Relationships between nutrients and sucrose concentrations in sugarcane juice and use of juice analysis for nutrient diagnosis in Japan

Sugarcane is an important economic crop in southwest Japan, but its production is decreasing. To increase sugar production, both sugarcane yield and quality should be improved. Fertilizer management is one of the factors that influence sugarcane quality. We accordingly focused on nutrients present in sugarcane juice and attempted to identify the key factors affecting sugarcane quality. We collected sugarcane samples from 2013 to 2015 from all of the sugar mills in Japan and examined the relationships between juice nutrients and sucrose concentration. Juice analysis over 3 year showed that potassium (K⁺) and chloride (Cl^?) were the most abundant cation and anion in the juice and that both negatively correlated with the sucrose concentration. K⁺ and Cl^? concentrations significantly varied depending on production areas and those with higher K⁺ and Cl^? concentrations had a low sucrose concentration. This finding suggests that sugarcane in those areas may have been supplied with these two ions in excess. Electrical conductivity (EC) in the juice always positively correlated with K⁺ and Cl^? concentrations. EC may thus be a reliable indicator of K⁺ and Cl^? concentrations and could be used for nutrient diagnosis because of its ease of measurement. For improving sugarcane quality, we recommend that potassium chloride, which supplies both K⁺ and Cl^? and is a commonly used potassium fertilizer for sugarcane production in Japan, should be used in lower quantities in a year following one in which the EC of sugarcane juice at harvest is found to be high.