A study of within-vineyard variability with conventional and remote sensing technology

Strever, Albert E. (2003-12)

Thesis (MScAgric)--Stellenbosch University, 2003.

Thesis

ENGLISH ABSTRACT: In the past it was very difficult to visualise the extent and distribution of variability in growth vigour within vineyards. The advancement of remote sensing technology has changed this however, establishing new methods to assess and manage variability. Even though the causes and effects of within-vineyard variability in growth vigour are complex, new technologies offer better ways of monitoring, researching and managing these factors. In addition to the possible benefits of aerial or satellite remote sensing, new methods of mapping soil spatial variability as well as advances in georeferencing technologies supply precision tools to both researchers and producers. The scientific advancement of the technology, however, is currently the most important aspect needed. This is crucial to answer and explore fundamental questions regarding the use of the technology and the interpretation of results within the framework of the plant's observed reaction. Only then can the possible applications in vineyard management be optimised to address the management problems of extensive within-vineyard variation in growth vigour. The choice will always be to use the technology to manage the observed variability in order to limit the negative impacts of a heterogeneous harvest, or to identify the variability and its causes for the implementation of management practices aimed at a more homogenous vineyard and harvest. Whatever the case, extensive research is needed to provide tight correlations between information gathered with new technologies to assess variability and plant status, such as multi- and hyperspectral analysis, and ground-truthed results in the vineyard. Only then will it become evident which methods and analyses would be useful in the drive towards in-depth analysis and management of vineyards within the concept of precision viticulture and its derived advantages. With this in mind, the aim of this study was to establish an experimental model to use remote sensing technologies to identify and classify within vineyard variability with a subsequent analysis of the causes of variability and the effects on the plants. The targeted experimental model was a vineyard with highly heterogeneous above-ground growth. An aerial photograph of the vineyard was studied and manipulated to yield image pixel values used to quantify the degree of variability for different plots, which were chosen according to different plot layouts. Soil conditions were assessed on both a global and plot level, with extremely high pH and low resistance values in the soil in combination with erratic soil preparation practices found to be the main cause of variability. Soil physicochemical condition was also assessed during a soil profile pit study. Significant differences were found between several soil-related parameters measured for the higher and lower vigour levels and a strong correlation was also found between the resistance of a saturated soil paste and the image pixel values. Vegetative measurements also yielded highly significant differences between the vigour levels and confirmed the suitability of the vineyard to study within-vineyard variability. Some of these measurements were also strongly correlated with soil conditions as well as image pixel values. Trunk circumference proved to be an excellent measure for the level of variability, being linked strongly to canopy characteristics, soil conditions as well as the image pixel values. Leaf water potential measurements also yielded significant differences between the vigour levels. Harvest data and wine analyses showed the effect that vigour differences can have on grape composition and wine quality, even though the differences found here were much less than expected. Even though no clear preference was shown between the wines made from the different vigour levels, the lower vigour wine was considered fruitier. The overall quality of both experimental wines was however very high, considering that experimental winemaking techniques has been used. Hyperspectral measurements also confirmed differences between the vigour levels through a narrow-band NOVI (normalised difference vegetation index). It was also possible to show differences in certain biochemical compounds between the vigour levels on both a leaf and canopy level. Wavelength regions corresponding to carotenoid, chlorophyll a and chlorophyll b showed different spectral reactions in the leaves of more stressed (lower vigour) canopies, indicating possibilities for further studies. This study and its results is the first of its kind in the South African wine industry and paves the way for more focussed and in-depth analyses of the use of specifically multiand hyperspectral data to accurately assess within-vineyard vigour variability and the management thereof to yield optimum quality grapes for a specific wine target. Moreover, the approach adopted in this study is also echoed in other international research programs in prominent wine countries. The availability of scientific research regarding the optimal use and limitations of these technologies has the potential to revolutionise production management practices in the next few years in the viticultural industry.

AFRIKAANSE OPSOMMING: In die verlede was dit baie moeilik om die omvang en verspreiding van groeikragvariasie binne 'n wingerd te visualiseer. Die vordering gemaak op die gebied van afstandswaarneming-tegnologie het egter nuwe metodes beskikbaar gestel waardeur hierdie variasie in wingerde gemonitor en bestuur kan word. Selfs al is die oorsake en invloede van binne-wingerd-groeikragvariasie kompleks, verskaf nuwe tegnologieë verbeterde metodes om hierdie variasie te monitor, te bestuur en na te vors. Saam met die moontlike voordele wat lugfoto's en satelliet-afstandswaarneming teweegbring, verskaf nuwe metodes om ruimtelike variasie in grondfaktore te karteer, asook vordering in geoverwysingstegnologie, presisiehulpmiddels aan produsente én navorsers. Die wetenskaplike vordering van dié tegnologie is tans van groot belang. Die belang daarvan is om fundamentele vrae te ondersoek en te beantwoord rakende die gebruik van die tegnologie en die interpretasie van resultate binne die raamwerk van die waargeneemde reaksie in die plant. Dit sal die weg baan vir optimale toepassing van die tegnologie in wingerdbestuur om sodoende die bestuursprobleme wat deur binne-wingerdgroeikragvariasie teweeggebring word, aan te spreek. Die voorkeurkeuse is om dié tegnologie aan te wend om hierdie variasie te bestuur sodat die negatiewe impak van In heterogene oes teengewerk kan word, of om die variasie te identifiseer vir die implementering van bestuurspraktyke gemik op die skep van 'n meer homogene wingerd en oes. Dit is noodsaaklik dat uitgebreide navorsing gedoen word om noue verwantskappe vas te stel tussen inligting wat ingewin is met behulp van nuwe tegnologieë wat die variasie in plantstatus monitor, soos multi- en hiperspektrale analise, en inligting wat op grondvlak ingewin is. Hieruit sal dit duidelik wees watter metodes en analises die doeltreffendste is vir in-diepte analises en die bestuur van wingerde binne die konsep van presisie-wingerdkunde. Met inagneming van hierdie aspekte, was die doel van hierdie studie om 'n eksperimentele model daar te stel waardeur afstandswaarneming-tegnologie gebruik kan word om variasie binne wingerde te identifiseer en te klassifiseer deur analises van die oorsake van hierdie variasie en invloede op die plant. Die geteikende eksperimentele model was 'n wingerd met hoogs heterogene bogrondse groei. 'n Lugfoto van die wingerd is bestudeer en gemanipuleer om pixelwaardes te verskaf wat die graad van variasie vir verskillende eksperimentele plotte, wat aan die hand van verskillende plotuitlegte gekies is, te kwantifiseer. Grondtoestande is bestudeer op 'n globale én plotvlak, met uiters hoë pH en lae weerstande in kombinasie met verkeerde grondvoorbereidingspraktyke, wat geïdentifiseer is as die hoofoorsake vir die hoë vlakke van variasie. Grondfisiese en -chemiese toestand is ook tydens profielgatstudies bestudeer. Betekenisvolle verskille is gevind tussen verskeie grondverwante parameters gemeet vir plotte met onderskeidelik laer en hoër groeikrag, en 'n sterk verwantskap is gevind tussen grondweerstand en pixelwaardes, soos vanaf die lugfoto bepaal. Vegetatiewe metings het ook betekenisvolle verskille tussen die hoër en laer groeikragvlakke opgelewer, wat die geskiktheid van die wingerd vir die studie van binnewingerdvariasie in groeikrag bevestig het. Van hierdie metings was ook nou verwant aan grondtoestande, asook beeldpixelwaardes. Stamomtrek was 'n uitstekende maatstaf vir die vlakke van variasie, aangesien dit nou verwant was aan lowertoestande, grondtoestande, asook beeldpixelwaardes. Blaarwaterpotensiaal-metings het ook betekenisvolle verskille tussen die hoër en laer groeikragvlakke opgelewer. Oesdata en wynanalise het die uitwerking van groekragverskille op druifsamestelling en wynkwaliteit uitgewys, selfs al was die verskille wat gevind is minder as wat verwag is. Hoewel geen duidelike voorkeur tussen die wyne afkomstig van verskillende groeikragvlakke uitgewys kon word nie, was die wyn wat van die laer-groeikrag stokke gemaak was, meer vrugtig. Die algemene kwaliteit van beide wyne was egter baie hoog as in ag geneem word dat eksperimentele wynmaakprosedures gevolg is. Hiperspektrale metings het ook die verskille tussen groeikragvlakke bevestig deur 'n nou-bandwydte NDVI ("normalised difference vegetation index"). Dit was ook moontlik om verskille in sekere biochemiese komponente tussen die groeikragvlakke op 'n blaar- én lowervlak uit te wys. Golflengte-areas ooreenstemmend met karotenoïed, chlorofil a en chlorofil b het verskillende spektrale reaksies in die blare met hoër stresvlak (laer groeikrag) lowers ten toon gestel. Dit het moontlikhede vir verdere navorsing uitgewys. Hierdie studie en die resultate wat verkry is, is die eerste van sy soort in die Suid- Afrikaanse wynbedryf. Dit baan die weg vir meer gefokusde en in-diepte analise van die gebruik van spesifiek multispektrale en hiperspektrale data om binne-wingerdgroekragvariasie akkuraat te monitor en te bestuur met die oog op optimum wynkwaliteit vir 'n spesifieke produkdoelwit. Die aanslag van hierdie navorsing is ook sigbaar in ander prominente wynproduserende lande. Beskikbaarheid van wetenskaplike navorsing rakende die optimale gebruik en tekortkominge van hierdie tegnologieë het die potensiaal om produksiebestuurspraktyke in die wingerdbedryf in die komende jare te revolusionaliseer.

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