The effect of nitrogen and potassium fertilizers on growth parameters and carbohydrate contents of sweet sorghum cultivars.

Sweet sorghum is tolerant to high temperature and drought and can be considered as an alternative crop to sugar beet and maize in Iran. In this study, the effects of nitrogen and potassium fertilizers on growth parameters including stem height, stem diameter, stem fresh weight, total fresh weight; carbohydrate contents including total sugar, brix value, sucrose content and purify; and juice extract of two sweet sorghum cultivars were determined. Three rates of N-fertilizer (0, 90, 180 kg urea ha(-1)) and two rates of K fertilizer (0 and 50 kg potassium sulfate ha(-1)) assigned as main plots and two sweet sorghum cultivars (Rio and Keller) as subplots. Growth parameters at soft dough and physiological maturity stages and carbohydrate contents at physiological maturity stage were determined. Results showed that application of 180 kg urea ha(-1) as compared to control at physiological maturity significantly (p < 0.01) increased stem height (12.65%), stem fresh weight (24.57%), total fresh weight (78.22%), total sugar (39.25%), sucrose content (9%) and juice extract (34.96%). Application of 50 kg potassium sulfate ha(-1) increased (p < 0.05) stem fresh weight (24.33%), total fresh weight (25.44%), total sugar (10.50%), and juice extract (9%) at physiological maturity. The highest growth parameters, carbohydrate contents and juice extract were obtained with the application of 180 kg urea ha(-1) and 50 kg potassium sulfate ha(-1) using cultivar (cv) Keller. The best results were taken with the application of both fertilizers.