CORN IRRIGATION MACROMANAGEMENT AT THE SEASONAL BOUNDARIES – INITIATING AND TERMINATING THE IRRIGATION SEASON

Decisions about when to initiate and terminate the irrigation season are important irrigation macromanagement decisions that can potentially save water and increase net income when made correctly, but can have negative economic consequences when made incorrectly. A combination of nine years of pre-anthesis water stress studies and sixteen years of post-anthesis water stress studies for corn was conducted at the Kansas State University Northwest Research-Extension Center in Colby, Kansas on a productive, deep, silt loam soil. Overall, the pre-anthesis water stress studies suggest that corn grown on this soil type has great ability to handle early-season water stress, provided the water stress can be relieved during later stages. A critical factor in maximizing corn grain yields as affected by pre-anthesis water stress is maximizing the kernels/area. Maintaining a water deficit ratio (well-watered calculated corn water use / sum of irrigation and precipitation) greater than 0.7 to 0.8 or limiting available soil water depletion in the top 4 ft of soil profile to approximately 30% maximized the kernels/area. Overall, the post-anthesis water stress studies suggest that corn yield is nearly linearly related to the amount of crop water use during the post-anthesis period and that total crop water use amounts may average nearly 17 inches. Producers should plan for crop water use during the last 30 and 15 day periods that may average nearly 5 and 2 inches, respectively, to avoid yield reductions. Management allowable depletion during the post-anthesis period should be limited to 45 % of the available soil water for an 8-ft profile on the deep silt loam soils of this climatic region