Department of Agronomy

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Browsing Department of Agronomy by browse.metadata.advisor "Hardie-Pieters, Ailsa G."

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    Crop response in the Western Cape of South Africa to liming soil under no-tillage and following once-off tillage in a no-tillage regime
    (Stellenbosch : Stellenbosch University, 2021-03) Liebenberg, Adriaan; Swanepoel, Pieter Andreas; Hardie-Pieters, Ailsa G.; Labuschagne, Johan; Stellenbosch University. Faculty of AgriSciences. Dept. of Agronomy.
    ENGLISH ABSTRACT: Soil acidity, and the stratification thereof, was found throughout the Western Cape Province. Soil acidity is especially prevalent in the Swartland, where 19.3% of soils in this region have been found to contain at least one soil layer, in all cases deeper than 5 cm, with pH(KCl) ≤ 5.0. The mean acid saturation percentage of the Swartland region was above the 8% threshold for wheat production. The wide adoption of no-tillage has presented challenges to address subsoil acidity. Since soil acidity is a limiting factor for wheat (Triticum aestivum), barley (Hordeum vulgare) and canola (Brassica napus) grown in these regions, acidity should not remain unaddressed. Therefore, it is crucial that liming is done with the correct combination of liming material, method of application and physical incorporation, or lack thereof. These variables were evaluated on sandy loam soil with pH(KCl) 5.5. Results from this field trial indicate that micro-fine lime pellets and Class A calcitic lime yield similar results on soil chemical properties and crop response under the soil and climatic conditions that prevailed during this study. The in-row application of a small amount (40 kg ha-1) of micro-fine lime pellets had a negligible effect on soil chemical properties and the treatment where only 40 kg ha-1 of micro-fine lime pellets were applied was the only treatment, along with the control, where soil pH(KCl) decreased over the course of this trial. Comparison between samples taken in-row and between crop rows in the treatments where liming material was applied in-row and broadcast, showed a greater (p ≤ 0.05) increase in Ca content in the samples taken between crop rows than in-row. Of the crop response variables measured, canola showed treatment responses (p ≤ 0.05) in leaf area index (LAI), aboveground biomass and oil content. Canola LAI’s only differed at 90 days after emergence (DAE), with the treatments where soil was disturbed and where micro-fine lime pellets were applied at 19% below the recommended rate having the highest LAI’s. Where a disc plough was used and where micro-fine lime pellets were applied in-row only, oil contents were the lowest (p ≤ 0.05). The crop responses in only some variables can be ascribed to the resilience of canola and the fact that lime application was done in the same year, thus the liming materials did not have sufficient time to react with soil acidity. In the following year, wheat was planted on the same site. This was done to monitor treatment effects over two years. Wheat showed treatment responses (p ≤ 0.05) in plant population and aboveground biomass at 150 DAE. Where a disc plough was used, both the plant population and aboveground biomass was the highest. Increases in soil pH in the 5 – 15 cm soil depth layer positively correlated with increased aboveground biomass and wheat grain protein content. Increasing effective cation exchange capacity also correlated with increased aboveground biomass in wheat. The amount of rainfall, as well as rainfall distribution, may have contributed to the few treatment differences in 2020.
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    Liming strategies for barley and canola production under no-tillage.
    (Stellenbosch : Stellenbosch University, 2021-03) Van der Nest, John Richard Ruan; Swanepoel, Pieter Andreas; Labuschagne, Johan; Hardie-Pieters, Ailsa G.; Stellenbosch University. Faculty of AgriSciences. Dept. of Agronomy.
    ENGLISH ABSTRACT: The slow movement of lime in soil combined with no-tillage practices that restricts the incorporation of surface broadcast lime deeper into the soil has led to an increase in soil acid stratification with depth in soils under no-tillage over the long-term in the Western Cape Province of South Africa. A soil survey was conducted across the southern Cape and Swartland regions of the Western Cape Province to determine the extent and geographical spread of soil acidity and stratification (Objective 1). Soil samples were taken on long-term no-tillage fields at depth increments of 0 – 5, 5 – 15 and 15 – 30 cm. It was found that 19.3% of the soils surveyed in the Swartland had at least one depth increment with a pHKCl lower than 5.0, which is, in general, below optimal for crop production. A field trial was also established in 2019 (Year 1) to investigate the effect of form, fineness and purity of lime as well as different degrees of incorporating lime into the soil, on soil chemical attributes (Objective 2) as well as on the growth and development of barley (Year 1) and canola (Year 2) (Objective 3). The field trial consisted of ten treatments which included a control treatment, 95% calcium carbonate equivalent (CCE) surface broadcast calcitic lime, 88% CCE surface broadcast lime, lime incorporated with either a disc plough, a chisel plough or a ripper, pelletised lime placed in-row (40 kg ha-1), pelletised lime placed in-row and broadcast at 960 kg ha-1, pelletised lime placed in-row and broadcast at 770 kg ha-1 and pelletised lime broadcast at 1000 kg ha-1. Minor differences in lime purity, type of tillage action (disc plough, chisel plough and ripper) used when incorporating lime as well as form and fineness of lime (pelletised micro-fine) led to an increase (p ≤ 0.05) in pHKCl up to a 30 cm depth, but did not show major crop responses within the first or second growing season after receiving 810 - 1000 kg ha-1 of lime on a sandy loam soil (pHKCL of 5.05; SD ± 0.33 at 0 – 30 cm) that received a total of 558 mm of rainfall. Broadcasting pelletised micro-fine lime at the recommended rate however, led to the greatest (0 - 5 cm depth) as well as the quickest increase in pHKCl, up to a 30 cm depth three months after liming. Applying less than the recommended rate led to more effective neutralisation of soil acidity. Micro-fine pelletised lime however, did not lead to a greater crop growth and productivity within two growing seasons following liming compared to conventional class A lime. There was however a trend for a one-off strategic tillage to result in greater crop biomass production. The positive response of crop growth to a one-off strategic tillage was most likely attributed to deeper redistribution of lime in the soil (15 – 30 cm depth), an increase in nutrient mineralisation and decrease in nutrient stratification, alleviation of soil physical limitations and reduced weed pressure.