| Summary: | Delaying the first irrigation is thought to encourage root growth and condition crops for stress later in the season. Our objective was to test this common practice using corn. Field studies were conducted in Tucson, Arizona in 1989 and 1990 in which the first irrigation was applied at the Z 4, or 8 -leaf stages, and then either irrigated or stressed at anthesis. Delaying the first irrigation either restricted or did not influence root growth. Water use during anthesis was increased if the first irrigation was delayed, especially at the 2 to 3-foot depth. Delaying the first irrigation delayed silking by approximately 3 days and decreased the rate of dry matter accumulation. Grain yield was decreased 20% and total plant yield was decreased 14% in 1990 where the first irrigation was delayed past the 2 -leaf stage and the crop was well- watered at anthesis. Timing of the first irrigation did not affect yield if irrigations were withheld at anthesis. Delaying the first irrigation does not appear to condition corn for moisture stress later in the season, and may substantially decrease yield in certain situations.
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