Submitted to: Biological Systems Simulation Group Proceedings
Publication Type: Other
Publication Acceptance Date: March 1, 2006
Publication Date: April 11, 2006
Citation: Baumhardt, R.L., Tolk, J.A., Howell, T.A., Rosenthal, W.D. 2006. Modeling to evaluate irrigation and crop management strategies for maximizing grain sorghum yield and water use efficiency. In: 36th Biological Systems Simulation Conference, April 11-13, 2006, Fort Collins, Colorado. p. 25-26. Technical Abstract: Grain sorghum [Sorghum bicolor (L.) Moench] is a feed grain and potential ethanol feed stock that is grown on the Southern Great Plains under both dryland and irrigated conditions. Because of volatile fuel costs for irrigation and declining well capacity on the Southern High Plains, producers seek cropping practices for use on drylands and with variable irrigation. Our objective was to identify universal sorghum management strategies to maximize yield for variable irrigation levels. Using SORKAM and long-term (1958-1998) weather records we simulated sorghum grain yields on a Pullman soil (fine, mixed, superactive, thermic Torrertic Paleustoll)for all combinations of cultivar maturity (early, medium, late), planting date (15 May, 5 June, 25 June), and plant density (12 and 16 plants m-2) under dryland (rain only), low and intermediate deficit irrigation (rain +irrigation to total 2.5 and 3.75 mm d-1), and full irrigation (5.0 mm d-1) that were applied using a 10 d interval. For 2.5 mm d-1 rain + irrigation levels, simulated grain yields increased with early or medium maturity cultivars planted on 5 June, but for higher irrigation levels of 3.75 and 5.0 mm d-1 sorghum yield increased with mid-May planting of later maturing cultivars. Sorghum yield difference for the rain + irrigation increment increased for the 2.5 mm d-1 and 3.75 mm d-1, but decreased when rain + irrigation was 5.0 mm d-1. The irrigation water use efficiency calculated from the incremental yield increase and water use was less for the 5.0 mm d-1 rain + irrigation than for 2.5 and 3.75 mm d-1 rain + irrigation. Concentrating irrigation water on smaller areas to increase sorghum grain yield was compared with spreading the same amount of water over a larger area. A spatially weighted mean yield was calculated for irrigation strategies ranging from uniform applications at 2.5 mm d-1 and variable applications distributed 2:1 at 3.75 mm d-1and dryland or 1:1 at 5.0 mm d-1 and dryland. Sorghum yields with variable irrigation were as much as 20% greater than the corresponding uniform irrigation strategy.