Response of Vitis vinifera L. cv. Merlot to Low Frequency Irrigation and Partial Root Zone Drying in the Western Cape Coastal Region – Part II. Vegetative Growth, Yield and Quality

The impact of five drip irrigation strategies on vegetative growth, yield and quality of Merlot/99R was comparedto a non-irrigated control (T1) in the coastal region of the Western Cape province. Irrigations at pea size,véraison and post-harvest, either applied in grapevine rows (T2) or work rows (T4), tended to increase berrymass and yield compared to T1. More frequent irrigation at pea size, midway between pea size and véraison,at véraison, midway between véraison and harvest, and post-harvest, applied either in the grapevine rows (T3)or work rows (T5), increased berry mass and yield. A partial root zone drying (PRD) strategy, obtained byswitching subsurface irrigation in the work rows between alternating rows at approximately 14-day intervals(T6), induced a similar trend. Under the given conditions, yield only increased when irrigation plus rainfallfrom bud break in September until harvest in February/March increased from ca. 200 mm to 400 mm. Morewater did not cause any further yield increases. Although low frequency irrigation increased yields comparedto T1, it did not affect sensorial wine quality characteristics negatively. Non-irrigated grapevines producedthe smallest berries, but did not necessarily produce wine superior in quality. The PRD strategy reduced winequality, particularly when irrigation was applied at a high frequency between switches. The latter strategy onlyimproved irrigation water productivity when compared to conventionally irrigated grapevines that receivedunnecessary high volumes of water. Subsurface irrigation applied in the work rows did not affect grapevineresponses compared to irrigation in the grapevine rows

Response of Vitis vinifera L. cv. Merlot to Low Frequency Drip Irrigation and Partial Root Zone Drying in the Western Cape Coastal Region – Part I. Soil and Plant Water Status

The impact of five drip irrigation strategies on water status in Merlot/99R was compared to a non-irrigatedcontrol (T1) in the coastal wine grape region of the Western Cape province, South Africa. Relationships betweenpredawn (ΨPD), leaf (ΨL), stem (ΨS) and total diurnal (ΨTot) water potential made it possible to classify grapevinewater status in terms of ΨL, ΨS, or ΨTot according to previous classifications derived from ΨPD. Around véraison,T1 grapevines already experienced moderate to strong water constraints (ΨS < -1.0 MPa), followed by strongto severe water constraints (ΨS < -1.4 MPa) prior to harvest. Irrigations at pea size, véraison and post-harvest,either applied in grapevine rows (T2) or work rows (T4), did not reduce water constraints compared to T1.However, irrigations at pea size, midway between pea size and véraison, at véraison, midway between véraisonand harvest, and post harvest, either applied in grapevine rows (T3) or work rows (T5), reduced grapevinewater constraints compared to T1. Irrigation in work rows did not affect grapevine water status comparedto irrigation in grapevine rows. A partial root zone drying (PRD) strategy, obtained by switching subsurfaceirrigation in work rows between alternating rows at approximately 14-day intervals (T6), also reduced waterconstraints compared to T1. The water status in PRD grapevines clearly responded to the low plant availablewater (PAW) depletion levels in the alternating work rows in which irrigations were applied. There was minimallateral flow of irrigation water from subsurface irrigation lines in the work rows towards the grapevine rows

Estimating Transpiration of Whole Grapevines under Field Conditions

yield, growth and quality. Diurnal whole-plant transpiration, to be used in combination with a soilevaporation model to estimate vineyard evapotranspiration, was quantified by measuring sap flow ingrapevines. Sap flow was measured in grapevine trunks by means of the heat pulse velocity technique.Diurnal sap flow ranged from almost zero to c. 5 L/d per grapevine under various atmospheric, viticulturaland soil conditions. Sap flow showed good linear correlation with leaf area per grapevine and referenceevapotranspiration (ETo). Grapevines with similar leaf area trained onto horizontally orientatedtrellis systems transpired more than those on vertical trellises under the same atmospheric conditions.Approximately 90% of the variation in daily transpiration could be explained by means of multiple linearregression, with leaf area and daily ETo as the independent variables. However, grapevines with horizontaland vertical canopies required slightly different models

Juice and Wine Quality Responses of Vitis vinifera L. cvs. Sauvignon blanc and Chenin blanc to Timing of Irrigation during Berry Ripening in the Coastal Region of South Africa

The effects of additional irrigation during berry ripening on juice and wine quality in Sauvignon blanc and Cheninblanc grapevines were investigated. In all treatments the grapevines were irrigated when berries reached pea sizein December. One treatment received no further irrigation until after harvest. All of the remaining treatmentsreceived a second irrigation at véraison. Except for a single treatment, which was not irrigated during ripening,these treatments received a third irrigation either 14, 21, 28 or 31 days after véraison. The six treatments wereapplied in a field trial carried out in the Stellenbosch district of the Coastal winegrowing region of South Africaover consecutive seasons, between 1990 and 1993. Irrigation during berry ripening decreased theN concentration in the juice of both cultivars, but increased the P and Ca concentrations in the juice, though onlyin Sauvignon blanc. In neither cultivar were the juice K and Mg concentrations affected by irrigation during theripening period. The irrigation treatments did not affect sugar concentration in Sauvignon blanc grapes. Incontrast, sugar concentrations in Chenin blanc grapes that were irrigated 28 days after véraison were lower thanin grapes that were irrigated at pea size. Irrigation applied 21 days and 28 days after véraison resulted in highertotal titratable acidity in the juice of both cultivars. Irrigation applied 31 days after véraison, i.e. three days beforeharvest, raised juice pH in Chenin blanc grapes relative to grapevines that received a single irrigation at pea size.Although not consistent over seasons, irrigation applied during the later stages of ripening had negative effects onfresh vegetative aroma (green pepper, herbaceous or green cut grass flavours) and fullness of Sauvignon blancwines. Similarly, irrigation during the middle stages of ripening reduced the fermentation character (guava flavour)and fullness of Chenin blanc wines, though not in all seasons. Overall, irrigation during berry ripening tended toreduce wine quality in both cultivars

Water Status,Vegetative Growth and Yield Responses of Vitis vinifera L. cvs. Sauvignon blanc and Chenin blanc to Timing of Irrigation during Berry Ripening in the Coastal Region of South Africa

The effects of additional irrigation during berry ripening on water relations, growth and yield in Sauvignon blanc and Chenin blanc grapevines were investigated. In all treatments the grapevines were irrigated when berries reached pea size in December. One treatment received no further irrigation until after harvest. All of the remaining treatments received a second irrigation at véraison. Except for a single treatment, which was not irrigated during ripening, these treatments received a third irrigation at either 14, 21, 28 or 31 days after véraison. The six treatments were applied in a field trial carried out in the Stellenbosch district of the coastal winegrowing region of South Africa over consecutive seasons, between 1990 and 1993.  Irrigation at pea size berries and at pea size berries plus véraison increased leaf water potential, but did not affect vegetative growth and yield in either cultivar.  Relative to a single application at pea size berries, irrigation at pea size, at véraison and during ripening increased berry size in both cultivars, though not consistently, over the three seasons. However, this result must be viewed in terms of the fact that qualitative assessments of root development and distribution have revealed that effective soil preparation contributes to well-developed root systems. Results confirmed that these root systems could sustain vegetative growth and yield where a single irrigation was applied at pea size berries compared with additionalirrigations applied at véraison and during ripening. Irrigation applied at, and after, véraison resulted in yield losses of both cultivars when rainfall favoured Botrytis cinerea infection

Comparing Irrigation Systems and Strategies for Table Grapes in the Weathered Granite-gneiss Soils of the Lower Orange River Region

Drip and micro-sprinkler irrigation systems were compared in a Thompson Seedless/Ramsey tablegrape vineyard in a weathered granite-gneiss soil in the Lower Orange River region. For each system,two different irrigation strategies were investigated. Drip irrigation frequencies of two days or longer,induced more water constraints in grapevines compared to micro-sprinkler irrigation applied at the samefrequencies in the 1996/97 and 1997/98 seasons. Higher water constraints imposed by drip irrigation hadnegative effects on vegetative growth, berry size and grape quality compared to micro-sprinkler irrigation.However, responses of drip irrigated grapevines were comparable to micro-sprinkler irrigated grapevineswhen drip irrigations were applied daily in the 1998/99 and 1999/2000 seasons. Daily, early morning dripirrigation increased evapotranspiration (ET) by 6% compared to drip during the warmest part of theday. Drip irrigation suppressed weed growth considerably compared to micro-sprinklers. Daily ET of thedrip irrigated grapevines was substantially lower compared to micro-sprinkler irrigated grapevines thatreceived either two or three irrigations per week. In the case of micro-sprinklers, the higher frequencyincreased ET by 8% compared to the lower irrigation frequency. Since micro-sprinkler irrigationinvariably produced higher yields than drip irrigation during the four seasons, it should be the preferredsystem for irrigation of table grapes under the given atmospheric and soil conditions. If water resourcesare limited, or if high water cost reduces table grape profitability, drip irrigation merits considerationas an alternative. However, daily drip irrigation will be required during the growing season to maintainacceptable yields and grape quality

Using Grapevine Water Status Measurements for Irrigation Scheduling of Table Grapes - A Review

Water is becoming an increasingly scarce resource, so agriculture competes with urban and industrial needs for water. The production of table grapes with high export potential is the objective of South African producers. Growth, production, ripening aspects and quality parameters of table grapes can potentially be manipulated by means of irrigation. Consequently, it is an important management practice to help ensure economically viable table grape production. The objective for optimum irrigation scheduling should be to combine soil and plant water status measurements to calibrate grapevine water potential against reliable soil water monitoring instruments. Considering previously reported literature, poorer vegetative growth was related to lower levels of leaf water potential (YL). Given that berry size is a crucial aspect for yield as well as quality, it was evident that low levels of water potential can restrict berry development, thereby reducing berry size. Bunch mass was lower where there were lower levels of YL, pre-dawn leaf water potential (YPD) and total diurnal water potential (YTot). Poorer yield was generally related to lower levels of YL experienced throughout the season. However, lower levels of YL in the post-veraison period did not affect grapevine yield. The juice TSS did not respond to levels of YL but juice total titratable acidity (TTA) was related to lower levels of YL. Grape colour was affected where wet soil conditions induced higher levels of YL as well as where dry soil conditions induced lower levels of YL

Use of Boundary Lines to Determine Effects of Some Salinity-associated Soil Variables on Grapevines in the Breede River Valley

The boundary line concept was used to assess grapevine responses to salinity-associated soil variables. Soil chemical status and grapevine responses were measured in 13 vineyards in the Breede River Valley during the 2001/2002 season. Chardonnay grafted onto 110R and 101-14 Mgt, as well as Ruby Cabernet on the same two rootstocks, was included. The selected vineyards were representative of the variation in salinity-associated soil variables, as well as of leaf and juice element contents previously reported for South African vineyards. Under the prevailing conditions, the four scion-rootstock combinations responded similarly to the salinity-associated variables. The results confirm that soil pH(KCl) should be at least 6.0 for grapevines. The salinity threshold for vineyards in the Breede River Valley should be between 0.7 dS/m and 1.5 dS/m to avoid growth and yield reductions. To reduce the risk of Na toxicity, the SAR should be below 3, and the soluble Na content in the soil should not exceed 5 mg/kg. If gypsum is used to reduce soil Na, it should be applied judiciously to avoid soil SO4 accumulation, thereby reducing the risk of K and Mg deficiencies. Under the prevailing conditions, B and Cl toxicity apparently contributed to reduced vegetative growth. Therefore, soil Cl and B should be kept as low as possible, but care should be taken that B is not reduced to deficient levels. The boundary line concept proved to be useful for determining the effect of a single salinity-associated soil variable on grapevine response

Effects of Soil Ameliorants Produced from Recycled Glass on the Establishment of Table Grapes

Sandy, gravelly or stony soils with low nutrient supply or plant available water are common in the tablegrape growing regions of South Africa. A field study was carried out to determine if an ameliorant recycledfrom waste glass could enhance the nutrient and water supply during the establishing phase of tablegrapes. Two grades of ameliorant, i.e. fine and coarse, were incorporated into the soil before the grapevineswere planted. No ameliorants were applied to the control. After planting, the grapevines were irrigatedby using 2.1 L/h drippers. To establish whether the ameliorants could compensate if less water is applied,the same treatments were applied under 1.2 L/h drippers. In general, the grapevines responded positivelyto the higher irrigation volumes, irrespective of ameliorant application. Where higher irrigation volumeswere applied, the ameliorants did not have any positive effect on soil chemical or grapevine nutrientstatus compared to the control. This showed that the ameliorants were chemically inert under the givenconditions. The ameliorants also did not improve grapevine water status, vegetative growth, yield or juicecharacteristics. Likewise, the ameliorants could not compensate for any measured aspect of grapevineperformance where less irrigation was applied. In general, the ameliorants did not meet the expectations.Considering the additional costs of the ameliorant application, and the lack of positive grapevine responses,this practice cannot be justified under the given, or comparable conditions

Comparison of Three Different Fertigation Strategies for Drip Irrigated Table Grapes - Part I. Soil Water Status, Root System Characteristics and Plant Water Status

Three fertigation strategies were compared in a drip irrigated Dan-ben-Hannah/Ramsey vineyard nearPaarl in the Berg River Valley region of South Africa during the 2002/03 and 2003/04 seasons. Fertiliserswere applied either (i) three times per season, (ii) once a week from bud break to flowering, from fruit setto véraison and for six weeks after harvest or (iii) in five to seven pulses per day. For each of the fertigationstrategies, grapevines bore normal or high crop loads, viz. 26 or 36 bunches per grapevine respectively.Daily irrigation pulses of 20 to 40 minutes each maintained soil water matric potential above -0.01 MPa inthe wetted bulbs. Daily pulses accumulated to a seasonal total of ca. 490 mm irrigation compared to ca. 260mm for weekly irrigation. Root structures of grapevines irrigated by means of daily pulses had adapted byforming extremely dense root systems in the small wetted bulbs compared to the less frequently irrigatedgrapevines. Monitoring diurnal grapevine water status revealed that the different fertigation strategiesdid not affect water constraints up to véraison. During berry ripening, daily pulse irrigated grapevinesexperienced less water constraints in the morning, late afternoon and during the night than less frequentlyirrigated ones. However, the grapevines did not experience any detrimental water constraints throughoutthe season, irrespective of fertigation and irrigation frequencies or crop load. It was evident that grapevinewater status not only depends on the size of the root structure, but also on the soil environment in whichthe roots function