A field study on cotton ( Gossypium hirsutum L., cv.) was carried out from 2005 to 2008 in the Cukurova Region, Eastern Mediterranean, Turkey. Treatments were designated as I100 full irrigation; DI 70, DI 50 and DI 00 which received 70, 50, and 0% of the irrigation water amount applied in the I100 treatment. The irrigation water amount to be applied to the plots was calculated using cumulative pan evaporation that occurred during the irrigation intervals. The effect of water deficit or water stress on crop yield and some plant growth parameters such as yield response, water use efficiencies, dry matter yield (DM), leaf area index (LAI) as well as on lint quality components was evaluated. The average seasonal evapotranspiration ranged from 28715 (DI 00) to 58480 mm ( I100). Deficit irrigation significantly affected crop yield and all yield components considered in this study. The average seed cotton yield varied from 1369197 (DI 00) to 3397508 kg ha -1 ( I100). The average water use efficiency (WUE ET) ranged from 6.01.6 ( I100) to 4.80.9 kg ha -1 mm -1 (DI 00), while average irrigation water use efficiency (WUE I) was between 9.43.0 ( I100) and 14.44.8 kg ha -1 mm -1 (DI 50). Deficit irrigation increased the harvest index (HI) values from 0.260.054 ( I100) to 0.320.052 kg kg -1 (DI 50). Yield response factor (Ky) was determined to be 0.98 based on four-year average. Leaf area index (LAI) and dry matter yields (DM) increased with increasing water use. This study demonstrated that the full irrigated treatment ( I100) should be used for semiarid conditions with no water shortage. However, DI 70 treatment needs to be considered as a viable alternative for the development of reduced irrigation strategies in semiarid regions where irrigation water supplies are limited.
