Open hydroponic systems in table grape production : a case study

Thesis (MScAgric)--University of Stellenbosch, 2003.

ENGLISH ABSTRACT: An open air hydroponic production system (OHS) is based on classic hydroponic principles, with the difference that it lacks climatological control because the plants are not produced in greenhouses and are cultivated in the outside environment. In these systems the plant is provided with all the essential nutrients through the irrigation system, which is scheduled according to accurate measurements of the available soil water, in three to seven pulses a day. The rationale is that, by delivering nutrients each day, the mixes can be representative of what the plant actually requires for that specific phenological stage. The aim of this study was to monitor the usefulness and impact of OHS on table grape production within the framework of a case study. For this purpose, it was necessary that all factors involved in the development and growth of the plant should be studied and integrated in a multidisciplinary approach. Currently very limited information exists on basic guidelines for the effective implementation of these systems for table grape production, particularly with regard to local conditions. As a start, and to establish some guidelines and measurable parameters for the implementation of these systems, vegetative growth parameters were analysed within the framework of yield and fruit quality. The experiments were performed in a commercial vineyard in the Paarl region and the cultivars used were Dan ben Hannah (DBH) and Waltham Cross (WC). Relevant soil and climatic conditions, irrigation scheduling, fertiliser application, as well as cultivation practices, were taken into account. The soil maps provided information on the soil types identified in the blocks prior to the establishment of the two cultivars. The conventionally treated vines were irrigated and fertilised according to historical block data, and the OHS-treated vines according to programmes established by two different consultants. The experimental layout included a comparison of conventional cultivation methods and vines that had been switched over from conventional methods to OHS in the middle of 2000. All measurements within the different treatments were done at specific measuring points laid out statistically. Ten phenological stages were chosen to monitor the various aspects throughout the season for both cultivars treated conventionally and hydroponically. All relevant climatic parameters were collected for this specific production unit. The growth, fertility and quality indicators of these cultivars under the mentioned cultivation practices are discussed and established through quantitative analysis One of the aims, namely to show that established table grape vines could adapt from micro-irrigation to drip irrigation within two seasons in terms of root adaptation, was proven in this study. Initially the soil types were identified as Cartref, Clovellyand Glenrosa for both cultivars. The WC block contained an Avalon and the DBH a Westleigh soil type as well. The soil pits in all four treatments revealed the soil type to be a Tukulu form with differences in the clay content. Active roots developed underneath the drip lines for the OHS-treated cultivars, while the roots were still evenly distributed over the entire soil profile for the conventionally treated vines. Also, both cultivars adapted to OHS in terms of yield and production within two seasons, especially WC, which produced a higher yield in the 2001/2002 season than in the previous four seasons. DBH showed a strong vegetative reaction to OHS in terms of excessive vegetative growth, which had an indirect effect on fruit quality and bud fertility. A higher rate of bud mite infection in the OHS-treated vines also had a negative influence on bud fertility. The excessive vegetative growth was due to a rainy 2001/2002 growth season, in combination with the irrigation and fertiliser programmes. The irrigation and fertiliser programmes were changed from the 2000/2001 to the 2001/2002 season because of the change in consultants. As a result of this change, the OHS-treated vines were given very high nitrogen, phosphorus, potassium and micronutrient applications in the 2001/2002 season. The penetration of light in the canopy of the OHS-treated DBH was lower than in the conventionally treated DBH as a result of the above-mentioned factors, but the situation in Waltham Cross was the opposite. In the winter season of 2001, both OHS-treated cultivars were not fully adapted to the new system, as their pruning mass was lower than in the conventionally treated cultivars. No significant differences were determined for the winter cane starch content of both cultivars under conventional and OHS treatments. Effective fertiliser uptake proved to be suboptimal, especially in the case of calcium. Fruit analyses showed a lower calcium content in the OHS-treated fruit, which led to a poor skin cell structure and higher Botrytis infection during cold storage. The OHStreated cultivars showed more compact bunches, with an overall smaller rachis structure, which was another reason for the higher Botrytis infection during cold storage. However, the more compact rachis structure could not be explained on the basis of the elemental analyses. The OHS-treated DBH showed a more intense red berry colour, while the OHS-treated WC had a higher Fosscan Brix value. Both OHS-treated cultivars therefore ripened earlier than the conventional treatments. One of the advantages of the use of OHS in table grape production shown in this study was the ability to manipulate the phenology of the grapevine to provide fully ripened grapes a few days earlier than the conventionally treated grapes. This kind of advantage could be used to manipulate the production of table grapes for a better market window. Despite its limitations, this study concluded that the use of OHS for table grape production might be a useful tool for future production management, but that accurate management regarding irrigation and nutrient applications is a prerequisite. This will have to be developed systematically through experimentation to fully unlock the potential of the OHS management system for table grape production. This study provides a starting point for future research to elucidate these aspects and has clearly shown that even established vineyards can be switched to OHS in a relatively short period of time. It is envisaged that the advantages of this system, as long as the correct management protocols are in place, could have a positive effect on the production of high quality fruit for the international market.

AFRIKAANSE OPSOMMING: 'n Oop hidroponiese produksiestelsel (OHS) is gebaseer op klassieke hidroponiese beginsels, met die verskil dat OHS nie klimatologies beheer kan word nie. Die plante word nie in glashuise of tonnelsisteme verbou nie, maar wei onder buitelug toestande. Binne hierdie sisteme word die plante van alle noodsaaklike voedingstowwe deur die besproeiingstelsel voorsien. Hierdie voedingstowwe word in drie tot sewe pulse per dag volgens akkurate beskikbare grondwaterbepalings geskeduleer. Die rasionaal is dat, deur die daaglikse lewering van voedingstowwe, die mengsels verteenwoordigend is van die plant se behoefte vir 'n spesifieke fenologiese stadium. Die doel van die studie was om die bruikbaarheid en impak van OHS op tafeldruifproduksie binne die raamwerk van 'n gevallestudie te monitor. Alle faktore wat by die groei en ontwikkeling van die plant betrokke is, moet in 'n multidissiplinêre benadering bestudeer en geïntegreer word. Daar is tans slegs beperkte inligting oor die basiese riglyne en effektiewe implementering van dié sisteme vir tafeldruifproduksie wat spesifiek is vir plaaslike toestande. As 'n beginpunt, en om sekere riglyne en meetbare parameters vir die implementering van die sisteme te vestig, is vegetatiewe parameters binne die raamwerk van opbrengs en vrugkwaliteit geanaliseer. Alle eksperimente is in kommersiële wingerdblokke in die Paarl-omgewing uitgevoer. Die kultivars wat vir die studie gebruik is, is Dan ben Hannah (DBH) en Waltham Cross (WC). Alle relevante grond- en klimaatstoestande, sowel as besproeiingskedulering, bemestingprogramme en verbouingspraktyke is vir die projek in ag geneem. Ou grondkaarte het inligting ten opsigte van die verskillende grondtipes wat voor die vestiging van die verskillende kultivars geïdentifiseer is, verskaf. Die wingerde, onder konvensionele behandeling, is volgens historiese blokdata besproei en bemes, terwyl die wingerde onder OHS volgens geskeduleerde programme wat vanaf konsultante verkry is, besproei en bemes is. Die eksperimentele uitleg het 'n vergelyking van konvensionele verbouingsmetodes en wingerde wat in die middel van 2000 van konvensionele na OHS-verbouing oorgeskakel is, ingesluit. Alle metings en analises binne die verskillende behandelings het by spesifieke statistiesbepaalde punte plaasgevind. Tien fenologiese stadia is gekies om die verskillende aspekte vir beide kultivars onder konvensionele en OHSbehandeling gedurende die seisoen te monitor. Alle relevante klimaatsdata is vir die spesifieke produksie-eenheid aangevra. Alle groei-, vrugbaarheids- en kwaliteitsparameters van die kultivars onder die bogenoemde behandelingsmetodes is bespreek en gevolglik deur kwantitatiewe analises bepaal. Een van die doelwitte, naamlik om uit te vind of reeds gevestigde ouer wingerde in terme van wortelaanpassing binne twee seisoene kan aanpas van mikrobesproeiing na drup OHS, is deur die studie bevestig. Aanvanklik was die grondtipes geidentifiseer as die vorme, Cartref, Clovelly en Glenrosa vir beide kultivars, met 'n Avalon vorm adisioneel by WC, en 'n Westleigh vorm by die DBH. Grondprofiele het egter getoon dat die grondtipes vir al vier behandelings 'n Tukulu vorm is met verskillende klei inhoude. Aktiewe wortels het vir die OHS-behandelde wingerde onder die druppers ontwikkel, terwyl die wortels in die konvensionele behandeling steeds eweredig oor die hele grondprofiel versprei was. Beide kultivars het ook in terme van opbrengs en produksie binne twee seisoene ná die oorskakeling van die konvensionele behandeling na OHS aangepas. WC het in die 2001/2002 seisoen 'n hoër opbrengs gelewer as in die vorige vier seisoene. Afgesien van die goeie aanpasbaarheid, het DBH 'n sterk vegetatiewe groeireaksie ten opsigte van die OHS-behandeling getoon, wat 'n indirekte effek op vrugkwaliteit en oogvrugbaarheid geopenbaar het. 'n Hoër mate van knopmiet infeksie in die OHSbehandelde stokke kon ook 'n negatiewe bydrae tot oogvrugbaarheid gemaak het. Die sterk vegetatiewe groei kon aan die hoër reënval gedurende die 200112002 groeiseisoen, tesame met die besproeiings- en bemestingsprogramme, toegeskryf word. Die besproeiings- en bemestingsprogramme is verander van die 2000/2001 seisoen na die 2001/2002 seisoen weens die aanstelling van 'n ander konsultant. As gevolg van hierdie verandering het die OHS-behandelde stokke baie hoë toedienings van stikstof, fosfaat, kalium en mikroelemente in die 2001/2002 seisoen ontvang. Sonligpenetrasie in die wingerdlower van die OHS-behandelde DBH was laer as in die konvensionele behandeling as gevolg van die bogenoemde faktore. Die situasie vir WC was egter die teenoorgestelde. Tydens die winterseisoen van 2001 was beide oorgeskakelde kultivars nie ten volle by die nuwe OHS-behandeling aangepas nie, soos gesien kan word in die laer lootmassas in vergelyking met die konvensionele kultivars. Geen beduidende verskil is vir die hoeveelheid stysel in die winterlote van beide kultivars onder konvensionele en OHS-behandeling verkry nie. Effektiewe voedingstofopname was suboptimaal, veral betreffende kalsium. Vruganalises het 'n laer kalsiuminhoud in die OHS-behandelde druiwe getoon, wat aanleiding gegee het tot 'n swakker seistruktuur in die druiwedoppe en 'n hoor mate van Bottytis-infeksie gedurende koelopberging. Die OHS-behandelde kultivars het meer kompakte trosse getoon met kleiner trosraamwerke, wat ook aanleiding kon gegee het tot 'n hoër Botrytis-infeksie. Die kleiner trosraamwerke kon nie deur voedingstofanalises verklaar word nie. Die OHS-behandelde DBH het 'n hoër kleurintensiteit getoon, en die OHS-behandelde WC het 'n hoër suikerinhoud getoon ten opsigte van die konvensionele behandeling. Beide OHS-behandelde kultivars was dus vroeër ryp as die konvensionele behandelings. Een van die voordele van OHS wat uit die studie voortspruit, is die vermoë om wingerdfenologie te manipuleer om ryper druiwe vroeër in die seisoen te verkry. Hierdie tipe voordeel kan aangewend word om druiwe vir "n beter markvenster te produseer. Hierdie studie, tesame met al sy beperkinge, kom tot die gevolgtrekking dat die gebruik van OHS vir tafeldruifproduksie 'n nuttige instrument vir toekomstige produksiebestuur is, maar dat die optimale bestuur van besproeiing en bemesting as kritiese faktore beskou moet word. Hierdie faktore sal sistematies deur intensiewe navorsing ontwikkel moet word om die volle potensiaal van OHS te ontsluit, spesifiek vir tafeldruifproduksie. Hierdie studie kan as 'n beginpunt gebruik word vir toekomstige navorsing vir meer toegeligte verklarings van die bogenoemde aspekte, veral met die voordeel dat reeds gevestigde wingerde maklik en vinnig by OHS kan aanpas. Die voordele van OHS kan 'n groot positiewe invloed op die produksie van hoër kwaliteit tafeldruiwe vir die internasionale mark hê, mits die regte bestuursriglyne in plek is en toegepas word.