Relationships between water balance and the growth and yield of ratoon sugarcane on Minamidaito island

Abstract

The sugarcane yield on Minamidaito Island is relatively low and unstable as it is highly dependent on climatic factors, particularly rainfall. In the present study, we calculated the water balance of ratoon-cane field on the island based on the meteorological data over the past 30 years and analyzed its relationships with sugarcane growth and yield. Water shortage was serious from July to September, with the insufficient water amount accounting for as much as 46% of that for a whole year, because the water consumption by sugarcane greatly exceeded the effective rainfall due to the low precipitation after rainy season. The insufficient water amount during the three months negatively correlated with stem elongation and cane yield, indicating that sugarcane growth and yield are significantly inhibited when exposed to drought at this stage. This trend was further clearer excluding typhoon years in which the maximum wind speed exceeded 25 m s-1. By using the regression equations in the non-typhoon years, it was found that each 100 mm increment in the insufficient water amount from July to September reduced stem elongation by 25.1 cm and cane yield by 14.1 t ha-1, respectively. The present study revealed that the water balance from July to September most strongly affects sugarcane growth and yield and that irrigation during this period is necessary to achieve high yields and stable production on this island.