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

Adriaan Liebenberg,Pieter Andreas Swanepoel,Johan Labuschagne,John Richard (Ruan) Van Der Nest,Ailsa G Hardie

doi:10.3390/land9100361

Abstract

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 (n = 653) were taken at three depths (0–5, 5–15, 15–30 cm) from no-tillage fields. Differential responses (p ≤ 0.05) between the two regions (Swartland and southern Cape), as well as soil depth, and annual rainfall influenced (p ≤ 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 (Triticum aestivum), barley (Hordeum vulgare), and canola (Brassica napus). 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.

Highlights

Conservation agriculture (CA) is an effective strategy to improve the efficiency of production of crops [1]
The differential depth effect between the southern Cape and Swartland could possibly be due to the acid saturation component of the effective cation exchange capacity (ECEC) of the Swartland soils being higher than that of the southern Cape soils
The parent material and physical attributes, such as texture, of the soils that differ between the Swartland and southern Cape regions may further account for the differences in pH(KCl) and exchangeable acidity, since ECEC depends highly on the texture of a soil [22]

Summary

Introduction

Conservation agriculture (CA) is an effective strategy to improve the efficiency of production of crops [1]. No-tillage is an important part of CA, along with crop rotation and the maintenance of an organic soil cover. No-tillage entails disturbing less than 25% of the total cropped area or implementing soil disturbances that are less than 25 cm wide [2]. The implications of implementing no-tillage is that soil amendments, such as limestone (lime), cannot be mixed into the soil with tillage actions, as in the case of conventional agriculture. In a study by [7], it was found that it took between two and four years for 1.5 t ha−1 of surface-applied lime to move to a depth of 10 cm in a clay loam soil that received

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Conclusion