Water Capture in Single Cross Maize Hybrids Released Between 1963 and 2008.

Maize (Zea mays L.) breeders have successfully improved grain yield for the conditions of the US corn-belt over the past 80 years. Long-term improvement for grain yield under water-limited conditions has also been reported. Grain yield under water limited conditions depends on water use, water use efficiency and harvest index. It has been hypothesized that long-term genetic gain for yield could be due, in part, to increased water capture from the soil. We tested that hypothesis using a set of elite single-cross hybrids that were released by DuPont-Pioneer between 1963 and 2008. 18 and 15 hybrids were grown in the field during 2010 and/or 2011 respectively in Woodland, CA. Crops predominantly grew on stored soil water and drought stress increased as the season progressed. TDR technology was used to measure soil water content down to 300 cm depth through the growing season and seasonal water use was calculated from the change in soil water, adjusted for any water applied by irrigation. Statistical analysis indicated that grain yield increased significantly with year-of-release, but no such trend was observed for total water extraction. Hence, the measured genetic gain for yield for the period represented by this set of hybrids must be related to either increased efficiency of water use or increased carbon partitioning to the grain, rather than increased soil water extraction.