Yield and tuber quality of potassium treated potato under optimum irrigation conditions

Field experiments were conducted in 1999 and 2001 at Tal Amara Research Station in the Bekaa Valley of Lebanon to determine the response of yield and tuber quality of four potato cultivars ('Spunta', 'Derby', 'Shepody' and 'Umatilla') to added potassium rates: KO (0 potassium), K1 (96 kg K ha(-1)) K2 (192 kg K ha(-1)) and K3 (288 kg K ha(-1)) in absence of water and nitrogen limitations. Data from this study showed that responsive K treatments were evident in both years. However, contrasted responses to applied K were observed among the four cultivars examined. The significant increases of tuber yield in response to K rates that were observed in 1999 for 'Spunta' and 'Derby' were associated with a lowering, for the former, and an increase, for the latter, in tuber dry matter. Similar increases in tuber yield were obtained in 2001 in the potassium treatments for 'Shepody' and 'Umatilla'. However, while for 'Shepody' tuber yield increase was associated with an increase in dry matter content, no increase in this parameter was obtained with 'Umatilla'. For all cultivars, potassium fertilization significantly increased (P < 0.01) the yield of medium (25-75 g) and large size tubers (> 75 g) at the cost of small size tubers (< 25 g). Finally, results showed no significant differences between the two potassium levels K2 and K3 either for tuber yield or dry matter content.