Soils and seasons effect on sugarcane ratoon yield

Abstract

Sugarcane yields are known to decline with successive ratoon crops, a phenomenon termed ratoon yield decline (RYD), and the rate of decline is largely dependent on the environment in which the crop grows. An environment in sugarcane production is characterized by harvest season and soil type, and gaining an understanding on how these influence RYD, can assist growers manipulate them through best practices to attain longer profitable ratoon cycles. This study aimed to quantify the effect of harvest seasons and soil types on RYD for tons cane per ha per annum (TCHA), sucrose content (SUC%) and tons sucrose per ha per annum (TSHA). To achieve this, 15 year (2000–2014) commercial field data from four large growers of the Eswatini sugarcane industry with similar climatic conditions were analyzed using linear mixed models. Season, soil and season x soil effects had highly significant (p < 0.0001) effect on RYD for TCHA and TSHA. The order of importance for TCHA was season > soil > season x soil while for TSHA it was soil > season > season x soil. SUC% was not significantly (p > 0.05) affected by change in ratoon crop numbers, although there were indications of increase with increase in ratoon number. Early season harvests had the highest rate of cane yield decline (−3.33 TCHA) followed by late season (−2.30 TCHA), and mid season (−1.98 TCHA) had the lowest. Early (−0.33 TSHA) and late (−0.32 TSHA) season harvests had higher rates of sucrose yield decline than mid season harvests (−0.26 TSHA). Poor draining soils had a higher rate of cane yield decline (−2.92 TCHA) than moderate draining (−2.30 TCHA) and good draining (−2.43 TCHA) soils. Similarly, poor draining soils had a higher rate of sucrose yield decline (−0.38 TSHA) than moderate draining (−0.28 TSHA) and good draining (−0.25 TSHA) soils. There were larger variations in rates of yield decline for season x soil effects for TCHA (−1.70 to −3.98) and TSHA (−0.23 to −0.46) than the main effects of seasons and soils indicating the complexity associated with yield traits. The results of this study will inform sugarcane yield forecasting models to estimate yields of plant cane and ratoon crops for each soil class, adjusted for harvest seasons. Plant breeders can segregate environments according to their potential RYD and select genotypes for specific adaptations to optimize genetic gains. Growers on the other hand will be able to identify profitable ratoon numbers for each growing environment and schedule their replant programs accordingly.