Leaf area changes and transpiration in vineyards under salt stress

De Clercq, Willem P. (1999-12)

Thesis (M.Sc. Agric.) -- University of Stellenbosch, 1999.

Thesis

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.

AFRIKAANSE OPSOMMING: Besproeiing van wingerd met brakwater is reeds 'n wesenlike probleem in die WesKaap Provinsie. Navorsing was deur die Waternavorsingskomrnissie geloods waar wingerd met ses grade van brakwater besproei was om brakwater se invloed op plantprestasie te meet. Die proef was tweeledig van aard met 'n perseel buite Robertson op die NIWW -proefplaas en 'n tweede op die Nietvoorbij proefplaas buite Stellenbosch. Daar was 6 brakwater behandelings nl., -40, 75, 150, 250, 350, 500 mSm-1 met 4 herhalings van elk. Die waterkwaliteit was beheer vanaf In inspuitstelsel gekoppel aan In hoe konsentrasie voorraad oplossing. Die voorraad oplossing het bestaan uit NaCl en CaCl2 gemeng in 'n Na:Ca verhouding. Beskrywing van die blaredak en blaredakstruktuur van 'n gewas is essensieel t.o.v. formulering en beskrywing van plantreaksie a.g. v. plant-omgewing interaksies. Daar was met hierdie studie gekyk na metingstegnieke om die blaredak deur niedestruktiewe metodes te beskryf en dus plantreaksie op verskillende brakwaterbehandelings te kwantifiseer. Metingstegnieke het bestaan uit fisiese destruktiewe metings en ligonderskeppings tegnieke waaronder die Sunfleck Ceptometer en Dcor C2000 Plant Canopy Analizer tel. Destruktiewe metings was slegs gedoen ter kalibrering van die nie-destruktiewe metodes. Die Dynamax Heat Balance Sapflow Meter was gebruik vir sapvloeimetings, om die verskille in transpirasie tussen behandelings waar te neem. Die gemete transpirasie was vergelyk met weerstasie afgeleide evapotranspirasie en ook met die natrium absorpsie verhouding van die verskillende gronde. Daar was gevind dat blaar oppervlakindekse wel duidelik behandelingsverskille uitwys. Daar is ook gevind dat teen die tyd dat verskille sigbaar is, daar reeds onomkeerbare skade aan die blare is. Blaar oppervlakindekse het dus wei gehelp om die behandelingsverskille uit te wys maar dit kan nie gebruik word in 'n produksie omgewing om blaarskade te help voorkom deur dit as 'n bestuurshulpmiddel aan te wend nie. Daarvoor was sapvloei metings gedoen om aan te toon dat verskille in sapvloei reeds bestaan voor blaarskade sigbaar is. Sapvloei metings sou dus met groter sukses aangewend kan word as 'n bestuurshulpmiddel en ook as navorsingshulpmiddel. 'n Goeie kalibreringsoefening om blaaroppervlak indekse akkuraat te bepaal m.b.v niedestruktiewe metodes, het gehelp om transpirasie en evapotranspirasie baie akkuraat te benader.

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