SURFACE RUNOFF DUE TO LEPAAND SPRAY IRRIGATION OF A SLOWLY PERMEABLE SOIL

摘要

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.