Die gebruik van operdwalle om 'n marginale, hidromorfe grond se fisiese toestand vir wingerdbou te verbeter

Myburgh, Philip (1989-12)

Thesis (MScAgric)--Stellenbosch University, 1989.

Thesis

ENGLISH ABSTRACT: Viticulture is increasingly extended to marginal soils including low-lying waterlogged soils. These soils demand Special soil management practises such as ridging. Ridging entails the heaping of the top soil in continuous bands to create favourable rooting conditions above restrictions in the deeper soil layers. This practise has been used with varying degrees of success, mainly because farmers used their own and sometimes wrong techniques. This research was undertaken to determine which method of ridge construction and ridge dimensions would offer optimal conditions for vine root growth. Results show that the active growing season can be devided in two periods if the soil is waterlogged during early spring. Ridging induces favourable soil physical conditions during the wet and waterlogged first part of the season. Due to the increase in depth to the water table, dryer, warmer and better aerated soil conditions prevail during this period. These favourable growth conditions reflect clearly in the shoot growth tempo and leaf water potential. Low soil water content and high soil temperatures in the ridged soil had a negative on vine growth during the second part of the season. However, according to the total shoot growth the effect of the initial favourable soil physical conditions dominated these negative effects. Although the unridged soil contained more available soil water during· the later stages of the growing season, it could not compensate for the poor growth during the beginning of the season. The deterimental effects due to low soil water content and high soil temperatures in ridges can be overcome with additional practices such as irrigation and mulching. The soil physical properties did not differ with respect to ridges of different height and width and therefore no differences in vine reaction could be measured. The increase in depth to the water table improved soil physical conditions to the same extent in all the ridged treatments. However, due to practical considerations, the double row ridges are recommended. Firstly, a wide trough is obtained to allow free tractor traffic without damaging the ridges. Secondly, 3700 vines can be planted per hectare if the distance between two adjacent ridges amounts to 4,5 m, i.e. a plant spacing of 1,2 m x 1,2 m x 4,5. This is significantly more than 2700 when a conventional narrow spacing of 1,2 m x 3,0 m is used with single row ridges. Thirdly, if microjets are used, only one irrigation line is needed for every two vine rows which implicates a financial advantage. During construction of ridges tractor traffic should be avoided on the loose soil to prevent compaction. Unstable soil should not be used for ridge construction since it may lead to run-off of rain and irrigation water. Additional soil preparation in the form of ripping to a depth of 600 mm is sufficient if the soil is to be ridged. Ripping enchances drainage if it is done in the correct slope direction. The loosened soil does not dry out to the same extent as the overlying ridged soil. Vine roots in the additional loosened soil will buffer the vineyard against dessication. Ridging impairs normal viticultural practises and it is therefor only recommended where conventional deep soil preparation and drainage cannot be done with permanent success.

AFRIKAANSE OPSOMMING: Wingerdverbouing word toenemend na marginale gronde (byvoorbeeld laagliggende versuipte gronde) uitgebrei. Sodanige gronde vereis spesiale grondbestuurspraktyke, soos byvoorbeeld operd. Operd behels die bymekaarwerk van die bogrond in die vorm van 'n aaneenlopende wal, om 'n gunstiger wortelruimte bokant beperkings in die ondergrond te skep. Wisselende welslae, is tot dusver met hierdie tegniek op wingerd behaal, omdat boere elkeen op hul eie, en dikwels verkeerde wyse, opgeerd het. Hierdie navorsing is onderneem om vas te stel watter metodes van walkonstruksie en -afmetings optimale toestande vir wortelgroei bied. Resultate toon dat die aktiewe wingerdgroeiseisoen op versuipte gronde in twee periodes verdeel kan word. Opgeerdte grond bied gunstige grondfisiese toestande gedurende die nat en versuipte eerste helfte van die seisoen; Vanwee die groter diepte na die watertafel word droer, warmer en beter deurlugte grondtoestande gedurende hierdie periode geskep. Hierdie gunstige I I groeitoestande het duidelik in die lootgroeitempo en blaarwaterpotensiaal gereflekteer. Gedurende die droer tweede periode vanaf middel November, het lae grondwaterinhoud en hoe grondtemperature in die operdwalle wingerdgroei benadeel. Die aanvanklike gunstige grondfisiese toestande wat opgeerdte grond induseer, oorskadu egter die latere nadelige effekte soos wat- geblyk het uit die beter lootgroei. Alhoewel die onopgeerdte grond gedurende die tweede deel van die seisoen oor meer grondwater beskik het, was dit nie voldoende om vir die swak groei aan die begin van die seisoen te kompenseer nie. Die nadelige effekte van operd soos lae grondwaterinhoud en hoe grondtemperature, kan egter tot 'n groot mate deur aanvullende praktyke soos besproeiing en deklaagbewerking die hoof gebied word. Sover dit verskillende walhoogtes en -vorm betref, kon geen grondfisiese verskille tussen hoe en lae, asook bree en smal walle - en dus ook in wingerdreaksie - gemeet word nie. Alle operdbehandelings om beide die diepte na die watertafel te vergroot en 'n oppervlakdreineringsfunksie te bewerkstellig, was dus suksesvol. Dubbelry-operd word egter vanwee praktiese oorwegings bo die enkelr-operd aanbeveel. Eerstens word 'n bree trog waarin trekker- en implementverkeer vrylik kan plaasvind verkry, sonder om die walle te beskadig. Tweedens kan daar 3 700 stokke per hektaar geplant word indien die afstand tussen die middelpunte van twee naasliggende walle 4,5 m beloop (dit wil se 'n plantwydte van 1,2 m x 1,2 m x 4,5 m). Hierteenoor kan in 'n relatief nou konvensionele enkelry met 'n plantwydte van 1,2 m x 3,0 m maar sowat 2 700 stokke per hektaar geplant word. Derdens is slegs een lyn mikrospuite vir elke twee wingerdrye nodig, wat finansieel groter voordele inhou. Tydens die konstruksie van operdwalle moet trekkerverkeer op die los grond vermy word om grondverdigting te voorkom. Onstabiele ondergrond moenie tydens die operdproses op die wal beland nie, want dit lei tot die afloop van _reen- en besgroeiingswater. Addisionele grondvoorbereiding in die vorm van vooraf skeurbewerking tot op 'n diepte van hoogstens 600 mm, is voldoende wanneer wingerdgrond opgeerd word. Die skeuraksie bevorder dreinering mits dit in die gewenste rigting uitgevoer word. Die losgeskeurde sone droog nie so vinnig uit soos die oorliggende opgeerdte grond nie. Wingerdwortels in hierdie sone verseker dat die wingerd beter teen uitdrogte gebuffer is. Aangesien operd wingerdboukundige praktyke belemmer, word dit slegs as laaste uitweg aanbeveel waar konvensionele diep grondvoorbereiding en dreinering nie met 'n redelike mate van permanensie uitgevoer kan word nie.

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