Interaction of Irrigation, Nitrogen Management, and Crop Genetics on Water Productivity of Maize and Kentucky Bluegrass.

Water scarcity is a major threat to the sustainability of irrigated agriculture and urban landscapes and management practices that maximize the use of a limited water supply are critical. Controlled deficit irrigation is becoming more common and better understanding the genetic x management x environment interactions of these systems is needed. This presentation will summarize research on crop water productivity of controlled deficit irrigation of maize and Kentucky bluegrass and interactions with nitrogen and/or crop genetics. In a five year study in Colorado, fully irrigated maize yield averaged 12.3 Mg ha^-1, with a crop water productivity of 2.0 kg m^-3. Under controlled deficit irrigation, maize yield was lower, 9.9 Mg ha^-1, but crop water productivity was greater, 2.4 kg m^-3. In both maize and Kentucky bluegrass, high N supply reduces root growth, which in turn limits access to soil water.  Similarly, in both crops N supply can be managed to influence growth and water consumption. For maize, drought tolerant hybrids were evaluated with and without water limitations. With adequate water, the drought tolerant hybrids have lower yield than conventional hybrids, but they do have higher water productivity when water is limited.