Effect of application of molasses on sugarcane growth, yield, and chemical properties in a red–yellow soil on Kitadaito Island

Abstract

To improve sugarcane yield in Kitadaito Island, we investigated the effect of molasses, a sugarcane byproduct, on soil fertility, yield, and economical balance in a field experiment. Experimental plots included the control (no molasses application), 20-Mg (20 Mg ha⁻¹ molasses application), and 50-Mg plots (50 Mg ha⁻¹ molasses application). Sugarcane was cultivated for two cropping periods of spring planting and ratoon planting. Molasses were applied before spring planting. The total yield of sugarcane for the two cropping seasons was 87.2 Mg ha⁻¹ in the control plot, 101.3 Mg ha⁻¹ in the 20-Mg plot, and 111.9 Mg ha⁻¹ in the 50-Mg plot, which significantly increased with the molasses application. Available nitrogen in the soil significantly increased with the amount of molasses applied during spring planting, and the available nitrogen increased the yield. The exchangeable potassium in the soil significantly increased with the molasses application compared with the control throughout the test period. Accumulation of exchangeable potassium in the soil was thought to suppress magnesium uptake through competitive inhibition, but there was no difference in leaf magnesium content at harvest, and there was also no difference in sugar content among the treatments. The estimate of profitability by the molasses application showed an increase of 364,000 yen ha⁻¹ in the 20-Mg plot and 544,000 yen ha⁻¹ in the 50-Mg plot compared with the control plot.