Managing Wheat Cultivars to Enhance Water Productivity in Semi-Arid Cropping Systems.

The water productivity of winter wheat is a critical component of semi-arid dryland cropping systems in the U.S. Central High Plains. This presentation aims to identify opportunities to enhance wheat water productivity through cultivar selection and management in this water-limited region. Crop water productivity was quantified by the ratio of grain or above-ground biomass (AGB) productivity to seasonal water use (field method) as well as ¹³C isotope discrimination (CID, analytic method). Long-term crop sequence studies demonstrate that management to increase cropping intensity (e.g., by replacing an 11-month fallow period with a spring oilseed crop) reduced water available to a subsequent winter wheat crop, reduced AGB growth response to an increment of water use, and reduced the fraction of AGB converted to grain. Tillage and N management also altered crop water use and subsequent productivity. CID, an indicator of molecular-level transpiration efficiency, was positively related to crop water productivity of wheat (biomass or grain basis) and also to crop productivity. Commercial and experimental winter wheat varieties differed in CID, which was positively related to variation in grain productivity. However, the quantitative relationship between CID and yield was inconsistent among sites and years. Path analysis was used to quantify multiple linear relationships among linked sets of equations related to yield formation for cultivars observed in multiple environments. Path analysis indicated positive relationships between CID, AGB productivity and other yield components but little direct relationship of CID and yield; variation among components of yield were consistent with compensatory growth processes. These techniques provide opportunity to guide management—including cultivar selection--to achieve yield potential inherent in diverse water-limited growing environments.