A yield gap analysis to assess vulnerability of commercial sugarcane to climatic extremes in southern Africa

Abstract

Sugarcane yields have steadily declined across southern Africa for the past 25 years and, despite research into the causes, there has been limited progress in addressing these trends. This study developed a methodology of assessing yield declines and performed a yield gap analysis to assess and develop recommendations to assist in combating yield declines and offering potential safeguards for the sugarcane industry against climatic extremes. Mill areas from South Africa, eSwatini, Malawi and Tanzania were selected, providing a diversity of regional hydroclimatic conditions and sugarcane agronomic management approaches. Using the AquaCrop crop model, maximum potential yields and yield gaps were simulated based on observed climate and yield data spanning 25 years. Results show that yields are declining for the mill areas in South Africa, Malawi and Tanzania, resulting in increased yield gaps, whilst yields are stagnant in eSwatini resulting in relatively fixed yield gaps. Yield gaps remained high across all six mill areas, suggesting that they remain vulnerable and exposed to climatic extremes. Modelling results suggest that these yield trends, including yield gaps, are primarily attributed to existing crop management approaches as opposed to the climatic regimes in these areas. Recommendations include several solutions that could result in an immediate response and reduce yield gaps while increasing harvestable yields. Such measures include increasing technology transfer and agronomic management education to small-scale outgrowers, adopting drought-resistant, high-yielding sugarcane varieties, contouring and mulching, improving soil structural properties and minimizing in-field traffic. The study concludes that if sugarcane growers are to withstand the effects of extreme climatic events, they have to consider shifting crop management approaches and be proactively included in related research.