Studies on the effect of K fertilizers application in increasing water use efficiency (WUE) and decreasing the negative effect of water stress, are quite limited, especially under field conditions. A field experiment was conducted in silty clay loam in the Agricultural Research Station of Abu-Graib-Baghdad, Iraq to study the effect of different levels of K fertilizers application on potato (Solanum tuberosum L.( and their role in decreasing negative effect of water stress.Treatments include four levels of K fertilizer (0, 200, 400 and 600 kg K 2 SO 4 ha -1 ) and two levels of irrigation (after depletion of 50 and 75 % of available water). Results revealed the following:-* Prof. Soil Sci. Dept. -Coll. of Agric. -Univ. of Baghdad -Iraq. ** Assoc. Prof. Soil Sci. Dept. -Coll. of Agric. -Univ. of Baghdad -Iraq.