Establishing the water requirements and crop coefficients of a mature mango orchard under subtropical conditions
| dc.contributor.advisor | Sebinasi, Dzikiti | en_ZA |
| dc.contributor.advisor | Kleinert, Aleysia | en_ZA |
| dc.contributor.author | George, Nel | en_ZA |
| dc.contributor.other | Stellenbosch University. Faculty of Agrisciences. Dept. of Horticulture. | en_ZA |
| dc.date.accessioned | 2024-03-07T10:51:03Z | |
| dc.date.accessioned | 2024-04-26T10:15:41Z | |
| dc.date.available | 2024-03-07T10:51:03Z | |
| dc.date.available | 2024-04-26T10:15:41Z | |
| dc.date.issued | 2024-03 | |
| dc.description | Thesis (MScAgric)--Stellenbosch University, 2024. | en_ZA |
| dc.description.abstract | ENGLISH ABSTRACT: The study was done in the Inkomati - Usuthu Water Management Area (IUWMA) in north - eastern South Africa. The region is a prime production area for a range of crops, mostly subtropical tree crops (banana, citrus, litchi, macadamia, mango etc.) and sugarcane, mainly under irrigation. Yet water resources in the catchment are almost fully allocated due to the rising competition between various water use sectors e.g. agriculture, industrial development, eco-tourism etc. The increasing frequency and severity of droughts due to climate change are exacerbating the problem, so there is a need for accurate water management practices to maximize crop production per drop of water. The goal of this study was to establish the maximum water requirements of mango orchards to improve the management of scarce water resources in the catchment. The focus was also on generating information on how water use related to the yield of mango orchards under local growing conditions. To support economic development in the catchment, the IUWMA plans to implement Water Allocation Reforms (WAR) to provide fair access to water to various water users in the catchment and to fulfil the requirements of the National Water Act of South Africa (of 1998). Implementation of these reforms requires accurate quantitative information on the water use of key irrigated crops like mango and other tree crops. In this study, we used state-of-the-art methods to measure the actual water use of mango orchards, collecting detailed data on the soil-plant-atmosphere interactions over close to two growing seasons. Data were collected at the leaf level using infrared gas analysers while whole tree transpiration rates were quantified using the heat ratio sap flow method. An open path eddy covariance system was used to measure the whole orchard evapotranspiration rates. To ensure that the results obtained from the specific study orchard can be transferred to mango orchards elsewhere, we used the measured data to test and compare the performance of two independent models of estimating orchard water use. Key findings from the study are that firstly, based on detailed leaf gas exchange measurements, mango trees have significant stomatal and non - stomatal limitations to net CO2 assimilation. The trees are predominantly isohydric in nature, closing their stomata under unfavourable environmental conditions, e.g. excessive atmospheric evaporative demand, soil water deficit, etc. This, in turn affects their transpiration rates. The observed maximum net CO2 assimilation rate for well-watered trees under clear sky conditions was less than 6.0 μmol/m²/s. This is substantially lower than that of other irrigated fruit tree crops reported in literature. Secondly, the daily maximum transpiration of a fully grown mango tree (leaf area index between 3.3 and 3.7) ranged between 40 and 62 litres of water per tree per day depending on canopy size and weather conditions. The measured annual total transpiration was about 601 mm (or 6 010 m³/ha/y), while the annual evapotranspiration predicted by the water use models ranged from 880 to 910 mm/y (or 8 800 to 9 100 m³/ha/y). The farm scheduled their irrigation using a crop coefficient of 1.0 during the entire irrigation season. However, this study showed that the actual crop coefficient was not constant; it varied between 0.75 and 0.93 depending on the crop growth stage. This highlighted an opportunity for significant water savings if the correct crop coefficients are used. Lastly, but also quite significantly, this study modified and improved an approach for deriving both the crop coefficients and basal crop coefficients for mango orchards using readily available data such as the average tree height and the fractional vegetation cover. This approach will allow mango growers to obtain accurate estimates of crop coefficients for their orchards depending on their specific conditions e.g. tree age, soil type, irrigation system, cover crop status, etc. These and other findings are summarized in a manuscript that is currently in the second round of review by the Scientia Horticulture journal. | en_ZA |
| dc.description.abstract | AFRIKAANSE OPSOMMING: Die studie is in die Inkomati-Usuthu Waterbestuursgebied (IUWMA) in noord-oostelike Suid-Afrika gedoen. Die streek is 'n uitstekende produksiegebied vir 'n reeks gewasse, meestal subtropiese boomgewasse (piesang, sitrus, lietsjie, makadamia, mango ens.) sowel as suikerriet, die gewasse word hoofsaaklik onder besproeiing verbou. Tog word waterbronne in die opvanggebied amper ten volle toegewys as gevolg van die toenemende mededinging tussen verskeie watergebruiksektore. Water alokasie word tussen die volgende gebruiksektore gesplit: landbou, nywerheidsontwikkeling, ekotoerisme, ens. Die toenemende frekwensie en erns van droogtes as gevolg van klimaatsverandering vererger die probleem, dus is daar 'n behoefte aan akkurate waterbestuurspraktyke om gewasproduksie per druppel water te maksimeer. Die doel van hierdie studie was om die maksimum watervereistes van ‘n mangoboorde vas te stel om die bestuur van skaars waterbronne in die opvanggebied te verbeter. Die fokus was ook op die generering van inligting oor hoe watergebruik verband hou met die opbrengs van mangoboorde onder plaaslike groeitoestande. Om ekonomiese ontwikkeling in die opvanggebied te ondersteun, beplan die IUWMA om Watertoewysingshervormings (WAR) te implementeer om doeltrevende toegang tot water aan verskeie watergebruikers in die opvanggebied te verskaf en om aan die vereistes van die Nasionale Waterwet van Suid-Afrika (van 1998) te voldoen. Implementering van hierdie hervormings vereis akkurate kwantitatiewe inligting oor die watergebruik van sleutelbesproeiingsgewasse soos mango en ander boomgewasse. In hierdie studie het ons moderne metodes gebruik om die werklike watergebruik van mango-boorde te meet, deur gedetailleerde data oor die grond-plant-atmosfeer- interaksies oor byna twee groeiseisoene in te samel. Data is op blaarvlak ingesamel deur gebruik te maak van infrarooi gas ontleders terwyl heelboom transpirasietempo's gekwantifiseer is deur die hitteverhouding sapvloeimetode te gebruik. 'n Ooppad-wervel-kovariansiestelsel is gebruik om die hele boord-evapotranspirasietempo's te meet. Om te verseker dat die resultate wat van die spesifieke studieboord verkry is, na mango-boorde elders oorgedra kan word, het ons die gemete data gebruik om die prestasie van twee onafhanklike modelle van die skatting van boordwatergebruik te toets en te vergelyk. Sleutelbevindinge van die studie is dat mangobome eerstens, gebaseer op gedetailleerde blaargaswisselingsmetings, beduidende stomatale en nie-stomatale beperkings tot netto CO2 assimilasie het. Die bome is oorwegend isohidries van aard, wat hul huidmondjies toemaak onder ongunstige omgewingstoestande, bv. oormatige atmosferiese verdampingsaanvraag, grondwatertekort, ens. Dit beïnvloed weer hul transpirasietempo's. Die waargenome maksimum netto CO2 assimilasietempo vir goed natgemaakte bome onder helder lugtoestande was minder as 6.0 mol/m²/s. Dit is aansienlik laer as dié van ander besproeide vrugteboomgewasse wat in literatuur gerapporteer word. Tweedens het die daaglikse maksimum transpirasie van 'n volgroeide mangoboom (blaaroppervlak-indeks tussen 3,3 en 3,7) tussen 40 en 62 liter water per boom per dag gebruik, afhangende van blaredakgrootte en weerstoestande. Die gemiddelde jaarlikse totale transpirasie was ongeveer 601 mm (of 6 010 m³/ha/j), terwyl die jaarlikse evapotranspirasie wat deur die watergebruiksmodelle voorspel is van 880 tot 910 mm/j (of 8 800 tot 9 100 m³/ha/j) gewissel het. Die plaas het hul besproeiing geskeduleer deur 'n gewaskoëffisiënt van 1.0 gedurende die hele besproeiingseisoen te gebruik. Hierdie studie het egter getoon dat die werklike oeskoëffisiënt nie konstant was nie; dit het tussen 0,75 en 0,93 gewissel na gelang van die gewasgroeistadium. Dit het 'n geleentheid vir aansienlike waterbesparing uitgelig as die korrekte gewaskoëffisiënte gebruik word. Laastens, maar ook aansienlik, het hierdie studie 'n benadering vir die afleiding van beide die gewaskoëffisiënte en basale gewaskoëffisiënte vir mango-boorde gewysig en verbeter deur gebruik te maak van geredelik beskikbare data soos die gemiddelde boomhoogte en die fraksionele plantegroeibedekking. Hierdie benadering sal mangoprodusente in staat stel om akkurate skattings van gewaskoëffisiënte vir hul boorde te verkry na gelang van hul spesifieke toestande bv. boomouderdom, grondtipe, besproeiingstelsel, dekgewasstatus, ens. Hierdie en ander bevindinge word saamgevat in 'n manuskrip wat tans in die tweede rondte van hersiening deur die Scientia Horticulture-joernaal is. | af_ZA |
| dc.description.version | Masters | en_ZA |
| dc.format.extent | vii, x, 105 pages : illustrations (some color), maps | en_ZA |
| dc.identifier.uri | https://scholar.sun.ac.za/handle/10019.1/130236 | |
| dc.language.iso | en_ZA | en_ZA |
| dc.language.iso | en_ZA | en_ZA |
| dc.publisher | Stellenbosch : Stellenbosch University | en_ZA |
| dc.rights.holder | Stellenbosch University | en_ZA |
| dc.subject.lcsh | Watersheds -- South Africa -- Inkomati - Usuthu Water Management Area | en_ZA |
| dc.subject.lcsh | Mango -- Growth | en_ZA |
| dc.subject.lcsh | Orchards -- Management | en_ZA |
| dc.subject.lcsh | Fruit trees -- Effect of temperature on | en_ZA |
| dc.subject.lcsh | Plants -- Water requirements | en_ZA |
| dc.subject.lcsh | Evapotranspiration -- South Africa -- Measurement | en_ZA |
| dc.subject.lcsh | Soil moisture | en_ZA |
| dc.subject.name | UCTD | en_ZA |
| dc.title | Establishing the water requirements and crop coefficients of a mature mango orchard under subtropical conditions | en_ZA |
| dc.type | Thesis | en_ZA |
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