Strategies to facilitate lime movement in no-tillage crop production systems

Thesis (MScAgric)--Stellenbosch University, 2023.

ENGLISH ABSTRACT: Soil acidity, particularly in the subsurface, threatens the sustainability of no-tillage crop production systems. Two field experiments were conducted to generate a novel perspective on alleviation of soil acidity in no-tillage crop production systems. Experiment 1 was conducted over two years on a sandy loam Oakleaf no-tillage system in the Swartland region of South Africa, receiving an average rainfall of 509 mm yr⁻¹. Initial soil pH(KCl) values were 6.0, 5.3, 4.3 and 4.2 in the 0 – 5, 5 – 10, 10 – 20 and 20 – 30 cm depth increments, respectively. Treatments existed of lime incorporation, surface applied lime forms (i.e., class-A, pelletised and hydrated lime) and combined surface application of lime plus gypsum. Wheat (Triticum aestivum L.) and canola (Brassica napus L.) crop parameters were monitored in year one and two, respectively. Combined surface application of 0.55 Mg ha⁻¹ calcitic lime plus 1.25 Mg ha⁻¹ gypsum decreased (p < 0.05) exchangeable acidity in the 20 – 30 cm depth by 0.30 cmolc kg⁻¹ relative to the control at 12 months. Incorporation of 1.67 Mg ha⁻¹ calcitic lime through once-off strategic tillage with a chisel plough and the combined surface application of 0.55 Mg ha⁻¹ calcitic lime plus 1.25 Mg ha⁻¹ gypsum both raised (p < 0.05) soil pH(KCl) by 0.45 units in the 20 – 30 cm depth relative to the control at 18 months. Surface application of both 1.56 Mg ha⁻¹ hydrated lime and 1.75 Mg ha⁻¹ pelletised lime resulted in an over-liming effect of the 0 – 5 cm depth after 6 months. At 18 months, there were no differences (p > 0.05) in soil pH(KCl) in any depth increment (0 – 30 cm) between hydrated, pelletised or calcitic lime. Lime incorporation through strategic tillage with a chisel plough resulted in the lowest (p < 0.05) wheat plant population in year one. Leaf area index, above-ground biomass, yield and seed quality parameters were not affected (p > 0.05) by the treatments in both years. Experiment 2 was conducted over three years on a clayey loam (Witfontein) no-tillage system in the western Rûens region of South Africa, receiving an average rainfall of 529 mm yr⁻¹. Initial soil pH(KCl) was 5.4, 5.2 and 5.0 in the 0 – 5, 5 – 15 and 15 – 30 cm depths, respectively. Treatments existed of lime incorporation through once-off strategic tillage, surface application of calcitic lime and pelletised lime (surface applied and in-row placement). Barley (Hordeum vulgare L.) crop parameters were monitored in year one and three. At 30 months, incorporation of 2 Mg ha⁻¹ calcitic lime through once-off strategic tillage with a disc, chisel or ripper plough did not increase (p > 0.05) soil pH(KCl) relative to exclusive surface application of 2 Mg ha⁻¹ calcitic lime in none of the depth increments (0 – 5, 5 – 15 or 15 – 30 cm). Pelletised lime treatments, whether surface applied or placed in-row, did not show any superiority to surface applied calcitic lime in alleviating soil acidity. There was no treatment effect (p > 0.05) on barley crop parameters in year one or three.

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Masters