This study was designed to evaluate the yield response of low-energy precision application (LEPA) and trickle-irrigated cotton grown on a clay-textured soil under the and Southeast Anatolia Project (GAP) area conditions during the 1999 growing season at Koruklu. in Turkey. The effects of four different irrigation levels (100, 75, 50, and 25% of cumulative Class-A pan evaporation on a 6-day basis) for LEPA, and two irrigation intervals (3-day and 6-day) and three different levels (100, 67, and 33% of cumulative Class-A pan evaporation on a 3-day and 6-day basis) for the trickle system on yield were investigated. Water was applied to alternate furrows through the double-ended Fangmeier drag-socks in the LEPA system. Trickle irrigation laterals were laid out on the soil surface at a spacing of 1.40 m. A total of 814 mm of water was applied to the full-irrigation treatments (100%) for both irrigation systems. Seasonal water use ranged from 383 to 854 ram in LEPA treatments; and 456 to 868 mm in trickle treatments. Highest average cotton yield of 5850 kg/ha was obtained from the fall-irrigation treatment (100%) in trickle-irrigated plots with 6-day intervals. The highest yield in LEPA plots was obtained in LEPA-100% treatment with an average value of 4750 kg/ha. Seed cotton yields varied from 2660 to 5040 kg/ha and 2310 to 5850 kg/ha in trickle irrigation plots with 3-day and 6-day intervals, respectively, and from 2590 to 4750 kg/ha in LEPA plots. Irrigation levels both in LEPA and trickle-irrigated plots significantly increased yield. However, there was no significant yield difference between 100 and 67% irrigation levels in trickle-irrigated plots. Maximum irrigation water use efficiency (IWUE) and water use efficiency (WUE) were found as 0.813 and 0.741 kg/m(3) in trickle-irrigated treatment of 67% with 6-day interval. Both IWUE and WUE values varied with irrigation quantity and frequency. The research results revealed that both the trickle and LEPA irrigation systems could be used successfully for irrigating cotton crop under the and climatic conditions of the GAP area in Turkey. (C) 2002 Elsevier Science B.V. All rights reserved.