Water footprint analysis to improve water use efficiency in table grape (Vitis vinifera L. cv. Crimson seedless) production. A South African case study

Thesis (PhD)--Stellenbosch University, 2018.ENGLISH ABSTRACT: Water scarcity is a major impediment to agricultural production, warranting economically viable water use strategies globally. The aim of this study was to evaluate the effects of differing cultivation conditions as well as environmental effects on table grapes (Vitis vinifera L. cv. Crimson Seedless) in terms of plant growth, plant physiology, yield water use efficiency (WUEy) and irrigation water use efficiency (WUEirr) in the Hex River Valley of the Western Cape, South Africa. The experiment consisted of four commercial vineyard blocks with the following irrigation system/soil scenarios: (1) drip on sandy clay loam; (2) micro-sprinkler on sandy clay loam; (3) micro-sprinkler on loamy fine sand and (4) drip on sandy clay loam. No treatment was applied in this study, and standard viticulture management practices as recommended for the production of export quality Crimson Seedless table grapes were applied in each block by the specific farm. The blue water footprint along the production chain only was determined for three regions in South Africa (one winter & two summer rainfall areas). Data used for the water footprint analysis were obtained through interviews and questionnaires. FruitLook data were also validated against field measurements. The four selected blocks showed great variability in terms of their soil characteristics and vegetative growth responses. Block D had vigorous growth in both seasons and the highest yield during the 2013/14 season, with the best fruit quality in both seasons. In contrast, Block A had poor vegetative growth, lower yield, as well as poor fruit quality in both seasons. Blocks B and D had higher specific leaf area (SLA). Blocks A and B had a tendency towards thinner leaves, which could have been linked to the lower stem water potential (ΨS) measured in those blocks at the different phenological stages. Higher values of net carbon assimilation rate and stomatal conductance corresponded with larger berry size and higher yield. The two blocks that were irrigated with micro-sprinklers had higher irrigation volumes and evapotranspiration (ET). Furthermore, the two micro-sprinkler irrigated blocks had a tendency towards a higher WUEy in the 2014/15 season, due to the higher ET and yield measured in these blocks. The drip irrigated Block D had a higher WUEirr in both seasons, and also produced grapes of the best quality, which means a certain stress level can be applied even when grapevines are cultivated for table grape production, without forfeiting fruit quality. Thus, using a drip irrigation system and irrigation applications as applied for Block D and under similar conditions to that in this study, could reduce the volume of irrigation water used and contribute to saving water. The regional average blue water footprint (WF) over two seasons was 210.35 m3/ton, 392.19 m3/ton and 272.42 m3/ton for the Western Cape, Lower Orange River region and the Northern Province respectively. The regional average WUEy values for both seasons was 5.04 kg/m3, 3.00 kg/m3 and 3.68 kg/m3 for Western Cape, Lower Orange River and Northern Province regions, respectively. Water footprints provide useful information on the water use of a specific area and strategies to improve WUE can be developed based on this information. This information can aid in decision making as to which crop can be produced sustainably with better economic benefits to the production area. Thus, WF determination can be used as a tool to raise awareness, as well as determine crop efficiency, which can be used in debates and decision making regarding water allocations. FruitLook data validation also showed a potential to be used in irrigation management decisions that could contribute to improved WUE. grapevines in general and table grapes specifically, were desktop studies and did not include actual plant growth and physiological measurements. Additionally, most of the global data available do not make a distinction between the different grape types (table grapes, raisin & wine grapes). The plant based measurements in this study also contributes to the scientific knowledge and understanding of how the grapevine’s water use and performance is affected by different soil types and irrigation systems, through direct plant based measurements during critical phenological stages.AFRIKAANSE OPSOMMING: Waterskaarste is ‘n uiters belangrike beperking in landbouproduksie. Gevolglik is ekononies volhoubare watergebruikstrategië noodsaaklik. Die doel van hierdie studie was ‘n ondersoek na die effek van verskillende verbouingstoestande, asook omgewingseffekte op tafeldruiwe (Vitis vinifera L. cv. Crimson Seedless) in terme van plantgroei, fisiologie, produksie-watergebruik-effektiwiteit (WUEy) en besproeiingswatergebruik-effektiwiteit (WUEirr) in die Hexriviervallei van die Wes-Kaap, Suid-Afrika. Die eksperiment het bestaan uit vier kommersiële wingerdblokke met die volgende besproeiingstelsel-grond scenario’s: (1) drupbesproeiing op sand-klei-leem; (2) mikrospuit op sand-klei-leem; (3) mikrospuite op leem-fynsand; en (4) drupbesproeiing op sand-klei-leem. Geen behandeling is toegepas in hierdie studie nie en standaard wingerdkundige bestuurspraktyke soos aanbeveel vir die produksie van uitvoergehalte Crimson Seedless tafeldruiwe is toegepas in elke blok op die spesifieke plaas. Die blou watervoetspoor van die produksiesproses alleen is bepaal vir drie streke in Suid-Afrika (een winter- en twee somerreënvalgebiede). Data gebruik vir die watervoetspoorontledinig is verkry deur middel van onderhoude en vraelyste. FruitLook data is ook geverifieer teen veldmetings. Die vier geselekteerde blokke het groot variasie getoon in terme van grondeienskapppe en vegetatiewe groeireaksies. Blok D het die sterkste groeikrag in beide seisoen gehad, die hoogste produksie in die 2013/14 seisoen, asook die beste druifgehalte in beide seisoene. In teenstelling hiermee, het Blok A swak vegetatiewe groei, swak produksie, asook swak druifgehalte in beide seisoene gehad. By blokke B en D is ‘n hoër spesifieke blaaroppervlak (SBO) gevind. Vir Blokke A en B is ‘n tendens van die voorkoms van dunner blare gevind, wat geassosieer kan word met die laer blaarsteelwaterpotensiaalwaardes (ΨS) gemeet in daardie blokke gedurende die verskillende fenologiese stadia. Hoër netto-waardes vir koolhidraat-assimmilasietempo’s en huidmondjiegeleiding was geassosieer met groter korrels en hoër produksie. Die twee blokke wat met mikrospuite besproei was, se besproeiingsvolumes en evapotranspirasie (ET) was hoër. By die twee mikrospuit besproeide blokke is ‘n tendens van hoër WUEy in die 2014/15 seisoen gevind, weens die hoër ET en opbrengs gemeet in hierdie bloke. Die drupbesproeide Blok D het ‘n hoër WUEirr in beide seisoene gehad en het ook die beste gehalte druiwe gelewer in beide seisoene, wat aandui dan selfs in tafeldruifverbouing ‘n sekere mate van vogspanning toegepas kan word sonder dat vruggehalte benadeel word. Dus, gebruik van ‘n drupbesproeiingstelsel en besproeiingstoedienings soos toegepas vir Blok D, onder soortgelyke toestande as in hierdie studie, kan die volume besproeiingswater gebruik verminder en bydra tot waterbesparing. Die streeksgemiddelde blou watervoetspoor (WV) oor die twee seisoene was onderskeidelik 210.35 m3/ton, 392.19 m3/ton en 272.42 m3/ton vir die Wes-Kaap, Benede-Oranjeriviergebied en die Noordelike Provinsie. Die streeksgemiddelde WUEy-waardes oor beide seisoene was onderskeidelik 5.04 kg/m3, 3.00 kg/m3 en 3.68 kg/m3 vir die Wes-Kaap, Benede-Oranjeriviergebied en die Noordelike Provinsie Watervoetspoorwaardes verskaf waardevolle inligting oor watergebruik in ‘n spesifieke gebied en strategieë om WUE te verbeter kan ontwikkel word op grond daarvan. Hierdie inligting kan bydra tot besluitneming ten opsigte van watter gewas volhoubaar geproduseer kan word met ekonomiese voordele vir die produksiegebied. Dus, WV-bepaling kan gebruik word as hulpmiddel vir bewusmaking, asook vir evaluering van gewas-effektiwiteit tydens besluitneming oor watertoekennings. Verifikasie van FruitLook data met veldmetings, het aangetoon dat die FruitLook platform potensiaal het om gebruik te kan word in besproeiingsbestuursbesluite, wat kan bydra tot verbeterde WUE. Enkele studies is reeds uitgevoer op WUE en blou WV van tafeldruiwe en hierdie studie kan bydra tot die beperkte inligting tans beskikbaar, Meeste studies wat tot op hede gedoen is oor WUE en blou WV van die wingerd in die algemeen en tafeldruiwe spesifiek, was “desktop” studies en het nie werklike plantgroei en fisiologiese metings ingesluit nie. Meeste globale data beskikbaar, tref geen onderskeid tussen die verskillende druiftipes nie (tafeldruiwe, droogdruiwe & wyndruiwe). Deur middel van die direkte plantgebaseerde metings geneem tydens kritiese fenologiese stadia, dra hierdie studie ook by tot die wetenskaplike kennis en begrip van hoe die wingerstok se watergebruik en prestasie beïnvloed word deur verskillende grondtipes en besproeiingstelsels