Determination and modelling of evapotranspiration of bearing and non-bearing apple trees at Grabouw in the Western Cape

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dc.contributor.advisorVan Zyl, J. L.en_ZA
dc.contributor.advisorHoffman, J. E.en_ZA
dc.contributor.authorMeyer, Alineen_ZA
dc.contributor.otherStellenbosch University. Faculty of Agrisciences. Dept. of Soil Science.en_ZA
dc.date.accessioned2024-03-04T20:47:03Z
dc.date.accessioned2024-04-26T21:00:07Z
dc.date.available2024-03-04T20:47:03Z
dc.date.available2024-04-26T21:00:07Z
dc.date.issued2024-03
dc.descriptionThesis (PhDAgric)--Stellenbosch University, 2024. en_ZA
dc.description.abstractENGLISH ABSTRACT: The irrigation of apple trees is important to ensure sustainable production and good quality fruit, especially in regions where rainfall does not contribute adequately to the water demand. Effective scheduling is the key to efficient water use to ensure profitability and sustainability on farms. Quantitative knowledge of the water use and the effect of irrigation application on young apple trees will improve on-farm decision making regarding scheduling. A study was conducted on Malus domestica “Bigbucks‟ (a mutation of “Corder Gala‟) trees grown in a gravelly soil at Grabouw in the Western Cape to determine the effect of three irrigation cycles on the water use, root growth characteristic and tree performance over four growing seasons (October to May) from planting to the first year of bearing. Treatment one (T1) was a short irrigation cycle receiving ca. 15 mm of water per irrigation with an average of 42 irrigations through the growing season, treatment two (T2) was a medium irrigation cycle receiving ca. 27 mm of water with an average of 21 irrigations through the growing season and treatment three (T3) was a long irrigation cycle receiving ca. 37 mm of water with an average of 13 irrigations through the growing season. Crop evapotranspiration (ETC) was determined for all three treatments based on the soil water balance. The ETC of all three treatments increased from the first to the fourth growing season as the leaf area index (LAI) of apple trees increased. T1 had a higher consumptive water use than T2 and T3. Studies done using micro-lysimeters to determine the orchard floor evaporation revealed that T1 lost more water through evaporation compared to T2 and T3, but water loss from the soil mainly occurred through transpiration, irrespective of the treatment. In situ and destructive root studies revealed that both root length density (RLD) and the number of fine roots within the soil profile is strongly related to soil water extraction (SWE). SWE increased with an increase in RLD and the number of fine roots. These results revealed that growing roots can continuously grow into moist regions of the soil. Significantly more fine roots penetrated deeper soil layers and at a greater distance from the tree for the two drier irrigation cycles (T2 and T3). The root index (RI) of T2 and T3 was also higher in deeper soil layers compared to T1 suggesting that soil moisture conditions of T2 and T3 were more favourable in deeper soil layers. It was concluded that short irrigation cycles will favour shallow root growth while longer irrigation cycles promote roots into deeper soil layers. There were no significant differences among treatments in terms of diurnal plant water status, vegetative growth, yield and fruit quality. These results suggest that longer irrigation cycles can be used to save water while simultaneously increasing root growth to deeper soil layers without compromising tree performance. Statistical analysis performed on ETC and RLD data revealed that there is a strong, positive correlation (R² = 0.741) between ETC and RLD. The data was used to develop a statistically significant model in which ETC can accurately be predicted using RLD data or vice versa. The model can be used as a reference for apple producers in South Africa to encourage more precise and effective irrigation scheduling while simultaneously increasing RLD for better water and nutrient uptake resulting in optimal crop production and quality.en_ZA
dc.description.abstractAFRIKAANSE OPSOMMING: Die besproeiing van appelbome is belangrik om volhoubare produksie te verseker en goeie kwaliteit vrugte te produseer, veral in areas waar reënval nie genoegsaam is om te voldoen aan die waterbehoefte van die boom nie. Doeltreffende skedulering is die sleutel tot effektiewe waterverbuik om winsgewendheid en volhoubaarheid op plase te verseker. Kwantitatiewe kennis rakende waterverbuik en die effek van besproeiingtoediening op jong appelbome kan die besluitneming rakende skedulering op plase verbeter. ‘n Studie is gedoen op Malus domestica “Bigbucks” (‘n mutasie van “Corder Gala”) wat in ‘n gruiserige grond by Grabouw in die Wes-Kaap verbou is, om die effek van besproeiingsiklusse op die waterverbruik, wortelgroei en bogrondse boomgroei oor vier groeiseisoene (Oktober tot Mei) vanaf plant tot die eerste jaar van drag, te bepaal. Behandeling een (B1) was ‘n kort besproeiingsiklus wat met gemiddeld 42 toedienings deur die groeiseisoen besproei is met ca. 15 mm water per besproeiing. Behandeling twee (B2) was ‘n medium besproeiingsiklus wat met gemiddeld 21 toedienings deur die groeiseisoen besproei is met ca. 27 mm water per besproeiing. Behandeling drie (B3) was ‘n lang besproeiingsiklus wat met gemiddeld 13 toedienings deur die groeiseisoen besproei is met ca. 37 mm water per besproeiing. Gewas-evapotranspirasie (ETC) is vir al drie behandelings bepaal deur gebruik te maak van die grondwaterbalans. Die ETC van al drie behandelings het toegeneem van die eerste seisoen tot die vierde seisoen as gevolg van die blaararea-indeks wat verhoog het. B1 het ‘n hoër waterverbuik gehad as B2 en B3. Verdamping is bepaal met behulp van mikro-lisimeters en die resultate het getoon dat B1 meer water verloor het deur verdamping in vergelyking met B2 en B3, maar die meeste waterverbruik was as gevolg van transpirasie, ongeag die behandeling. Beide in situ en destruktiewe studies op wortels het aangedui dat daar ‘n sterk verwantskap tussen wortellengte-digtheid (WLD) en grondwater-onttrekking (GWO) is. GWO het toegeneem met ‘n verhoging in beide WLD en die hoeveelheid fyn wortels. Hierdie resultate het aangedui dat wortels voortdurend in klammer areas in die grond kan groei. Beduidend meer fyn wortels het in die dieper grondlae en op ‘n groter afstand vanaf die boom gegroei vir die twee droeër behandelings (B2 en B3). Die wortelindeks (WI) van B2 en B3 was ook hoër in die dieper grondlae in vergelyking met B1 wat aandui dat die grondvog-toestande van B2 en B3 gunstiger in die dieper grondlae was. Daar is tot die gevolgtrekking gekom dat kort besproeiingsiklusse vlak wortelgroei stimuleer, terwyl langer besproeiingsiklusse wortelgroei in dieper grondlae bevorder. Daar was geen betekenisvolle verskille tussen behandelings van daaglikse plantwater-status, vegetatiewe groei, opbrengs en vrugkwaliteit nie. Hierdie resultate dui daarop dat langer besproeiingsiklusse gebruik kan word om water te bespaar en om terselfdertyd wortelgroei na dieper grondlae aan te moedig, sonder om die bogrondse groei te benadeel. Statistiese analises wat op die ETC en WLD data gedoen is, het aangedui dat daar ‘n sterk positiewe verwantskap (R2 = 0.741) tussen ETC en WLD is. Hierdie data is gebruik om ‘n statisties-betekenisvolle model te ontwikkel waarmee ETC akkuraat voorspel kan word, met WLD data of omgekeerd. Die model kan deur appelprodusente in Suid-Afrika as verwysing gebruik word om besproeiing meer presies en effektief te skeduleer en terselfdetyd WLD te verhoog vir beter opname van water en voedingstowwe wat kan lei tot optimale gewasproduksie en -kwaliteit.af_ZA
dc.description.versionDoctorateen_ZA
dc.format.extentxx, 176 pages : illustrations (some color), mapsen_ZA
dc.identifier.urihttps://scholar.sun.ac.za/handle/10019.1/130531
dc.language.isoen_ZAen_ZA
dc.language.isoen_ZAen_ZA
dc.publisherStellenbosch : Stellenbosch Universityen_ZA
dc.rights.holderStellenbosch Universityen_ZA
dc.subject.lcshApples -- Breeding -- South Africa -- Grabouw -- Western Capeen_ZA
dc.subject.lcshApples -- Soils -- South Africa -- Western Capeen_ZA
dc.subject.lcshApples -- Irrigationen_ZA
dc.subject.lcshEvapotranspirationen_ZA
dc.subject.lcshApple trees -- Water requirements -- Grabouw -- Western Capeen_ZA
dc.subject.nameUCTDen_ZA
dc.titleDetermination and modelling of evapotranspiration of bearing and non-bearing apple trees at Grabouw in the Western Capeen_ZA
dc.typeThesisen_ZA
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