Surface runoff during low energy precision application (LEPA) and spray sprinkler irrigation of diked and undiked furrows was measured from 20-m-long plots on a slowly permeable, Pullman clay loam. The control treatment (100 irrigation) was sufficient irrigation, applied in 25 mm applications, to maintain the plant available water level in the 1.4-m-deep profile at 75 or more. Deficit irrigation treatment plots received 0, 40, 60, and 80 of the control treatment amount on the same day. The plots were cropped to grain sorghum, and the field had a uniform 0.25 slope in the direction of the 0. 76-m spaced furrows. Cultural practices were similar to those used for high-yield irrigated grain sorghum in the southern Great Plains. LEPA double-ended socks and spray heads with flat, medium-grooved deflector plates were both spaced 1.52 m apart over alternate furrows. Runoff was measured volumetrically in steel tanks from three wheel track and three non-wheel track furrows in each plot. No sprinkler runoff occurred in any treatments with the 40 irrigation amount and with the spray/diked combination. Two-year seasonal average runoff from the spray/undiked combination with 100 irrigation was 12 of the applied water For the LEPA/diked combination with 100 irrigation, runoff was about twice that of the spray/undiked combination with a two-year seasonal average of 22. With the LEPA/undiked combination, two-year average seasonal runoff percentages were 37, 46, and 52 for the 60, 80, and 100 irrigation amounts. For 1997, a year of near average rainfall, grain sorghum yields were significantly reduced by runoff for the LEPA/undiked combination. A drought occurred during the early part of the 1998 crop season, and grain yields were significantly reduced both with and without furrow dikes for the LEPA sprinkler method.
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