See more from this Session: C03 Graduate Student Poster Competition
Monday, November 1, 2010
Long Beach Convention Center, Exhibit Hall BC, Lower Level
Useful benchmarks are those based on understanding of biophysical processes that determine crop productivity in response to environment x management interactions. The challenge is translating these complex processes into decision-support that is useful to farmers and policy-makers. The present study defined a benchmark for maize water productivity (WP) based on the relationship between simulated grain yield and water supply (n = 859). Yields were simulated for irrigated and rainfed conditions in 18 locations in Western Corn-Belt using 20-year weather records and site-specific soil properties and management practices. Three parameters were defined for the WP benchmark: x-intercept (~ soil evaporation), slope (~ water-use efficiency), and asymptote (~ yield-potential). The WP benchmark was validated against observations collected from crops grown under near-optimal conditions in a wide range of environments, water regimes, and irrigation systems (n = 123) and used to identify management practices to improve WP in irrigated commercial fields in central Nebraska (n = 777 fields). The defined WP benchmark had x-intercept, slope, and asymptote equal to 100 mm, 19.3 kg ha-1 mm-1, and 14.4 Mg ha-1. When validated against field data, most of the observations were distributed around the WP benchmark, except for five rainfed crops with severe water deficit during silking-pollen shed window. On-farm WP analysis indicate that farmer’s fields are, on average, 20% below the WP benchmark and a substantial number of fields (55%) had water supplies in excess of water requirements to achieve yield-potential. Major opportunities for increasing on-farm WP include turning surface to sprinkler systems, adoption of conservation tillage in fields under soybean-maize rotation, and better irrigation schemes, which together could reduce district-level water requirements by 32% without yield reduction. The WP benchmark defined in this study can be used in other maize-producing regions after calibration of benchmark parameters to site-specific evaporative demand and yield potential.