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NITROGEN MANAGEMENT

Nitrogen Effects on Onion Yield Under Drip and Furrow Irrigation

^a USDA-ARS, 2150 Centre Ave., Bldg. D, Suite 100, Fort Collins, CO 80526
^b Colorado State Univ., Arkansas Valley Research Center, 27901 Rd. 21, Rocky Ford, CO 81067. Contribution from USDA-ARS and CSU. The U.S. Department of Agriculture offers its programs to all eligible persons regardless of race, color, age, sex, or national origin, and is an equal opportunity employer

^* Corresponding author (Ardell.Halvorson{at}ars.usda.gov).

Onion (Allium cepa L.) is a high cash value crop with a very shallow root system that is frequently irrigated and fertilized with high N rates to maximize yield. Converting from furrow-irrigated to drip-irrigated onion production may reduce N fertilizer needs, water inputs, and NO₃–N leaching potential. Onion growth and N uptake, fresh yield, and residual soil NO₃–N were determined under drip and furrow irrigation on a clay loam soil with N fertilizer rates from 0 to 224 kg N ha^–1. Onions were sampled bi-weekly from 25 May to 30 August in 2005 and 2006 from each treatment. In 2005, 72% less water was applied with the drip system compared with furrow system, and 57% less in 2006. Onion yields were significantly greater with the drip system. Total marketable fresh onion yield increased with increasing N rate in 2005 only. The drip system had more colossal and jumbo sized onions and less medium sized onions than the furrow system. Biomass production and N accumulation accelerated in mid-June each year with an average total N accumulation (leaves + bulbs) of 121 kg N ha^–1 at final harvest. Irrigation water use efficiency (IWUE) and N use efficiency (NUE) were higher with the drip system than with the furrow system. Residual soil NO₃–N levels were greater in the drip-irrigated treatments after onion harvest in 2005 than in the furrow-irrigated treatments, but soil NO₃–N levels were similar after harvest in 2006. Adjusted gross economic returns (less the cost of N, water, and drip system) were greater with drip irrigation than with furrow irrigation. This study demonstrates that fresh onion yields, potential economic returns, IWUE, and NUE can be improved in Colorado by using drip irrigation for onion production rather than furrow irrigation.

Abbreviations: AN, available N [soil N (0–60 cm depth) + fertilizer N added + irrigation water N] • AVRC, Arkansas Valley Research Center • ET, evapotranspiration • IWUE, irrigation water use efficiency • NFUE, N fertilizer use efficiency • NUE₁, nitrogen use efficiency based on N uptake • NUE₂, nitrogen use efficiency based on fresh onion yield

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Received for publication November 19, 2007.