Effects of Different Kinds of Potassium and Chloride Salts on Sugarcane Quality and Photosynthesis

Appropriate fertilizer management practices are important to improve sugarcane quality. We have ever reported that KCl and K2SO4 had different effects on sugarcane quality and that only excessive KCl application decreased sucrose concentration in juice, indicating that Cl− is the key factor for the quality improvement. In this study, to see the individual effects of Cl− independent of K+, we established treatments using different kinds of K+ and Cl− salts (50 mM KCl, 25 mM K2SO4, mixture of 12.5 mM MgCl2 and 12.5 mM CaCl2, and 50 mM NaCl). The treatments did not greatly affect quantitative parameters. Plants treated with KCl and K2SO4 had significantly higher juice K+ concentrations. On the other hand, Cl− concentration was remarkably high only in the KCl treatment and the other Cl− salt treatments hardly enhanced Cl− accumulation, suggesting that Cl− needs K+ to be efficiently absorbed. Juice sucrose concentration was lowest in the KCl treatment, and the other treatments had no adverse effects. We observed neither declines of stomatal conductance nor F v/F m; however, the KCl treatment showed a slightly lower CO2 assimilation rate, which may have accounted for the sucrose reduction. From this study, we could not evaluate the single effects of Cl− but revealed that Cl− could have a negative impact on sugarcane quality only when K+ is supplied above sufficiency levels, so that we need to reduce K+ as well as Cl− concentrations to improve sugarcane quality.