Effects of variety, environment and management on sugarcane ratoon yield decline

Factors influencing ratoon yield decline (RYD) are often unclear and difficult to unravel. The objectives of this study were (i) to explore the relative contributions of variety, environment and management to RYD, and (ii) to evaluate a method of detecting statistical differences in RYD between treatments. Four sets of trials, comprising six irrigated variety trials from South Africa and Swaziland (set 1), four variety trials from the rainfed KwaZulu-Natal region (set 2), three cycles of a long-term burning and trashing trial (set 3), and two variety x nematicide trials (set 4) were analysed. Yield data were collected over six or more crops. Cane yield was fitted as a linear or quadratic function of ratoon number for each replicate of each trial. The differences between the treatment linear or quadratic coefficients were analysed using ANOVA. Significant (p < 0.05) and highly significant (p < 0.001) differences in quadratic coefficients were observed between varieties in two out of six trials in set 1. No significant differences between variety coefficients were observed in trials in set 2. Highly significant differences were observed between the burning and trashing treatments in set 3. In set 4, a significant difference in the linear coefficient was observed between variety x nematicide treatments in one trial only. The RYD patterns generally varied between trials, while variability of treatments/varieties within trials was negligible. Hence, it was apparent that environment may have an overriding effect on RYD, followed by the effects of management and variety, respectively. The statistical method illustrated here may be applied to other studies of RYD.