Abstract
Although potassium nutrition stands out in increasing plant tolerance to salinity, not much is known on the optimum potassium (K) rates of potato (Solanum tuberosum L.) grown under salt stress. Two lysimeter experiments were conducted in two seasons to study the effects of four levels of K fertilization (0, 200, 400, and 600 kg K ha
−1
) on the yield of four potato cultivars (Spunta, King Edward, Alpha, and Diamont) grown under salt stress. Saline treatment was imposed by irrigating with water that was salinized with sodium chloride (NaCl) salt. The electrical conductivity (EC) of the irrigation water was 9.38 dS m
−1
. Polynomial quadratic models were developed and used to describe total yield response of the four potato cultivars to optimum rate of potassium application (K
0
) in both seasons. In all cases, total yield response to K fertilizer increased more steeply at lower than at higher rates of K application. The magnitude of response diminished as the K level increased. Diamont cultivar would have optimum yield (Y
opt
) of 18.29 and 14.14 mg ha
−1
if K
0
of 3.27 and 2.49 units ha
−1
were applied in fall 1994 and summer 1995, respectively. Meanwhile, the net returns of Diamont cultivar as a result of receiving optimum rates of K fertilization were the highest whereas, net returns of King Edward cultivar were the least in both seasons.