Masters Degrees (Soil Science)

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Browsing Masters Degrees (Soil Science) by Author "Du Toit, Dawid Jacob Johannes"

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    Effect of lime source, form and placement on soil pH neutralisation and permeation
    (Stellenbosch : Stellenbosch University, 2021-03) Du Toit, Dawid Jacob Johannes; Hardie-Pieters, Ailsa G.; Swanepoel, Pieter Andreas; Stellenbosch University. Faculty of AgriSciences. Dept. of Soil Science.
    ENGLISH ABSTRACT: Currently, agricultural producers in South Africa are uncertain about the relative effectiveness of locally available class A and granulated micro-fine lime sources, especially in terms of soil permeation and correction of subsoil acidity. There is also limited information regarding the effect of lime placement (surface, band-placement and incorporation) on subsoil acidity alleviation and crop growth. Therefore, the main aim of the study was to compare the effectiveness of various local lime sources (calcitic and dolomitic) and forms (class A, micro-fine and granulated micro-fine) at increasing soil pH and permeating through different textured soils. A laboratory soil-lime incubation study was conducted to compare the acid neutralisation capacity of various local dolomitic and calcitic lime sources (i.e., different quarries) and forms (class A, micro-fine and granulated micro-fine lime) at increasing soil pH over time under controlled conditions in three acid soils (sand, sandy loam, and loam). All liming materials were applied (adjusted for CCE) to reach a target pHKCl of 5.5 on the three soils, incubated at around 85% field capacity and room temperature, and then pH measured at intervals of 1, 4, 7, 14, 21, 30, 47, 60, 90, 180, 275 and 365 days. Ungranulated micro-fine limes were found to have a higher rate of dissolution than class A lime, but the difference in pH obtained attenuated over time. The granulated micro-fine lime was found to be the least effective in correcting soil acidity due to largely remaining intact. The difference in performance between commercially available class A limes was of little importance, if applied based on CCE. Chemical purity (Ca%, CCE) was found to be the main factor effecting the reaction of a liming material in soil and particle fineness only determines the short-term reaction (4-7 days) of the limes. A winter rainfall laboratory column study was carried out on two soils (sand and loam) to compare the soil permeation of different calcitic lime forms (class A, micro-fine and granulated micro-fine). Lime was surface applied to soil columns (40 cm) and irrigated in six events with a total of 350 mm water over 12 weeks. The soil chemical effects of all the surface applied limes were limited to the top 5 cm only. Lastly, a greenhouse barley (Hordeum vulgare) pot trial was conducted to assess short-term crop response to lime form and placement. Lime (class A, micro-fine and granulated micro-fine) was applied (surface, band-placed or incorporated) to an acid loamy sand soil before barley planting. The effects of liming materials on soil chemical attributes were confined to its point of placement. Thorough incorporation of lime more effectively neutralised soil acidity below 5 cm, especially Mn toxicity, resulting in larger barley shoot biomass after six weeks. The granulated lime was once again the least effective due to partial dissolution. The results of this study highlight that, if class A limes are corrected for CCE, the difference between the respective class A lime sources and micro-fine limes attenuates over time and the effects of surface applied lime is confined to its point of placement.