Viability of shortened canola production systems in a winter rainfall region of South Africa based on eleven years of field data

Abstract

Crop rotation is a key component of conservation agriculture, known to enhance yields and break the cycles of pests and diseases. In the Western Cape, South Africa, canola has become an increasingly important cash crop, with producers considering shorter rotation periods to boost profitability. However, concerns remain regarding yield stability, economic returns and disease pressure from particularly Sclerotinia stem rot. The study utilised a regionally significant eleven-year dataset from a long-term field trial (2013–2023) near Riversdale, Western Cape, to assess these concerns. Shortened rotations (one to two years between canola plantings) were compared to conventional longer rotations between canola crops. Results show that shortened rotations delivered competitive yields and significantly higher gross margins (up to 20%), despite higher input costs. Stem rot incidence was highly variable across years (ranging between 0% and 40%) and was primarily driven by rainfall during flowering, with no consistent correlation with rotation length. Overall, the study indicates that with appropriate management, shortened canola rotations are economically viable for producers, offering a profitable alternative amid declining cereal crop margins. Although not measured in this study, preventing future herbicide resistance will require integrated weed and disease management to support long-term sustainability.