Water use efficiency for grain yield in an old and two more recent maize hybrids

Increasing water use efficiency for grain production, WUEg (i.e. the quotient between grain yield and seasonal evapotranspiration, ET) is of relevance in rainfed crops. A greater WUEg is expected in more recent than in old maize (Zea mays L.) hybrids, based on different reports indicating higher grain yield, higher stress tolerance or similar seasonal ET in more recent than in old maize hybrids. However, there are no reports quantifying WUEg in maize hybrids released in different decades. In this study we quantify WUEg and its components (i.e. grain yield and seasonal ET) and we examine physiological traits during the critical period for kernel set (i.e. plant growth rate, PGRcp; ear growth rate, EGRcp; ET, ETcp and stomatal conductance), in an old and in two more recent maize hybrids grown under contrasting soil water availability. Three maize hybrids, DK2F10 (old hybrid released in 1980) and DK682RR and DK690MG (more recent hybrids, released in 2004), were grown in 5 experiments during 4 seasons; and irrigation and rainfed treatments were used to promote contrasting soil water availabilities. Soil water content was measured every 7-10 days with a neutron probe. Maximum WUEg tended to be higher for more recent (25.1 kg ha(-1) mm(-1)) than for the older hybrid (23.1 kg ha(-1) mm(-1)); and advantages of WUEg were larger and significantly higher in the more recent than in the older hybrid, at lower water availability. The greater WUEg of more recent hybrids was associated with greater grain yield at all water supplies; which was the result of a greater KNP. At low water availability, the greater KNP in more recent hybrids was related to greater PGRcp, ETcp and stomatal conductance than in the old maize hybrid.