Irrigation in Midwest: Lessons from Illinois

Abstract
Irrigation is becoming increasingly important in midwestern agriculture. Yet, since the Midwest has traditionally not been heavily irrigated, relatively little has been known about present irrigation water use and irrigation scheduling and efficiency in that region. Questions are arising with greater frequency about irrigation in the subhumid climate of the Midwest, and about the impact of irrigation water use on regional water resources. Biweekly and total irrigation amounts and irrigation‐scheduling practices were monitored at representative sites in central Illinois during the 1988 and 1989 growing seasons. Soil water‐holding capacity (expressed as average field capacity in the root zone) correlates well with total irrigation water use, suggesting that irrigation farmers largely determine their irrigation applications based on some understanding of the water‐holding capacity of their soil. Total irrigation water use varies with weather conditions; year‐to‐year variations are greater than variations from farmer to farmer within any single year. Surprisingly little variation in total irrigation applications is evident between different crop types. Irrigation practices vary because of individual farmer idiosyncracies; these variations have no apparent relation to the physical controls of weather, crop type, or soil type. Irrigation farmers are applying irrigation water on corn and soybean crops in amounts and timing that are in general alignment with evaporative demand and with rainfall. The irrigation sites observed in this study may serve as an analogue for gaining greater understanding of irrigation throughout the Midwest.

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