Reddy, S., Extension Educator, University of Idaho Extension, Washington County
Klauzer, J., Field Representative, Clearwater Supply, Inc.
Neufeld, J., Extension Educator, University of Idaho Extension, Canyon County

ABSTRACT

An applied research and demonstration project was installed in onion fields that used furrow or drip irrigation. Fields were not replicated but were installed for five consecutive years to reveal seasonal influences. Production inputs, based on Southern Idaho Fertilizer Guide for Onions (CIS 1081) and Nutrient Management for Onions in the Pacific Northwest (PNW 546) were measured, and soil, water, and onion tissues were sampled for nitrogen (N). Onion yields and bulb sizes were recorded and the fields then compared for water and N use efficiency (WUE and NUE). Beginning in 2005, a Furrow Treatment was introduced into the project that allowed for N fertilizer applications based on the soil sample recommendations in CIS 1081 and PNW 546. This treatment continued through 2007. WUE and NUE were calculated and compared for all fields. Yields were high throughout the project and were often very close among the fields within a season. The Furrow Treatment fields used approximately 40% less N fertilizer than the Furrow Control and produced yields that were only 4.1% to 5.2% less than the control. The Drip field produced the best WUE and NUE when compared to the Furrow Control. Furrow Treatment yield for 2007 fit close to the high range of the Preplant Yield Response Curve in PNW 546 indicating sufficient N availability. The project showed that high onion yields can be produced with reduced N fertilizer applications. Demonstration of efficiency through this project can help growers keep production costs down, maintain high yields, and minimize N leaching into water supply.
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