This study was conducted during the 2018/2019 and 2019/2020 seasons in a private orchard located at Sohag governorate. To investigate the impact of soil potassium fertilization at 40, 60 and 80 % from recommended rates and foliar spray with Nano-Chitosan-K at 500, 1000 and 1500 ppm, potassium chelate at 0.5, 1 and 1.5 % and potassium Sulphate at (0.5, 1 and 1.5 %) on growth, yield and fruit quality of William banana. Results showed that treatments with soil potassium fertilization plus foliar spray with Nano-Chitosan-K or potassium chelate significantly increased vegetative growth, nutritional status, yield and fruit quality in William banana than other treatments. Application of soil potassium fertilization combined with foliar application of potassium was preferable to using soil potassium to improve yield. Application of soil potassium fertilization combined with foliar application with Nano-Chitosan-K was more effective than potassium chelate and potassium sulfate. The best results for fruit chemical qualities were measured using 60% mineral k plus 1000 ppm Nano-Chitosan-K.