Improving Crop Water Productivity In Dryland and Limited Irritation Cropping Systems In The West Central Great Plains.

Drought and water scarcity affect crop productivity in both dryland and irrigated systems in the West Central Great Plains region of the United States, where precipitation ranges from 300 to 450 mm annually. Typical dryland crop production is a two-year rotation of wheat and summer fallow.  Results of a long-term no-till study document greater precipitation storage and use efficiency when the wheat fallow rotation is intensified and diversified. For example, a no-till rotation of winter wheat-maize-summer fallow increased total annualized grain yield by 75% compared to winter wheat – summer fallow.  The higher crop water productivity reduced soil erosion and improved soil physical properties.  The primary challenge with reducing fallow frequency is an increase in yield variability and risk of crop failure. On-going efforts are evaluating whether annual forage crops in the dryland crop rotations can reduce yield variability and improve adaptation to drought. Water scarcity is also driving adaptation of irrigated cropping systems in the Central Great Plains to maximize use of limited water supplies.  Limited irrigation studies have evaluated effects of irrigation timing on annual grain crops, partial season irrigation of forages, and crop rotations with both irrigated and dryland crops.  Compared to a continuous corn system with full irrigation, rotational cropping systems that include dryland crops had average ET reductions of 30-40%. Winter wheat or annual forage crops such as triticale are good choices for the dryland phase of these rotations because they use residual water and nutrients from irrigated crops and have lower production risk than dryland summer grain crops like corn.  Irrigated corn produced after a dryland crop had higher yields and water use efficiency than continuous corn, illustrating the benefits of crop rotation to increase crop water productivity. Partial season irrigation cropping systems were evaluated using alfalfa and alfalfa/grass mixes.  When irrigation of alfalfa was terminated after the first hay harvest, annual ET was reduced by more than 40% while yield was only reduced by 30%, reflecting increased crop water productivity.