Extent of Soil Acidity in No-Tillage Systems in the Western Cape Province of South Africa

• Main Authors: Adriaan Liebenberg, John Richard (Ruan) van der Nest, Ailsa G. Hardie, Johan Labuschagne, Pieter Andreas Swanepoel
• Format: Article
• Language: English
• Published: MDPI AG 2020-09-01
• Series: Land
• Subjects: acid saturation; exchangeable acidity; calcium; magnesium; dolomitic lime; calcitic lime
• Online Access: https://www.mdpi.com/2073-445X/9/10/361

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_(KCl), and acid saturation. A large portion (19.3%) of soils (specifically in the Swartland region) had at least one depth increment with pH_(KCl) ≤ 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.