Quantifying water movement in soils irrigated by continuous drip irrigation with citrus in the Western Cape

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dc.contributor.advisorHoffman, Eduarden_ZA
dc.contributor.advisorRaath, Pieteren_ZA
dc.contributor.authorvan der Merwe, Johan Herbsten_ZA
dc.contributor.otherStellenbosch University. Faculty of AgriSciences. Dept. of Soil Science.en_ZA
dc.date.accessioned2022-02-28T10:38:27Z
dc.date.accessioned2022-04-29T09:31:46Z
dc.date.available2022-02-28T10:38:27Z
dc.date.available2022-04-29T09:31:46Z
dc.date.issued2022-04
dc.descriptionThesis (MScAgric)--Stellenbosch University, 2022.en_ZA
dc.description.abstractENGLISH ABSTRACT: The development of low discharge rate emitters by Netafim opened new possibilities to approach irrigation and fertilization and introduced continuous low flow drip irrigation, allowing for intensive management of fruit production on difficult to manage soils. This entails decreasing the application rate of the irrigation system to balance with the maximum daily water use over the total consumptive period of the crop addressing many challenges in managing irrigation in an orchard. A key for efficient drip irrigation is to adjust the shape of the wetted soil volume created under an emitter to the main root distribution, which is well known for conventional drippers in different soil types, but not for low flow continuous drip irrigation. In this study the daily water requirement of young ‘Nadorcott’ mandarin citrus trees were applied in three continuous drip irrigation treatments with different drip discharge rates (T1-0.4L.hˉ¹, T2-0.7L.hˉ¹ and T3-1.6L.hˉ¹ allowing different irrigation cycle lengths, to study the effect on soil water content distribution, root distribution and crop response . T1-0.4L.hˉ¹ maintained an average higher SWC in the active root zone along the season followed by T2-0.7L.hˉ¹ and T3-1.6L.hˉ¹ respectively. Significantly higher SWC was observed close to the soil surface with T1-0.4L.hˉ¹ followed by T2-0.7L.hˉ¹ and T3-1.6L.hˉ¹ respectively. Relative average lower SWC with daily conventional irrigation was expected due to narrower spacing of drippers and lower volume of water applied per emitter. 2-Dimentional water distribution patterns parallel and across the ridge showed that T1- 0.4L.h resulted in a smaller wetted soil volume compared to T2-0.7L.h with less horizonal and vertical water distribution from an emitter, which may have encouraged fibrous roots to grow closer to the soil surface and to the tree. More overlap was observed in T2-0.7L.h parallel with the ridge resulting in greater vertical distribution of water between two adjacent drippers where wetted soil volumes merge which favoured roots to grow and proliferate deeper down the soil profile and further away from the tree. A wetted strip was formed under T3-1.6L.h due to narrower spacing of drippers, compared to the ‘pots’ formed with T1-0.4l.h and T2-0.7L.h, resulting in a dense root strip across the profile in the 20 to 40cm depth. Highest fine root density was recorded in T3-1.6L.h in the 20 -30 cm layer, followed by T2-0.7L.h in the 30 to 40 cm layer and T1-0.4L.h in the 20-30 cm layer respectively. A bimodal distribution of water was observed in T1-0.4L.h and T2-0.7L.h early in the morning when a shorter irrigation event took place characterized by a main wetted soil volume in the upper 50 cm and concentrated areas of higher soil water content in the lower 50 cm. Approaching midday as irrigation continued SWC in the main core of the wetted soil volume increased and lower SWC was observed in the rest of the soil profile indicating a ‘shrinking’ of the wetted bulb midday after which a bimodal water distribution resumed. T3- 1.6 showed very little fluctuation during the day. It seems as if the antecedent soil water content may contribute largely to soil water content fluctuation and distribution patterns. Overall little fluctuation of the wetted soil volume was observed daily, maintaining very constant SWC levels in the root zone.en_ZA
dc.description.abstractAFRIKAANSE OPSOMMING: Die ontwikkeling van lae lewering druppers deur Netafim het nuwe moontlikhede mee gebring om besproeing en bemesting deur die dripstelsels te benader en het deurlopende lae vloei drupbesproeing bekendgestel aan landbou wat intensiewe bestuur van gewasproduksie op voorheen moeilik bestuurbare grond vir besproeing moontlik maak. Hierdie konsep behels om die lewering van die besproeingstelsel te verlaag om te balenseer met die maksimum daaglikse waterverbruik oor die totale waterverbruiksperiode van die gewas, wat vele uitdagings van besproeingsbestuur van ‘n boord aanspreek. ‘n Sleutel tot effektiewe drupbesproeing is om die vorm van die benatte grond volume wat onder ‘n drupper vorm so te bestuur om ooreen te stem met die hoof wortelverspreiding, wat wel bekend is vir tradisionele hoër lewering druppers, maar nie vir deurlopende lae vloei drupbesproeing nie. In hierdie studie was die daaglikse water behoefte van jong ‘Nadorcott’ sitrus bome toegedien deur drie deurlopende drupbesproeing behandelings met verskillende drup lewering (T1-0.4L.hˉ¹, T2-0.7L.hˉ¹ en T3-1.6L.hˉ¹) wat drie bespoeingsikluslengtes toegelaat het om die effek op grondwaterinhoudsverspreiding, wortelverspreiding en gewasreaksie te ondersoek. T1-0.4L.hˉ¹ het ‘n gemiddelde hoër grondwaterinhoud in die aktiewe wortelsone gehandhaaf met die verloop van die seisoen gevolg deur T2-0.7L.hˉ¹ en T3- 1.6L.hˉ¹onderskeidelik. Beduidende hoër grondwaterinhoud was nader aan die grondoppervlak geobserveer met T1-0.4L.hˉ¹ gevolg deur T2-0.7L.hˉ¹ en T3- 1.6L.hˉ¹onderskeidelik. Relatiewe laer gemiddelde grondwaterinhoud met T3-1.6L.hˉ¹ was verwag asgevolg van die nader spasiering van druppers en laer volume water wat per drupper, toegedien word. 2- Dimensionele waterverspreidingspatrone parallel and loodreg met die rif het aangetoon dat T1-0.4L.hˉ¹ ‘n kleiner benatte grondvolume tot gevolg gehad het in vergelyking met T2-0.7L.hˉ¹ met minder horisontale waterverspreiding vanaf ‘n drupper, wat fynwortels kon aangemoedig het om nader aan die grondoppervlak en die boom te groei. ‘n Groter mate van oorvleuel van benatte grondvolumes parallel met die rif was geobserveer met T2-0.7L.hˉ¹ wat gelei het tot meer vertikale verspreiding van water waar benatte grond volumes oorvleuel het, wat wortel aangemoedig het om dieper in die grond profiel te groei en verder weg vanaf die boom te versprei. ‘n Benatte strook het gevorm met T3-1.6L.hˉ¹ asgevolg van die nader spasiering van druppers, in vergelyking met die benatte ‘potte’ wat gevorm het met T1-0.4L.hˉ¹ en T2-0.7L.hˉ¹, wat gelei het tot ‘n wortelstrook regoor die profiel tussen aangrensende bome in die 20 tot 40 cm diepte. Hoogste fynworteldigtheid was geobserveer met T3-1.6L.hˉ¹ in die 20-30 cm laag, gevolg deur T2-0.7L.hˉ¹ in die 30-40cm laag en T1-0.4L.hˉ¹ in die 20-30 cm laag onderskeidelik. ‘n Bimodale waterversreiding was waargeneem in T1-0.4L.hˉ¹ en T2-0.7L.hˉ¹ vroeg in die oggend met die aanloop van’n ‘korter’ beproeing siklus, met ‘n hoof benatte grondvolume in die boonste 50 cm and gekonsentreerde areas van hoër grondwaterinhoud in die onderste 50 cm. Met die aanloop na middag soos besproeing verloop het, het die grondwaterinhoud in die ‘kern’ van die hoof benatte grondvolume toegeneem en laer grondwaterinhoud was in die res van die profiel opgemerk wat ‘ krimping’ van die benatte grondvolume toon oor middag. Soos die dag verloop het was ‘n bimodale verspreding van water weer waargeneem na middag. T3-1.6L.hˉ¹ het baie min verandering gedurende die dag getoon. Dit bleik dat voorafgaande grondwate inhoud voor ‘n besproeingsiklus begin moontlik ‘n groot effek het op grondwater fluktuasie en waterverspreidingspatrone. Oor die algemeen was die daaglikse verandering in grondwaterinhoud minimaal met al drie behandelinge en het konstante hoë grondwaterinhoud vlakke in die wortel sone gehandhaaf.af_ZA
dc.description.versionMastersen_ZA
dc.format.extent142 pages : illustrations (some color)en_ZA
dc.identifier.urihttp://hdl.handle.net/10019.1/124772
dc.language.isoen_ZAen_ZA
dc.publisherStellenbosch : Stellenbosch Universityen_ZA
dc.rights.holderStellenbosch Universityen_ZA
dc.subjectCitrus -- Growthen_ZA
dc.subjectDrip irrigationen_ZA
dc.subjectCitrus -- Irrigationen_ZA
dc.subjectSoils, Irrigated -- South Africa -- Western Capeen_ZA
dc.subjectCitrus -- Rootstocksen_ZA
dc.subjectSoil moisture -- South Africa -- Western Cape -- Measurement -- Mathematical modelsen_ZA
dc.subjectUCTDen_ZA
dc.titleQuantifying water movement in soils irrigated by continuous drip irrigation with citrus in the Western Capeen_ZA
dc.typeThesisen_ZA
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