Liming strategies for barley and canola production under no-tillage.

Van der Nest, John Richard Ruan (2021-03)

Thesis (MScAgric)--Stellenbosch University, 2021.


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.

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