Surface runoff due to LEPA and spray irrigation of a slowly permeable soil

Surface runoff during low energy precision application (LEPA) and spray spr inkler 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 m aintain 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 th e 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 hig h-yield irrigated grain sorghum in the southern Great Plains. LEPA double-e nded socks and spray heads with flat, medium-grooved deflector plates were both spaced 1.52 m apart over alternate furrows. Runoff was measured volume trically in steel tanks from three wheel track and three non-wheel track fu rrows in each plot. No sprinkler runoff occurred in any treatments with the 40% irrigation amount and with the spray/diked combination. Two-year; seas onal average runoff from the spray/undiked combination with 100% irrigation was 12% of the applied water: For the LEPA/diked combination with 100% irr igation, 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/un diked combination. A drought occurred during the early part of the 1998 cro p season, and grain yields were significantly reduced both with and without furrow dikes for the LEPA sprinkler method.