Functional diversification and performance of wheat–canola rotations in the Western Cape

Abstract

Crop rotation serves as a fundamental pillar within conservation agriculture (CA) farming systems, enabling the integration of more diverse crops and livestock. With increasing weather variability, new methods are needed to assess the long-term effects of diversification on the agronomic performance of wheat–canola rotations. Therefore, a 17-season Western Cape rotation platform (Mediterranean-type rainfall; eight systems (A–H), livestock integrated leys), and evaluates small grain performance as means, year-to-year stability (CV%) and grain quality. The long-term data were compared using the Functional Diversification Index (FDI), which summarises sequence richness/evenness, cereal–oilseed–legume contrast, cover/ley phases, planter/tillage choice and livestock intensity. This first long-term Western Cape study using an FDI index validated over 17 seasons shows that the most diverse system, wheat–saltbush–medic/clover mix (System H), had the highest relative mean yield stability (∼ 16.90%), while wheat monoculture under reduced tillage had the lowest (∼ 41.16%). The highest wheat protein content is strongly associated with livestock integrated systems (E–H). These findings highlight the interrelationship between diversification practices and agronomic performance in CA systems in the Swartland region. Under Mediterranean-type rainfall, when mean yields are similar, farmers should prioritise rotations with the lowest yield CV% to reduce year-to-year risk while maintaining grain quality.