Open hydroponic systems in table grape production : a case study

[摘要] ENGLISH ABSTRACT:An open air hydroponic production system (OHS) is based on classic hydroponicprinciples, with the difference that it lacks climatological control because the plants arenot produced in greenhouses and are cultivated in the outside environment. In thesesystems the plant is provided with all the essential nutrients through the irrigationsystem, which is scheduled according to accurate measurements of the available soilwater, in three to seven pulses a day. The rationale is that, by delivering nutrients eachday, the mixes can be representative of what the plant actually requires for that specificphenological stage.The aim of this study was to monitor the usefulness and impact of OHS on tablegrape production within the framework of a case study. For this purpose, it wasnecessary that all factors involved in the development and growth of the plant should bestudied and integrated in a multidisciplinary approach. Currently very limited informationexists on basic guidelines for the effective implementation of these systems for tablegrape production, particularly with regard to local conditions. As a start, and to establishsome guidelines and measurable parameters for the implementation of these systems,vegetative growth parameters were analysed within the framework of yield and fruitquality. The experiments were performed in a commercial vineyard in the Paarl regionand the cultivars used were Dan ben Hannah (DBH) and Waltham Cross (WC).Relevant soil and climatic conditions, irrigation scheduling, fertiliser application, as wellas cultivation practices, were taken into account. The soil maps provided information onthe soil types identified in the blocks prior to the establishment of the two cultivars. Theconventionally treated vines were irrigated and fertilised according to historical blockdata, and the OHS-treated vines according to programmes established by two differentconsultants.The experimental layout included a comparison of conventional cultivation methodsand vines that had been switched over from conventional methods to OHS in the middleof 2000. All measurements within the different treatments were done at specificmeasuring points laid out statistically. Ten phenological stages were chosen to monitorthe various aspects throughout the season for both cultivars treated conventionally andhydroponically. All relevant climatic parameters were collected for this specificproduction unit. The growth, fertility and quality indicators of these cultivars under thementioned cultivation practices are discussed and established through quantitativeanalysisOne of the aims, namely to show that established table grape vines could adaptfrom micro-irrigation to drip irrigation within two seasons in terms of root adaptation, wasproven in this study. Initially the soil types were identified as Cartref, ClovellyandGlenrosa for both cultivars. The WC block contained an Avalon and the DBH aWestleigh soil type as well. The soil pits in all four treatments revealed the soil type tobe a Tukulu form with differences in the clay content. Active roots developedunderneath the drip lines for the OHS-treated cultivars, while the roots were still evenlydistributed over the entire soil profile for the conventionally treated vines. Also, bothcultivars adapted to OHS in terms of yield and production within two seasons, especiallyWC, which produced a higher yield in the 2001/2002 season than in the previous fourseasons.DBH showed a strong vegetative reaction to OHS in terms of excessive vegetativegrowth, which had an indirect effect on fruit quality and bud fertility. A higher rate of budmite 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, incombination with the irrigation and fertiliser programmes. The irrigation and fertiliserprogrammes were changed from the 2000/2001 to the 2001/2002 season because ofthe change in consultants. As a result of this change, the OHS-treated vines were givenvery high nitrogen, phosphorus, potassium and micronutrient applications in the2001/2002 season. The penetration of light in the canopy of the OHS-treated DBH waslower 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, bothOHS-treated cultivars were not fully adapted to the new system, as their pruning masswas lower than in the conventionally treated cultivars. No significant differences weredetermined for the winter cane starch content of both cultivars under conventional andOHS 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 apoor skin cell structure and higher Botrytis infection during cold storage. The OHStreatedcultivars showed more compact bunches, with an overall smaller rachisstructure, 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 theelemental 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 cultivarstherefore ripened earlier than the conventional treatments.One of the advantages of the use of OHS in table grape production shown in thisstudy was the ability to manipulate the phenology of the grapevine to provide fullyripened grapes a few days earlier than the conventionally treated grapes. This kind ofadvantage could be used to manipulate the production of table grapes for a bettermarket window.Despite its limitations, this study concluded that the use of OHS for table grapeproduction might be a useful tool for future production management, but that accuratemanagement regarding irrigation and nutrient applications is a prerequisite. This willhave to be developed systematically through experimentation to fully unlock thepotential of the OHS management system for table grape production. This studyprovides a starting point for future research to elucidate these aspects and has clearlyshown that even established vineyards can be switched to OHS in a relatively shortperiod of time. It is envisaged that the advantages of this system, as long as the correctmanagement protocols are in place, could have a positive effect on the production ofhigh quality fruit for the international market.

[发布机构] Stellenbosch University