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

Liebenberg, Adriaan (2021-03)

Thesis (MScAgric)--Stellenbosch University, 2021.

Thesis

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.

AFRIKAANSE OPSOMMING: Grondsuurheid, en die stratifikasie daarvan, is regdeur die Wes-Kaap Provinsie gevind. Grondsuurheid is veral algemeen in die Swartland, waar 19.3% van gronde in hierdie streek ten minste een grondlaag bevat, in alle gevalle dieper as 5 cm, met pH(KCl) ≤ 5.0. Die gemiddelde suurversadigingspersentasie van die Swartland streek was bo die 8% drempelwaarde vir koringproduksie. Die algemene aanneming van geenbewerking bied uitdagings met die aanspreek van ondergrondse suurheid. Aangesien grondsuurheid ‘n beperkende faktor is vir koring (Triticum aestivum), gars (Hordeum vulgare) en canola (Brassica napus) wat in hierdie streke verbou word, moet grondsuurheid aangespreek word. Dit is dus van kritieke belang dat bekalking met die korrekte kombinasie van kalkmateriaal, metode van kalktoediening en fisiese inkorporasie, of gebrek daarvan, gedoen word. Hierdie veranderlikes is geëvalueer op sanderige leemgrond met pH(KCl) 5.5. Resultate van hierdie veldproef dui daarop dat mikro-fyn verkorrelde kalk en Klas A kalsitiese kalk soortgelyke effekte op grond chemiese eienskappe en gewasreaksie tot gevolg het onder die grond-en klimaatstoestande wat tydens hierdie studie geheers het. Die toediening van ʼn klein hoeveelheid (40 kg ha-1) mikro-fyn verkorrelde kalk binne die ry het ʼn weglaatbare effek op grond chemiese eienskappe gehad en die behandeling waar slegs 40 kg ha-1 van die mikro-fyn verkorrelde kalk toegedien is, was die enigste behandeling, buiten die kontrole, waar die pH(KCl) van die grond afgeneem het deur die verloop van hierdie studie. Vergelyking van monsters wat binne die rye en tussen rye geneem is van die behandelinge waar kalkmateriaal binne rye en breedwerpig toegedien is, het ʼn groter (p ≤ 0.05) verhoging in die kalsiuminhoud getoon van die monsters wat tussen die rye geneem is. Van die veranderlikes wat gewasreaksie gemeet het, het canola behandelingsreaksies (p ≤ 0.05) in blaaroppervlakindeks (BOI), bogrondse biomassa en olie-inhoud getoon. Die BOI van canola het slegs by 90 dae na opkoms (DNO) verskil, waar die behandelinge waar grond versteur was en waar mikro-fyn verkorrelde kalk teen 19% minder as die aanbeveelde toedieningspeil toegedien is, die hoogste BOI getoon het. Waar ʼn skottelploeg gebruik was en waar mikro-fyn verkorrelde kalk slegs in die rye toegedien was, was olie-inhoud die laagste (p ≤ 0.05). Gewasreaksie in slegs sommige veranderlikes kan toegeskryf word aan canola se veerkragtigheid en aan die feit dat die bekalking in dieselfde jaar gedoen is, dus het die bekalkingsmateriaal nie voldoende tyd gehad om volledig te reageer met grondsuurheid nie. In die volgende jaar is koring op dieselfde proefperseel geplant. Dit was gedoen om die behandelingseffekte oor twee jaar te monitor. Koring het behandelingseffekte (p ≤ 0.05) in plantpopulasie en bogrondse biomassa by 150 DNO getoon. Waar ʼn skottelploeg gebruik was, was beide plantpopulasie en bogrondse biomassa die hoogste. Verhogings in grond-pH in die 5 – 15 cm diepte het positief gekorreleer met verhoogde bogrondse biomassa- en proteïeninhoud van koring. Verhoging in die effektiewe katioon-uitruilvermoë het ook gekorreleer met verhoogde bogrondse biomassa van koring. The hoeveelheid reënval, sowel as die reënvalverspreiding, mag bygedra het tot die min verskille tussen behandelings in 2020.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/109894
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