The effect of wind on the performance of the grapevine

Pienaar, Jacobus Wilhelm (2005-12)

Thesis (MScAgric)--University of Stellenbosch, 2005.

Thesis

ENGLISH ABSTRACT: Wind, as a component of the environment, contributes to the viticultural concept of terroir in the South Western Cape region of South Africa. Many other components also contribute to terroir (e.g. soil, altitude, direction of slope, etc.) and it is difficult to quantify the contribution of each. A good terroir promotes slow and complete ripening of the berries. A vineyard on such a terroir produces good quality crops over time and the effects of climatic extremes on the performance of the vine are limited by this terroir. Although grapevines in the South Western Cape are exposed to strong synoptic southerly and southeasterly winds during the growing season and sea breezes add to the effect of wind in coastal areas, little is known about the effect of wind on grapevine performance. This preliminary study was undertaken to obtain more information on the effect of wind on some morphological and reproductive characteristics of Merlot nair. The aim was to obtain preliminary data which can serve as a basis for future studies on the effect of wind on grapevine performance. Important differences .in wind speed were measured spatially in a selected vineyard and exposure to wind was observed to result in essential viticultural differences. The effect of wind on vegetative parameters, canopy density, yield, berry composition and wine quality was investigated. Wind caused leaves on primary shoots of exposed vines to be smaller, but increased lateral growth in their fruiting zones. Sheltered vines had longer shoots but no significant differences were measured concerning cane diameter and pruning mass. Although it was expected that sheltered vines would have denser canopies, similar canopy densities were measured for both treatments. Vines exposed to wind responded with decreased stomatal conductance. As a result, leaf temperature was affected, showing differences between sheltered and exposed vines. Sheltered vines had more bunches per vine but fewer berries per bunch. As a result, bunches of sheltered vines were smaller than those of exposed vines. No significant difference was observed concerning the yield under the two treatments. The effect of wind on stomatal conductance had an essential impact on berry composition, thus directly influencing the quality of wine. Grapes from exposed vines showed a higher colour index. Berries from sheltered vines had significantly lower pH values and potassium concentrations and the malic acid content was lower than in berries from exposed vines. Wine from sheltered vines had more vegetative undertones in comparison with the stronger fruity character of exposed vines. A better acid balance, together with superior complexity (fullness/mouth feel), contributed to the better overall quality identified during the evaluation of wine produced from sheltered vines.

AFRIKAANSE OPSOMMING: Wind as 'n omgewingsfaktor dra by tot die wingerdkundige konsep van terrair in die Suidwes-Kaap streek van Suid-Afrika. Baie ander komponente dra ook by tot terrair (bv. grond, hoogte bo seespieël, rigting van helling, ens.) en dit is moeilik om die bydrae van elk te kwantifiseer. 'n Goeie terrair bevorder stadige en volledige rypwording van die korrels. 'n Wingerd gevestig op so 'n terrair produseer jaarliks hoë kwaliteit oeste met goeie sapsamestellings en die terrair beperk die negatiewe invloed van uiterste klimaatsomstandighede op wingerdprestasie. Alhoewel wingerde in die Suidwes-Kaap gedurende die groeiseisoen aan sterk sinopties suidelike en suid-oostelike winde blootgestel is en seebriese 'n bykomstige effek in kusgebiede het, is daar beperkte kennis oor die effek wat wind op wingerdprestasie het. Hierdie voorlopige studie is onderneem om meer inligting oor die effek van wind op sommige morfologiese en reproduktiewe eienskappe van Merlot noir in te win. Die mikpunt was om verwysingsdata in te samel wat as 'n basis vir toekomstige studies oor die effek van wind op wingerdprestasie kan dien. Belangrike verskille in windspoed is gemeet in die geselekteerde wingerd en waarnemings het getoon dat blootstelling aan wind tot kenmerkende wingerdkundige verskille gelei het. Die effek van wind op vegetatiewe parameters, lowerdigtheid, oesgrootte, druifsamestelling en wynkwaliteit is ondersoek. Wind het kleiner blare op primêre lote van wind-blootgestelde stokke veroorsaak, maar het laterale groei in hul trossones verhoog. Wind-beskermde stokke het langer lote gehad maar geen noemenswaardige verskille is ten opsigte van lootdeursnee en snoeimassa gemeet nie. Die verwagting was dat beskermde stokke digter lower sal hê, maar soortgelyke lowerdigthede is vir beide beskermde en wind-blootgestelde stokke gemeet. Stokke blootgestel aan wind het met 'n verlaagde huidmondjiegeleiding gereageer. Gevolglik is blaartemperatuur beïnvloed, met verskille tussen beskermde en blootgestelde wingerde. Beskermde stokke het meer trosse per stok maar minder korrels per tros gehad. As gevolg hiervan was die trosse van beskermde stokke kleiner as die van blootgestelde wingerde. Geen noemenswaardige verskille in die oesgroottes is tussen die twee behandelings gemeet nie. Die effek van wind op huidmondjiegeleiding het 'n belangrike impak op druifsamestelling gehad en het daarom 'n direkte invloed op wynkwaliteit gehad. Druiwe van blootgestelde stokke het 'n hoër kleurindeks getoon. Die pH en kaliumkonsentrasie van druiwe van beskermde stokke was merkbaar laer en het minder appelsuur gehad as die van die blootgestelde stokke. Die wyn van beskermde stokke het meer vegetatiewe geure gehad in vergelyking met die sterker vrugtige karakter van blootgestelde stokke. 'n Beter suurbalans, tesame met goeie kompleksiteit (volheid/mondgevoel), het egter meegebring dat beskermde stokke 'n beter wyngehalte lewer.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/50486
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