Extent of Soil Acidity in No-Tillage Systems in the Western Cape Province of South Africa
Adriaan Liebenberg | John Richard (Ruan) van der Nest | Ailsa G. Hardie | Johan Labuschagne | Pieter Andreas Swanepoel
Roughly 90% of farmers in the Western Cape Province of South Africa have converted to no-tillage systems to improve the efficiency of crop production. Implementation of no-tillage restricts the mixing of soil amendments, such as limestone, into soil. Stratification of nutrients and pH is expected. A soil survey was conducted to determine the extent and geographical spread of acid soils and pH stratification throughout the Western Cape. Soil samples (<i>n</i> = 653) were taken at three depths (0–5, 5–15, 15–30 cm) from no-tillage fields. Differential responses (<i>p</i> ≤ 0.05) between the two regions (Swartland and southern Cape), as well as soil depth, and annual rainfall influenced (<i>p</i> ≤ 0.05) exchangeable acidity, Ca and Mg, pH<sub>(KCl)</sub>, and acid saturation. A large portion (19.3%) of soils (specifically in the Swartland region) had at least one depth increment with pH<sub>(KCl)</sub> ≤ 5.0, which is suboptimal for wheat (<i>Triticum aestivum</i>), barley (<i>Hordeum vulgare</i>), and canola (<i>Brassica napus</i>). Acid saturation in the 5–15 cm depth increment in the Swartland was above the 8% threshold for production of most crops. Acid soils are a significant threat to crop production in the region and needs tactical agronomic intervention (e.g. strategic tillage) to ensure sustainability.
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