Tomato is one of the most important vegetables that is widely consumed by humans. High price of tomato due to its outseason production in Bushehr province has made farmers of this area to cultivate it in fall as well as in winter. Proper utilization of water resources, to increase water use efficiency, is deeply sensed wspecially after recent droughts in the south of Iran. Therefore, a study was conducted in Bushehr Agricultural Research Center (Borazjan) to determine the effect of potassium on W.U.E in tomato. This experiment was carried out on the basis of a Randomized Complete Block design (split plot) with three replications during 1999 — 200 1. The treatments were as follows: Irrigation water depth in four levels (50- 70- 90 and 110 mm of pan evaporation) as main plot and potassium sulfate fertilizer in four levels (0- 175- 265 and 350 kg/ha) as sub plot. Results indicated that tomato yield was significantly affected by both factors, however their interactions were not significant. The highest tomato yield (37.84 ton/ha) was obtained through utilization of 175 kg/ha of potassium sulfate along with 50 mm of irrigation water. More quantities of potassium sulfate (>175 kg/ha) did not only decrease water stress effects but even, yield reduction was also observed.The highest W.U.E was 5.1 kg tomato per cubic meter of applied irrigation water.
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