Evaluating the effect of low flow drip irrigation on selected growth parameters of citrus trees

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dc.contributor.advisorHoffman, Josias Eduarden_ZA
dc.contributor.advisorRaath, Pieter Johannesen_ZA
dc.contributor.authorPretorius, Johannes Jacoben_ZA
dc.contributor.otherStellenbosch University. Faculty of Agrisciences. Dept. of Soil Science.en_ZA
dc.date.accessioned2023-03-07T14:58:20Z
dc.date.accessioned2023-05-18T07:09:32Z
dc.date.available2023-03-07T14:58:20Z
dc.date.available2023-05-18T07:09:32Z
dc.date.issued2023-03
dc.descriptionThesis (MScAgric)--Stellenbosch University, 2023. en_ZA
dc.description.abstractENGLISH ABSTRACT: The use of low flow drip irrigation is preferred nowadays in South Africa due to easier irrigation management, increased ability of precision irrigation and claims of increased water-use efficiency. The aim of the study was to investigate the validity of such claims since there is mounting pressure for all industries to find new methods to save water. Furthermore, it is imperative to investigate the effect that any new irrigation method has on both the soil environment and plant productivity. This study investigated the performance of three different drip delivery rate treatments (T1-1.6 L.h⁻¹, T2-0.7 L.h⁻¹ and T3-0.4 L.h⁻¹) with regards to soil water content (SWC) distribution, soil electrical conductivity and pH distribution, water-use efficiency, tree stress, fruit yield and quality. The soil water content distribution showed that the use of pulsed irrigation with a higher emission rate such as T1-1.6 L.h⁻¹ was most successful in preventing the movement of water out of the active rootzone, followed by T3-0.4 L.h⁻¹ and T2-0.7 L.h⁻¹. For T3-0.4 L.h⁻¹ it was concluded that the application rate was very similar to the overall uptake rate of the trees since there was also a reduced movement of water beyond the active root zone and very small changes in the water content of the main wetted core even as irrigation was applied. The higher application rate of T2-0.7 L.h⁻¹, compared to T3-0.4 L.h⁻¹ led to a greater degree of water movement beyond the active root zone. The calculated water-use efficiencies showed very good agreement with the measured SWC distributions since T1- 1.6 L.h⁻¹ had the highest water-use efficiency, followed by T3-0.4 L.h⁻¹ and T2-0.7 L.h⁻¹ respectively. The electrical conductivity showed good agreement with the soil water distributions since there was an increase in salts at the periphery of the wetted volumes; this became more prominent as the drip delivery rate decreased. All treatments showed severe acidification directly beneath the drippers which was ascribed to the form and quantity of nitrogen that was applied to the trees. The predawn leaf and midday stem water potential measurements taken during the main phenological phases of fruit growth during the 2022 production season concluded that no single treatment was constantly subject to more stress compared to the other. The results did however indicate that all treatments displayed symptoms similar to trees that only have a fraction of the root zone exposed to sufficient water content ranges. Considering the results already discussed, it could be concluded that the availability of soil water to the plants was not only influenced by the physical distribution thereof, but it was also less available due to chemical constraints. The fruit yield of the 2021 production season was mainly influenced by differences in the applied irrigation volumes with T1-1.6 L.h⁻¹ having the highest yield, followed by T2-0.7 L.h⁻¹ and T3-0.4 L.h⁻¹ respectively. Alternate bearing also seemed to have played a role in the yield differences observed for the 2021 and 2022 production seasons. The yield of the 2022 production season was mainly affected by tree physiology and T1-1.6 L.h⁻¹ again had the highest yield, followed by T3-0.4 L.h⁻¹ and T2-0.7 L.h⁻¹ respectively. Overall, the fruit quality was always at acceptable export levels for all treatments.en_ZA
dc.description.abstractAFRIKAANSE OPSOMMING: Die gebruik van laevloei-drupbesproeiing word deesdae in Suid-Afrika verkies weens makliker besproeiingsbestuur, verbeterde presisiebesproeiing en bewerings van verhoogde waterverbruiksdoeltreffendheid. Die doel van die studie was om die geldigheid van sulke bewerings te ondersoek, aangesien daar toenemende druk op alle industrië is om nuwe metodes te vind om water te bespaar. Verder is dit noodsaaklik om ondersoek in te stel na die effek wat enige nuwe besproeiingsmetode op beide die grondomgewing en plantproduktiwiteit sal hê. Hierdie studie het die effek van drie verskillende drupleweringstempo’s (T1-1.6 L.h-1, T2-0.7 L.h-1 en T3-0.4 L.h-1) met betrekking tot die verspreiding van grondwaterinhoud, grondelektriesegeleidingsvermoë en pH ondersoek. Verder was daar ook ondersoek ingestel na die effek van die behandelings op waterverbruiksdoeltreffendheid, boomstres, vrugopbrengs en vrugkwaliteit. Die grondwaterinhoudsverspreidings het getoon dat die gebruik van pulsbesproeiing met 'n hoër leweringstempo soos T1-1.6 L.h⁻¹, die suksesvolste was om die beweging van water uit die aktiewe wortelsone te beperk, gevolg deur T3-0.4 L.h-1 en T2-0.7 L.h-1 onderskeidelik. Die berekende waterverbruiksdoeltreffendheid het `n baie goeie ooreenstemming met die gemete grondwaterverspreidings getoon, aangesien T1-1.6 L.h-1 die hoogste waterverbruiksdoeltreffendheid gehad het, gevolg deur T3-0.4 L.h-1 en T2-0.7 L.h-1 onderskeidelik. Die verspreiding van elektriesegeleidingsvermoë het goeie ooreenstemming met die grondwaterverspreidings getoon aangesien daar 'n toename in soute aan die periferie van die benatte volumes was. Hierdie verskynsel het meer prominent geword namate die drupleweringstempo afgeneem het. Alle behandelings het ernstige versuring direk onder die druppers getoon wat toegeskryf word aan die vorm en hoeveelheid stikstof wat tot die bome toegedien was. Die voor-dag blaarwaterpotensiaal en middag stamwaterpotensiaal metings wat tydens die hoof fenologiese fases van vruggroei gedurende die 2022-produksieseisoen geneem is, het getoon dat geen enkele behandeling voortdurend onderhewig was aan meer stres in vergelyking met die ander nie. Die resultate het egter aangedui dat alle behandelings simptome getoon het wat soortgelyk was aan bome waarvan slegs 'n fraksie van die wortelsone blootgestel is aan voldoende grondwaterinhoude. Met inagneming van die resultate wat reeds bespreek is, kan die gevolgtrekking gemaak word dat die beskikbaarheid van grondwater aan die bome nie net deur die fisiese verspreiding daarvan beïnvloed was nie, maar dat dit ook minder beskikbaar was weens chemiese beperkings. Die vrugopbrengs van die 2021-produksieseisoen was hoofsaaklik beïnvloed deur verskille in die toegediende besproeiingsvolumes met T1-1,6 L.h-1 wat die hoogste opbrengs gelewer het, gevolg deur T2-0,7 L.h-1 en T3-0,4 L.h-1 onderskeidelik. Alternatiewe drag het ook 'n rol gespeel in die opbrengsverskille wat vir die 2021- en 2022-produksieseisoene waargeneem is. Die opbrengs van die 2022-produksieseisoen is hoofsaaklik deur boomfisiologie beïnvloed en T1-1,6 L.h-1 het weer die hoogste opbrengs gehad, gevolg deur T3-0,4 L.h-1 en T2-0,7 L.h-1 onderskeidelik. Oor die algemeen was die vrugkwaliteit van elke behandeling altyd op aanvaarbare uitvoervlakke.af_ZA
dc.description.versionMastersen_ZA
dc.format.extent147 pages : illustrations (some color), mapsen_ZA
dc.identifier.urihttp://hdl.handle.net/10019.1/127202
dc.language.isoen_ZAen_ZA
dc.publisherStellenbosch : Stellenbosch Universityen_ZA
dc.rights.holderStellenbosch Universityen_ZA
dc.subject.lcshMicroirrigation -- South Africaen_ZA
dc.subject.lcshWater efficiencyen_ZA
dc.subject.lcshDrip irrigation -- Evaluationen_ZA
dc.subject.lcshCitrus -- Breedingen_ZA
dc.subject.lcshCitrus -- Water requirementsen_ZA
dc.subject.lcshSoil water content -- Measurementen_ZA
dc.subject.nameUCTDen_ZA
dc.titleEvaluating the effect of low flow drip irrigation on selected growth parameters of citrus treesen_ZA
dc.typeThesisen_ZA
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