Abstract
The growth and nutrient uptake of forage sugarcane plants were examined under multi-ratooning cultivation using various K2O application levels to develop a management system considering the mineral balance in the plant. Compared with the usual management (control), the plant in the plots with reduced K2O application levels had a lower K/(Ca+Mg) ratio (index of mineral balance) and a significant difference was observed from the 2nd ratoon. This was because the K concentration decreased and the Ca and Mg concentrations increased due to reduction of K2O application level. Therefore, the K/(Ca+Mg) ratio can be improved by continuous K2O fertilizer reduction. On the other hand, soil exchangeable K contents were lowered by reduced K2O application and the yield was decreased significantly in multi-ratooning cultivation. Therefore, continuous K2O fertilizer reduction management is not recommended and the usual amount of K2O fertilizer should be maintained. Since the soil exchangeable K contents decreased even in the control plot, additional K2O fertilizer such as manure should be applied in order to maintain the yield level in multi-ratooning crops. The usual amount of N application was considered appropriate and that of P2O5 application superfluous. Since the soil exchangeable Ca and Mg contents were reduced in multi-ratooning crops, Ca and Mg application to the soil should be conducted using lime.
