Wheat Development as Affected by Deficit, High Frequency Sprinkler Irrigation1

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Abstract
An important limitation to wheat production worldwide is insufficient water. Therefore, it is important to know how the crop responds physiologically to water stress. The present study was conducted to determine the effect of various irrigation rates on wheat development. Variable irrigation treatments were initiated at pre‐ or early‐boot stage of Fielder spring and Nugaines winter wheat (Triticum aestivum L. em. Thell.) grown on sandy (mixed, mesic, Xeric Torripasamments) and loam (coarsesilty, mixed, mesic Xerollic Camborthids) soils. Different amounts of irrigation water were applied by the line source technique. Daily irrigation near the line source was equivalent to 1.00 (loam) or 1.15 (sand) times estimated evapotranspiration (ET). Pan evaporation (EP) was used to estimate ET as ET = 0.95 EP. On sandy soil, stress symptoms were first observed in plants receiving the least irrigation water (23 % estimated ET) 2 weeks after treatments were initiated. Symptoms included decreased number of green leaves, shorter plants, fewer heads, increased specific leaf weight and increased leaf‐stem dry weight ratios. Head growth rates were from 8.2 to 15.6 mg·head−1day−1, at the lowest and highest applications, respectively. Reproductive growth rate, crop growth rate, and partitioning to reproductive growth increased with increased irrigation. Effects of decreased irrigation were less on loam soil than on sandy soil. Stress symptoms did not appear until late in the growing season. There were significant differences in plant height, total plant weight, and head weight between the plots receiving highest and lowest irrigation rates (100 vs. 20 % estimated ET). Results indicate that normal growth and yield of wheat grown on sandy soil require irrigations that approach ET. However, on loam soil irrigation amounts can be decreased 40 to 50 % without affecting developing of plant parts.