Furthermore, water productivity, which is the yield or net income per unit of water used in evapotranspiration (Kijne et al. 2003), is expected to increase under deficit irrigation relative to its value under full irrigation, as revealed experimentally for many crops (Tüzel et al. 1994a, b; Zwart & Bastiaanssen 2004; Fan et al. 2005; Fereres & Soriano 2007).