefit from the accurate estimates of crop water use made by the model.
Die meganistiese chemiese ekwilibrium en grondwaterbalans-model is verder verfyn en word nou met vrug gebruik om die omgewingsimpak van besproeiing met groot volumes besoedelde mynwater te kwantifiseer. Alternatiewe waterbehandelingsmetodes is baie duur, terwyl besproeiing hiermee winsgewend bedryf kan word, werksgeleenthede skep en waarde kan toevoeg tot die skaars water hulpbron.
Die model was oorspronklik ontwikkel as besluitnemingsondersteuningsinstrument in besproeiingsbestuur. Die Waternavorsingskommissie het dié model se potensiaal om ‘n betekenisvolle impak op besproeiingsbestuur te maak, erken en het die tegnologie-oordrag projek befonds om die gebruik van die model landswyd aan te moedig. Verskeie kort kursusse is aangebied, en met die ontwikkeling van ‘n gebruikersvriendelike, terrein spesifieke besproeiingskalender is dié model se bruikbaarheid uitgebrei na ‘n baie groter gehoor. Dit beteken dat selfs dié boere wat nie rekenaars of toegang tot data van outomatiese weerstasies het nie, ook voordeel kan trek uit die akkurate vooruitskattings van gewas watergebruik wat deur die model gemaak word.
Contact person: Prof JG Annandale.
A two-dimensional model has been developed to more accurately quantify the water balance of hedgerow fruit tree crops. This sophisticated model will provide irrigation scientists with the tools to optimise a number of parameters, like row spacing, row orientation and pruning practice in the design of better management practices for micro-irrigated tree crops, and substantial irrigation water savings can be made. It also quantifies the contribution to crop water use from irrigation and from rainfall, and thus emphasises to the user the importance of getting the maximum benefit from the rainfall that is available - an opportunity often missed.
‘n Twee-dimensionele model is ontwikkel om die waterbalans van vrugteboorde meer akuraat te skat. Hierdie gesofistikeerde model sal besproeiingswetenskaplikes in staat stel om 'n aantal parameters, soos die spasiëring en oriëntasie van rye en snoei-praktyke te optimeer in die ontwerp van beter bestuurspraktyke vir boorde onder mikro-besproeiing, wat 'n aansienlike besparing op besproeiingswater kan meebring. Dit kwantifiseer ook die bydrae tot gewaswater van reënval en van besproeiingswater, en bring die gebruiker onder die besef dat dit belangrik is om die voordeel van beskikbare reënwater maksimaal te benut - 'n geleentheid wat dikwels verspeel word.
Contact person: Prof JG Annandale.
Allelochemicals (phytotoxins) that are produced and released by the alien invader weed Parthenium hysterophorus L. (common name: parthenium or Demoina weed) are responsible for its aggressive displacement of desirable species. Although the allelochemicals involved are well documented, and their biological activity on specific test species fairly well quantified, less is known about their specific location in the plant. Various plant parts were analyzed to determine the concentration of the allelochemical, parthenin, in them. Leaves had the highest levels of parthenin. Leaf washings yielded up to 13,4 mg g-1, and homogenized leaf material had 14,5 mg g-1. Selective collection of capitate-sessile trichomes from the leaf surface allowed parthenin to be determined at 24,3 mg g-1 in them. This trichome type contained virtually 100% parthenin, and on a per unit basis they held 0,3 µg parthenin, making them the main source of parthenin. Extrapolation of parthenin amounts to field-scale production makes it plausible that the high production and release of parthenin to a large extent could explain the supreme ability of P. hysterophorus to displace other plant species.
Allelochemikalieë (fitotoksiene) wat deur die uitheemse indringerplant Parthenium hysterophorus L. (algemene naam: parthenium of "Demoina weed") geproduseer en vrygestel word, is verantwoordelik vir hierdie spesie se aggressiewe verdringing van ander plantsoorte. Alhoewel die betrokke allelochemikalieë reeds deeglik beskryf is, en hul biologiese effekte op ander spesies redelik wyd ondersoek is, is min bekend oor hul lokalisering in die plant. Verskillende plantdele is ontleed om die konsentrasie van die belangrikste allelochemikalie, parthenin, daarin te bepaal. Blare het die hoogste konsentrasie parthenin bevat. Loog vanaf blare het 13,4 mg g-1, en gehomogeniseerde blaarmateriaal 14,5 mg g-1, opgelewer. Selektiewe versameling van ‘n spesifieke trichoomtipe op die blaaroppervlak het die teenwoordigheid van feitlik 100% parthenin teen 24,3 mg g-1 daarin aangetoon. Op ‘n per eenheid basis het hierdie trichoomtipe 0,3 µg parthenin bevat. Ekstrapolering van hierdie produksiepotensiaal na die veldsituasie ondersteun die vermoede dat produksie van groot hoeveelhede parthenin, wat in ‘n bepaalde trichoomtipe op die blaaroppervlak van hierdie plant geproduseer en geberg word, die vermoë daarvan om ander soorte te verdring grootliks kan verklaar.
Contact person: Prof CF Reinhardt.
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