The purpose of this study was to determine the effect of irrigation amount applied with drip irrigation on field maize (Zea mays L.) evapotranspiration (ET), yield, water use efficiency, yield response factor (ky) and net return in a sub–humid environment of Turkey. Irrigation management treatments were created as 125%, 100%, 75%, 50%, 25% and 0% replenishment of water depleted in the 90 cm root zone from 100% replenishment treatment in every seven days. Irrigation amounts ranged from 76 to 1120 mm in 2007 and from 91 to 997 mm in 2008. The treatments resulted in seasonal ET of 311–1078 mm and 298–1061 mm in 2007 and 2008, respectively. The average grain yields varied from 5570 to 16535 kg ha–1. In both seasons, irrigation significantly affected yields, which increased with irrigation up to a level (1100 mm of irrigation water amount), but additional amounts of irrigation did not increase it any further. Yields increased linearly with seasonal ET. The yield response factor (ky) averaged 0.89 over the two seasons. Maximum water use efficiency (WUE) and irrigation water use efficiency (IWUE) values were obtained for the treatment of 25% deficit irrigation. A further increase in water amount from reference irrigation (T–100) increased grain yield but reduced both the WUE and IWUE. The reference irrigation treatment gave the highest net return of $3212 ha–1. The results revealed that the full irrigation is the best choice for higher yield and net income. The results also suggest that 25% deficit irrigation approach may be a good strategy for increase water use efficiencies when full irrigation is not possible.