Masters Degrees (Soil Science)

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Browsing Masters Degrees (Soil Science) by Author "Du Plessis, M"

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    The effect of gypsum form and source on soil amelioration
    (Stellenbosch : Stellenbosch University, 2024-03) Du Plessis, M; Hardie-Pieters, Ailsa G.; Swanepoel, Pieter Andreas; Stellenbosch University. Faculty of Agrisciences. Dept. of Soil Science.
    ENGLISH ABSTRACT: Studies evaluating the effectiveness of South African gypsum sources are scarce or outdated, as new products, such as granulated and liquid gypsums, have been introduced. The efficacy of calcium (Ca) nitrate and micro-fine (MF) calcitic limes in comparison to multiple gypsum sources has also never been evaluated. Consequently, the main aim of the study was to characterise and compare the effectiveness of various South African gypsum sources for use in crop production. A controlled laboratory study was performed to compare the effectiveness of mined and by-product gypsums and other Ca sources in terms of soil sodicity remediation and saturated hydraulic conductivity (Ksat) improvement. Twelve mined and by-product gypsums sources, MF calcitic limes and calcium nitrate were surface-applied to a sodic, sandy loam soil to achieve an exchangeable sodium percentage (ESP) of 5%. The soils received 300 mm simulated rainfall. Finer by-product gypsum sources (particularly liquid and flue gas desulphurisation (FGD) gypsums) exhibited faster dissolution rates and superior performance in lowering soil ESP compared to Class A mined gypsums. Only the liquid, phospho-, FGD gypsums and calcium nitrate significantly increased soil hydraulic conductivity compared to the control. The MF calcitic limes had no effect on the sodic soil properties. In a separate controlled laboratory study, 7 gypsum sources (reagent grade gypsum, phosphogypsum, granulated phosphogypsum, mine water, FGD, mined gypsums), two calcitic lime products (granulated MF and agricultural lime), hydrated agricultural lime, and a 1:1 combination of mined agricultural gypsum and calcitic lime were surface-applied to two Western Cape acid (sandy and sandy loam) soils and compared in terms of soil acidity remediation in 50 mm increments to a depth of 400 mm. The soils received 1000 mm simulated rainfall. Gypsum could not substitute lime in terms of acidity neutralisation but did show capability in displacing acidity away from the topsoil. The 1:1 combination of mined Class A gypsum and calcitic lime proved to be a viable substitute for lime alone. In a greenhouse pot trial, 6 gypsum products (FGD gypsum, mine water gypsum, phosphogypsum, granulated phosphogypsum, mined recrystallised gypsum and mined gypsum) were surfaced applied to an acidic, sandy soil (5.1% clay) to raise soil Ca levels to 400 mg kg⁻¹. The objectives of this study were to investigate the effect of different sources and forms of gypsum on the chemical properties of an acid, sandy soil and assess their effects on canola growth and nutrient uptake. Canola (Blazer TT cultivar) plants were grown in the pots and harvested after 7 weeks. Shoot and root biomass, foliar nutrient content soil chemical properties were then determined. In the short- term, granulated phosphogypsum and mined recrystallised gypsum were superior in terms of correcting acidity and improving root growth compared to the other gypsums, but all gypsum sources adequately addressed Canola Ca and S deficiency.