Browsing by Author "Mncedi, Sipho"

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    The effect of invasive alien plants (IAPs) biochar properties on soil quality and crop production
    (Stellenbosch : Stellenbosch University, 2024-03) Mncedi, Sipho; Hardie-Pieters, Ailsa G.; Swanepoel, Pieter Andreas; Stellenbosch University. Faculty of Agrisciences. Dept. of Soil Science.
    ENGLISH 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.