Onion Response to Nitrogen Fertilization Under Drip and Furrow Irrigation

Authors: Halvorson, Ardell; BARTOLO, MICHAEL - CSU-AVRC, ROCKY FORD, CO; Reule, Curtis; BARRADA, ABDEL - CSU-AVRC, ROCKY FORD, CO

Submitted to: Experiment Station Bulletins
Publication Type: Experiment Station
Publication Acceptance Date: 12/14/2006
Publication Date: 10/1/2007
Citation: Halvorson, A.D., Bartolo, M., Reule, C.A., Barrada, A. 2007. Onion Response to Nitrogen Fertilization Under Drip and Furrow Irrigation. In Colorado Agric. Exp. Sta. Technical Report TR07-14, Colorado State University, Fort Collins, CO. p. 49-53.

Interpretive Summary: Onion is a high cash value crop with a very shallow root system, frequently fertilized with high N rates to maximize yield, and utilizes N fertilizer inefficiently. In 2005, we applied six N rates (0, 40, 80, 120, 160, and 200 lb N/a) to existing N plots previously cropped to chile pepper (2004). A polycoated urea, with a 90 to 120 day release period, was used and applied prior to planting. The N main plots were split to allow irrigation by furrow (normal method) and by a drip system. At the end of the season, a total of 27 inches of irrigation water had been applied with the drip system and 96 inches with the furrow system. Total marketable fresh onion yield increased with increasing N rate in both systems, with less response of onion to N with the drip system compared to the furrow irrigation system. Higher onion yields were obtained with the drip system. Averaged over irrigation system, the percentage of the onion crop that was of colossal size (>4 inch diameter) increased from 5% to 14% with increasing N rate, jumbo size (3-4 inch diameter) which made up 80% of the yield was not affected by N rate, and medium size (2-3 inch diameter) decreased from 14% to 5% with increasing N rate. Adjusted gross economic returns were greater with drip irrigation than with furrow irrigation. This work demonstrates that economic returns can be maintained by using the more efficient drip irrigation system for onion production rather than the inefficient furrow irrigation system. With the drip system, onion yields were maximized with a lower rate of N fertilizer and 72% less irrigation water than with the furrow irrigation system.

Technical Abstract: Onion is a high cash value crop with a very shallow root system that is frequently fertilized with high N rates (>200 lb N/a) to maximize yield. In 2005, we applied six N rates (0, 40, 80, 120, 160, and 200 lb N/a) to existing N plots previously cropped to corn (2000-2003) and chile pepper (2004). The N source was a polycoated urea with a 90 to 120 day release period which was applied prior to planting. The N main plots were split in 2005 to allow irrigation by furrow (normal method) and by a drip system. At the end of the season, a total of 27 inches of irrigation water had been applied with the drip system and 96 inches with the furrow system. Total marketable fresh onion yield increased with increasing N rate in both systems, with less response of onion to N with the drip system compared to the furrow irrigation system. Significantly higher onion yields were obtained with the drip system. Averaged over irrigation system, the percentage of the onion crop that was of colossal size (>4 inch diameter) increased from 5% to 14% with increasing N rate, jumbo size (3-4 inch diameter) which made up 80% of the yield was not affected by N rate, and medium size (2-3 inch diameter) decreased from 14% to 5% with increasing N rate. Adjusted gross economic returns were greater with drip irrigation than with furrow irrigation. This work demonstrates that economic returns can be maintained by using the more efficient drip irrigation system for onion production rather than the inefficient furrow irrigation system. With the drip system, onion yields were maximized with a lower rate of N fertilizer and 72% less irrigation water than with the furrow irrigation system.