Constraints on Water Use Efficiency of Drought Tolerant Maize Grown in a Semi-Arid Environment.

Identifying the constraints on crop water use efficiency (WUE) will help develop strategies to mitigate these limitations. The objectives of this research were to 1) develop a boundary function for maize using data (n=260) from research projects conducted at Bushland, TX, and 2) compare the yields of two recently developed, drought tolerant maize (Zea mays L.) hybrids with the boundary function and examine possible abiotic and biotic constraints on maximizing water use efficiency.  A commercially available hybrid and an experimental hybrid were grown in 2012 (high environmental stress environment) and 2013 (moderate stress environment) in 48 weighing lysimeters containing soil monoliths of either clay loam, silt loam, sandy loam, or fine sand in a rain shelter facility. Plant density was 8 plants m^-2; irrigation treatments were 50% and 80% replacement of predicted crop evapotranspiration.  Environmental conditions such as high vapor pressure deficits and temperature were the principal constraint on achieving the yield potential of maize.  Differences in breeding resulted in significant differences in WUE, yield and yield components between hybrids in response to environmental conditions during post-silking.  Soil textural class was also a significant constraint on WUE and harvest index (HI), with larger WUE and HI from crops in the fine sand and sandy loam compared with those of the crops in the clay loam and silt loam.  Continued increases in the tolerance of maize to abiotic and biotic stresses will be necessary to maintain maize production in the southern High Plains region as irrigation water resources decline.