Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 10, 2000
Publication Date: N/A
Interpretive Summary: Runoff from low energy precision (LEPA) and spray irrigation is increasingly recognized as the largest potential water loss for the two sprinkler methods. Furrow diking (basin tillage) reduces or eliminates runoff from sprinkler applied water and rainfall, but this tillage practice is not widely accepted by irrigation farmers in the southern Great Plains. To better quantify sprinkler runoff losses, a field study was conducted to measure the amount of runoff from LEPA and spray irrigation. Runoff was measured both with and without basin tillage or furrow dikes. Furrow diking retained all spray irrigation and rainfall on the field, but erosion of furrow dikes from the high rate LEPA irrigation caused the loss of both irrigation and rainfall. With 100% irrigation for maximum grain yields, runoff as a percent of sprinkler applied water was 0 and 12% for spray irrigation with and without furrow dikes and 22 and 52% for LEPA irrigation nwith and without furrow dikes. Grain sorghum yields from spray irrigation with or without furrow diking were about 1000 lb/ac larger than for LEPA irrigation with furrow diking and 2000 lb/ac larger than LEPA irrigation without furrow diking. The study establishes spray irrigation with furrow diking as the most efficient use of both irrigation and rainfall for summer grain crops in the southern Great Plains. When irrigating for maximum grain yields, furrow diking or some other method of controlling runoff is essential for high efficiency use of both LEPA and spray irrigation.
Technical Abstract: Runoff due to low energy precision application (LEPA) and spray sprinkler irrigation of diked and undiked furrows was measured from 20-m long plots on Pullman clay loam, a slowly permeable soil. 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 by farmers for high yields of 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 all 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 2-year, seasonal average of 22%. With the LEPA/undiked combination, 2-year, seasonal average 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. Grain yields for 1998 were significantly reduced both with and without furrow dikes for the LEPA sprinkler method.