Effects of Potassium Chloride and Potassium Sulfate on Sucrose Concentration in Sugarcane Juice Under Pot Conditions

Abstract

Sugarcane is generally fertilized with potassium chloride (KCl). It was reported in Okinawa, Japan, that potassium (K) in sugarcane juice has a negative effect on juice sucrose concentration. However, in some experiments, increasing K levels with potassium sulfate (K₂SO₄) did not reduce sucrose concentration. We hypothesized that sugarcane quality is affected not only by K but also by other components of K fertilizers, such as Cl⁻ and SO₄ ²⁻. To test this hypothesis, two pot experiments were performed using different K levels supplied by KCl and K₂SO₄. Juice K⁺ and Cl⁻ concentrations markedly increased with K levels irrespective of K type; however, there was little effect of the treatments on SO₄ ²⁻ concentration. In the first experiment, as K levels increased, both KCl and K₂SO₄ application tended to increase sucrose concentration in August samples. In later periods, however, the relationships completely changed based on the K type: sucrose concentration tended to be reduced by KCl application but increased by K₂SO₄ application. Similar results were obtained in the second experiment, which resulted in lower sucrose concentration with higher levels of KCl; however, there was no negative effect of K₂SO₄ treatment. These results suggest that Cl⁻ is the primary factor in sucrose reduction. K⁺ concentration strongly affected Cl⁻ concentration in all K types; however, the rate of increase was lower when only K₂SO₄ was provided, thereby indicating that it is possible to lower Cl⁻ concentration by K₂SO₄ application. This measure could lead to quality improvement.