The effect of invasive alien plants (IAPs) biochar properties on soil quality and crop production

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dc.contributor.advisorHardie-Pieters, Ailsa G.en_ZA
dc.contributor.advisorSwanepoel, Pieter Andreasen_ZA
dc.contributor.authorMncedi, Siphoen_ZA
dc.contributor.otherStellenbosch University. Faculty of Agrisciences. Dept. of Soil Science.en_ZA
dc.date.accessioned2024-02-13T07:11:42Z
dc.date.accessioned2024-04-27T01:00:25Z
dc.date.available2024-02-13T07:11:42Z
dc.date.available2024-04-27T01:00:25Z
dc.date.issued2024-03
dc.descriptionThesis (MScAgric)--Stellenbosch University, 2024. en_ZA
dc.description.abstractENGLISH ABSTRACT: Woody invasive alien plants (IAPs), such as black wattle (Acacia mearnsii) and eucalypt (Eucalyptus camaldulensis), are a major problem in South Africa. IAPs can decrease surface water runoff and groundwater recharge and are actively being cleared on a large scale. The woody biomass generated from the clearing of IAPs can serve as feedstock for biochar production. By sequestering carbon and improving soil functions, biochar has shown promise for enhancing agricultural practices. The efficacy of biochar in enhancing soil quality and crop production varies widely depending on its properties which are influenced by the type of feedstock and pyrolysis conditions used. According to the literature, biochar can contain certain toxic compounds such as heavy metals and volatile organic compounds formed during pyrolysis. Therefore, it is critical to test biochars on intended soils and crops to select the most suitable biochars. The aim of this study was to investigate the effect of fresh and aged biochars produced from IAPs from different feedstocks and pyrolysis temperatures on soil quality and crop production. Five biochars were produced at a range of temperatures (500, 600, 700, and 800 °C) from eucalypt and a single temperature (600 °C) from black wattle biomass using low-vacuum pyrolysis. In June 2022, the biochars were applied at 1.5% (w/w) on acid sandy soil and cauliflower was cultivated in an optimally fertilized greenhouse experiment. Some of the soil-biochar mixtures were left outside for 11 months so that the biochar could age naturally in the soil. After 11 months of ageing, the cauliflower greenhouse experiment was repeated using the same cauliflower cultivar and experimental conditions. In both trials (fresh and aged biochar trial), soil chemical, physical and microbiological properties were determined at planting and harvest. At harvest, the cauliflower fresh and oven-dried curd, and above-ground biomass were determined. The oven-dried curd and leaves were analysed for total elemental macro and micronutrient analysis (N, P, S, Ca, Mg, K, Na, Fe, Mn, Cu, Zn and B). In the fresh biochar trial, the 600 °C eucalypt biochar had the most positive effect on cauliflower yields (53% increase), attributed to higher soil basic cation exchange capacity and N retention. Whereas the higher temperature (700 and 800 °C) eucalypt and 600 °C black wattle biochars suppressed crop yields by 26-79% attributed to phytotoxicity, alkalinity, and reduction of B and soil water availability. All fresh biochars were found to reduce total available water due to high microporosity. Whereas in the aged biochar trial, only low-temperature eucalypt biochar (500 °C) suppressed the total available water. Biochar ageing reduced soil total N, but slightly increased effective cation exchange capacity and easily available water content however not compared to the aged sand control. The ageing of eucalypt and black wattle biochar also seemed to reduce the phytotoxicity that was present in certain fresh biochars. However, none of the aged biochars had a significant effect on cauliflower yields compared to the control sand. The results of this study highlight the importance of biochar properties, as influenced by pyrolysis conditions and feedstock, on crop growth response.en_ZA
dc.description.abstractAFRIKAANSE OPSOMMING: Houtagtige uitheemse indringerplante (UIP), soos swartwattel (Acacia mearnsii) en bloekom (Eucalyptus camaldulensis), is 'n groot probleem in Suid-Afrika. UIP kan oppervlakwaterafloop en grondwateraanvulling verminder en word aktief op groot skaal skoongemaak. Die houtagtige biomassa wat uit die skoonmaak van UIP gegenereer word, kan as grondstof vir biochar-produksie dien. Deur koolstof te sekwestreer en grondfunksies te verbeter, het biochar belofte getoon vir die verbetering van landboupraktyke. Die doeltreffendheid van biochar in die verbetering van grondkwaliteit en gewasproduksie wissel grootliks na gelang van sy eienskappe wat beïnvloed word deur die tipe grondstof en pirolise toestande wat gebruik word. Volgens die literatuur kan biochar sekere giftige verbindings bevat soos swaar metale en vlugtige organiese verbindings wat tydens pirolise gevorm word. Daarom is dit van kritieke belang om biochars op beoogde gronde en gewasse te toets om die mees geskikte biochars te kies. Die doel van hierdie studie was om die effek van vars en verouderde biochars geproduseer uit UIP van verskillende grondstowwe en pirolise temperature op grondkwaliteit en gewasproduksie te ondersoek. Vyf biochars is geproduseer teen 'n reeks temperature (500, 600, 700 en 800 °C) vanaf bloekom en 'n enkele temperatuur (600 °C) uit swartwattelbiomassa met behulp van laevakuum-pirolise. In Junie 2022 is die biochars teen 1.5% (w/w) op suur sandgrond toegedien en blomkool is verbou in 'n optimaal bemeste kweekhuiseksperiment. Van die grond-biochar-mengsels is vir 11 maande buite gelaat sodat die biochar natuurlik in die grond kon verouder. Na 11 maande van veroudering is die blomkoolkweekhuiseksperiment herhaal met dieselfde blomkoolkultivar en eksperimentele toestande. In beide proewe (vars en verouderde biokoolproef) is grondchemiese, fisiese en mikrobiologiese eienskappe tydens plant en oes bepaal. Met oes is die blomkool vars en oondgedroogde wrongel, en bogrondse biomassa bepaal. Die oondgedroogde wrongel en blare is ontleed vir totale elementêre makro- en mikronutriëntanalise (N, P, S, Ca, Mg, K, Na, Fe, Mn, Cu, Zn en B). In die vars biokoolproef het die 600 °C bloekombiokool die mees positiewe effek op blomkoolopbrengste (53% toename), toegeskryf aan hoër grond basiese katioonuitruilkapasiteit en N retensie. Terwyl die hoër temperatuur (700 en 800 °C) bloekom- en 600 °C swartwattel-biochars oesopbrengste met 26-79% onderdruk het, toegeskryf aan fitotoksisiteit, alkaliniteit en vermindering van B en grondwater beskikbaarheid. Daar is gevind dat alle vars biochars totale beskikbare water verminder as gevolg van hoë mikroporositeit. Terwyl in die verouderde biochar-proef slegs lae- temperatuur bloekom biochar (500 °C) die totale beskikbare water onderdruk het. Biochar- veroudering het grond totale N verminder, maar effens verhoogde effektiewe katioonuitruilvermoë en maklik beskikbare waterinhoud, maar nie in vergelyking met die verouderde sandbeheer nie. Die veroudering van bloekom- en swartwattel-biochar het ook die fitotoksisiteit wat in sekere vars biochars voorkom, verminder. Nie een van die verouderde biochars het egter 'n betekenisvolle effek op blomkoolopbrengste in vergelyking met die kontrolesand gehad nie. Die resultate van hierdie studie beklemtoon die belangrikheid van biochar-eienskappe, soos beïnvloed deur pirolise toestande en grondstof, op gewasgroeireaksie.af_ZA
dc.description.versionMastersen_ZA
dc.format.extent83 pages : illustrations (some color)en_ZA
dc.identifier.urihttps://scholar.sun.ac.za/handle/10019.1/130641
dc.language.isoen_ZAen_ZA
dc.language.isoen_ZAen_ZA
dc.publisherStellenbosch : Stellenbosch Universityen_ZA
dc.rights.holderStellenbosch Universityen_ZA
dc.subject.lcshInvasive alien plants -- South Africaen_ZA
dc.subject.lcshBiocharen_ZA
dc.subject.lcshSoils -- Qualityen_ZA
dc.subject.lcshSoils, Effect of temperature onen_ZA
dc.subject.lcshSoil fertilityen_ZA
dc.subject.lcshCrop production scienceen_ZA
dc.subject.nameUCTDen_ZA
dc.titleThe effect of invasive alien plants (IAPs) biochar properties on soil quality and crop productionen_ZA
dc.typeThesisen_ZA
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