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Investigating the effect of soil water constraints at different phenological stages of citrus trees to improve water use efficiency in the Sundays River Valley
Thesis (MScAgric)--Stellenbosch University, 2025.
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Stellenbosch : Stellenbosch University
2025
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| access_status_str | Open Access |
| author | Janse Van Rensburg, Christian |
| author2 | Lategan, E. L. |
| author_browse | Janse Van Rensburg, Christian Lategan, E. L. |
| author_facet | Lategan, E. L. Janse Van Rensburg, Christian |
| author_sort | Janse Van Rensburg, Christian |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Thesis (MScAgric)--Stellenbosch University, 2025. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/134640 |
| institution | Stellenbosch University (South Africa) |
| language | English |
| last_indexed | 2026-06-10T12:46:30.498Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2025 |
| publishDateRange | 2025 |
| publishDateSort | 2025 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
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| spelling | oai:scholar.sun.ac.za:10019.1/134640 Investigating the effect of soil water constraints at different phenological stages of citrus trees to improve water use efficiency in the Sundays River Valley Janse Van Rensburg, Christian Lategan, E. L. Raath, P. J. Stellenbosch University. Faculty of AgriSciences. Dept. of Soil Science. Tango mandarins -- Breeding Deficit irrigation -- South Africa -- Sundays River Valley Plant-water relationships Citrus -- Water requirements -- South Africa -- Sundays River Valley Citrus -- Growth -- Effect of water levels on Citrus -- Effect of temperature on Soil moisture UCTD Thesis (MScAgric)--Stellenbosch University, 2025. Janse Van Rensburg, C. 2025. Investigating the effect of soil water constraints at different phenological stages of citrus trees to improve water use efficiency in the Sundays River Valley. Unpublished masters thesis. Stellenbosch: Stellenbosch University [online]. Available: https://scholar.sun.ac.za/items/d92bdf48-01f9-4b40-8468-df36142b18b2 ENGLISH ABSTRACT: The study was conducted in a semi-arid region to investigate the impact of deficit irrigation strategies on Tango mandarins. Two levels of soil water depletion were applied, namely ca. 20 % depletion of Total Plant Available Water [considered to be non-stressed (NS)] and ca. 80 % depletion of Total Plant Available Water [considered to be water stressed (S)]. By combining the two water depletion levels with the three phenological phases, namely Phase I (cell division), Phase II (cell expansion), and Phase III (maturation). stages eight irrigation treatments. Irrigation was applied by means of drip and micro-sprinkler systems across two seasons (2022/23 and 2023/24). Key objectives included water usage, vegetative and reproductive responses and fruit quality. Due to the variation in the microclimatic conditions under nets compared to open areas, results obtained by means off weather data were also compared. An automatic weather station under nets recorded higher minimum temperatures, relative humidity, and reduced solar irradiance (approximately one-third lower) and wind speed compared to a station 0.9 km away. Reference evapotranspiration (ETo) was lower under nets during summer, but comparable or higher in winter, leading to elevated crop coefficients (Kc) in summer and reduced Kc in winter relative to open conditions. Seasonal average Kc values were lowest in summer, moderate in autumn/spring, and highest in winter. Irrigation volumes were higher in 2023/24 due to increased canopy width (from 3 m to 4 m) and higher ETo (91 mm greater than 2022/23), compounded by substantial rainfall masking treatment effects. Plant water status, measured via leaf (ΨL) and stem (ΨS) water potentials, showed high intra-treatment variability with no clear irrigation-related trends. Leaf area index (LAI) trends were inconsistent; in 2022/23, treatments with early water constraints (Phases I-II) had lower LAI, but no patterns emerged in 2023/24. Micro-sprinkler irrigation promoted greater tree height, canopy volume, and vegetative growth than drip, attributed to larger wetted root zones. Among micro-sprinklers, treatments stressed in Phase I yielded the largest trees; among drip, all-phase stressed treatments resulted in smaller trees. Reproductive parameters generally favoured micro-sprinkler irrigation, which produced more flowers, higher fruit numbers per shoot, and greater fruit set percentages compared with drip irrigation. Phase I stress increased flower counts but reduced fruit set due to elevated physiological fruit drop by late November, which negatively affected yield. No additional fruit drop occurred beyond this period that could be attributed to treatment effects. Fruit growth rates were higher under micro-sprinkler irrigation. Drip-irrigated treatments were more sensitive to early-phase stress, showing reduced early fruit growth that was later compensated when non-stressed irrigation resumed in subsequent phases. At harvest, fruits from micro-sprinkler treatments were generally larger, although no consistent treatment-specific size trends were observed. Fruits from the 2022/23 season were larger overall due to a lower crop load. Yields were higher in micro-sprinkler treatments, driven by larger trees and better fruit set, though alternate bearing caused inter-seasonal variability (higher in 2023/24 despite increased water use). Deficit irrigation in Phase I reduced yields in these drip-irrigated treatments significantly, but effects were inconsistent in micro-sprinkler treatments; Phase III had a negligible imp act. Yield prediction via multiple regression incorporated water use in Phases I-II, fruit count, and size. Production water use efficiency (WUEp) was higher in 2023/24 due to higher yields, but was not consistently enhanced by deficit strategies; all-phase stressed drip achieved highest overall WUEp, while certain micro-sprinkler combinations had the lowest WUEp. Colour development varied seasonally. Uniform colour development in 2022/23 (two harvests), as opposed to more gradual colour development in 2023/24 (three). Drip advanced colouration, harvesting earlier; micro-sprinklers, especially Phase III-stressed, delayed it, possibly due to rainfall. Internal quality showed drip irrigated fruit with higher total soluble solids (TSS) and titratable acidity (TA) than micro-sprinklers, though no consistent treatment effects; sugar:acid ratios and juice content met export standards uniformly. Rainfall likely obscured Phase III constraints. Postharvest, micro-sprinkler fruit exhibited higher rind disorders after storage at -0.6°C and 2°C, with no clear treatment trends; all-phase stressed treatments at -0.6°C and Phase II-stressed at 2°C showed the highest incidences of rind disorders. Pre-storage hydration and dehydration treatments, simulating export handling processes, may have increased fruit susceptibility to rind damage. AFRIKAANSE OPSOMMING: Die studie is in ’n semi-ariede streek uitgevoer om die invloed van tekortbesproeiingstrategieë op Tango-mandaryne te ondersoek. Twee vlakke van grondwateronttrekking is toegepas, naamlik ongeveer 20 % onttrekking van Totale Plantbeskikbare Water [beskou as nie-gestrem (NS)] en ongeveer 80 % onttrekking van Totale Plantbeskikbare Water [beskou as watergestrem (S)]. Deur hierdie twee wateronttrekkingsvlakke met die drie fenologiese fases te kombineer—Fase I (seldeling), Fase II (elselvergroting) en Fase III (ryping)—is agt besproeiingsbehandelings gevorm. Besproeiing is toegepas deur middel van drup- en mikro-sproeiersisteme oor twee seisoene (2022/23 en 2023/24). Sleuteldoelwitte het watergebruik, vegetatiewe en reproduktiewe response, asook vruggehalte ingesluit. Weens variasies in die mikroklimaat onder nette in vergelyking met oop areas, is resultate verkry uit weerdata ook vergelyk. ’n Outomatiese weerstasie onder nette het hoër minimumtemperature, hoër relatiewe humiditeit en laer soninstraling (ongeveer een-derde laer), asook laer windsnelhede aangeteken in vergelyking met ’n stasie 0.9 km weg. Die verwysingsevapotranspirasie (ETo) was laer onder nette gedurende die somer, maar vergelykbaar of hoër in die winter, wat gelei het tot verhoogde gewaskoëffisiënte (Kc) in die somer en verlaagde Kc in die winter relatief tot oop toestande. Seisoenale gemiddelde Kc-waardes was die laagste in die somer, intermediêr in die herfs/lente, en die hoogste in die winter. Besproeiingsvolumes was hoër in 2023/24 weens die toename in blaredakbreedte (van 3 m tot 4 m) en hoër ETo (91 mm meer as 2022/23), verder beïnvloed deur beduidende reënval wat behandelingseffekte gemasker het. Plantwaterstatus, gemeet via blaar- (ΨL) en stamwaterpotensiaal (ΨS), het groot variasie binne behandelings getoon sonder duidelike besproeiingsverwante patrone. Bladoppervlakte-indeks (LAI) het inkonsekwente tendense getoon; in 2022/23 het behandelings met vroeë waterbeperkings (Fases I–II) laer LAI gehad, maar geen duidelike patrone het in 2023/24 ontstaan nie. Mikro-sproeiers het groter boomhoogte, blaredakvolume en vegetatiewe groei bevorder as drupbesproeiing, waarskynlik weens groter benatte wortelsones. Onder mikro-sproeiers het behandelings wat in Fase I gestrem is, die grootste bome opgelewer; onder drup het behandelings wat in alle fases gestrem is, die kleinste bome gelewer. Reproduktiewe parameters het oor die algemeen mikro-sproeiers bevoordeel, wat meer blomme, hoër vruggetalle per loot en groter vrugsetpersentasies gelewer het in vergelyking met drupbesproeiing. Fase I-stremming het blomtalle verhoog, maar vrugset verlaag weens hoër fisiologiese vrugval teen laat November, wat opbrengs negatief beïnvloed het. Geen verdere vrugval is ná hierdie periode waargeneem wat aan behandelingseffekte toegeskryf kon word nie. Vruggroeitempo’s was hoër onder mikro-sproeiers. Drupbehandelings was meer sensitief vir vroeë-fase-stremming en het verlaagde vroeë vruggroei getoon, wat later gedeeltelik gekompenseer is toe nie-gestremde besproeiing in latere fases hervat is. Met oes was vrugte van mikro-sproeierbehandelings oor die algemeen groter, hoewel geen konsekwente behandelingspatrone voorgekom het nie. Vrugte in 2022/23 was oor die algemeen groter weens ’n laer vrugbelasting. Opbrengste was hoër in mikro-sproeierbehandelings, aangedryf deur groter bome en beter vrugset, hoewel alternatiewe dra die interseisoenale variabiliteit beïnvloed het (hoër opbrengste in 2023/24 ten spyte van verhoogde watergebruik). Tekortbesproeiing in Fase I het opbrengste in drupbehandelings aansienlik verlaag, maar het inkonsekwente effekte in mikro-sproeierbehandelings getoon; Fase III het ’n minimale invloed gehad. Opbrengsvoorspelling deur middel van meervoudige regressie het watergebruik in Fases I–II, vruggetal en vruggrootte ingesluit. Produksiewatergebruiksdoeltreffendheid (WUEp) was hoër in 2023/24 weens hoër opbrengste, maar is nie konsekwent verhoog deur tekortstrategieë nie; die drupbehandeling gestrem in alle fases het die hoogste WUEp gelewer, terwyl sekere mikro-sproeierkombinasies die laagste WUEp getoon het. Kleursontwikkeling het tussen seisoene gevarieer. Uniforme kleurontwikkeling is in 2022/23 waargeneem (twee oeste), in teenstelling met ’n meer geleidelike ontwikkeling in 2023/24 (drie oeste). Drup het kleurontwikkeling vervroeg, wat vroeër oes moontlik gemaak het; mikro-sproeiers, veral dié wat in Fase III gestrem is, het dit vertraag, moontlik as gevolg van reënval. Interne gehalte het getoon dat drupbesproeide vrugte hoër totale oplosbare vaste stowwe (TSS) en titreerbare suurheid (TA) gehad het as mikro-sproeiers, hoewel geen konsekwente behandelingspatrone voorgekom het nie; suiker:suur-verhoudings en sapinhoud het deurgaans aan uitvoerstandaarde voldoen. Reënval het waarskynlik Fase III-beperkings gemasker. Ná berging het mikro-sproeier-vrugte ’n hoër voorkoms van skilafwykings getoon by –0.6°C en 2°C, sonder duidelike behandelingspatrone; alle-fase-gestremde behandelings by –0.6°C en Fase II-gestremde behandelings by 2°C het die hoogste voorkoms van skilafwykings gehad. Voorberging-hidrasie en dehidrasieprosedures, wat uitvoerhantering simuleer, het waarskynlik die vatbaarheid van vrugte vir skilskade verhoog. Masters 2025-12-19T13:49:16Z 2025-12-19T13:49:16Z 2025-12 Thesis https://scholar.sun.ac.za/handle/10019.1/134640 en Stellenbosch University xx, 140 pages : illustrations, maps application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Tango mandarins -- Breeding Deficit irrigation -- South Africa -- Sundays River Valley Plant-water relationships Citrus -- Water requirements -- South Africa -- Sundays River Valley Citrus -- Growth -- Effect of water levels on Citrus -- Effect of temperature on Soil moisture UCTD Janse Van Rensburg, Christian Investigating the effect of soil water constraints at different phenological stages of citrus trees to improve water use efficiency in the Sundays River Valley |
| title | Investigating the effect of soil water constraints at different phenological stages of citrus trees to improve water use efficiency in the Sundays River Valley |
| title_full | Investigating the effect of soil water constraints at different phenological stages of citrus trees to improve water use efficiency in the Sundays River Valley |
| title_fullStr | Investigating the effect of soil water constraints at different phenological stages of citrus trees to improve water use efficiency in the Sundays River Valley |
| title_full_unstemmed | Investigating the effect of soil water constraints at different phenological stages of citrus trees to improve water use efficiency in the Sundays River Valley |
| title_short | Investigating the effect of soil water constraints at different phenological stages of citrus trees to improve water use efficiency in the Sundays River Valley |
| title_sort | investigating the effect of soil water constraints at different phenological stages of citrus trees to improve water use efficiency in the sundays river valley |
| topic | Tango mandarins -- Breeding Deficit irrigation -- South Africa -- Sundays River Valley Plant-water relationships Citrus -- Water requirements -- South Africa -- Sundays River Valley Citrus -- Growth -- Effect of water levels on Citrus -- Effect of temperature on Soil moisture UCTD |
| url | https://scholar.sun.ac.za/handle/10019.1/134640 |
| work_keys_str_mv | AT jansevanrensburgchristian investigatingtheeffectofsoilwaterconstraintsatdifferentphenologicalstagesofcitrustreestoimprovewateruseefficiencyinthesundaysrivervalley |