Fertilizer Nitrogen Application for Short-Day Onion Production: From Field to Table

Long growing seasons, relatively shallow root system, coarse textured soils, and variability of the subtropical environmental conditions of the southeastern U.S. create challenges for nitrogen (N) fertilizer management of short-day onions. The objectives of this study were: (i) to evaluate the impact of fertilizer N rates on the yield and bulb quality of three short-day onion cultivars grown under the subtropical conditions of the southeastern U.S., and (ii) to assess the impact of fertilizer N rate for short-day onions on consumers' preference. Field experiments were conducted in 2019 and 2020 at the Vidalia Onion and Vegetable Research Center at the University of Georgia located in Lyons, GA, in which a two factorial experimental design of five fertilizer N rates (84, 101, 117, 134, and 151 kg of N ha(-1)) and three short-day onion cultivars (Sweet Agent, Vidora, and Quick Start) was evaluated in a randomized complete block design. During both growing seasons, rainfall events directly impacted soil mineral N content. While soil mineral N availability increased with fertilizer N application, there was no significant difference among fertilizer N rate treatments due to rainfall distribution in both years studied, except at bulb initiation when the application of 117 kg of N ha(-1) sustained soil mineral N availability that maximized with the application of 128 kg of N ha(-1). Onion total yield averaged 37,365 kg ha(-1) in 2019 and 34,699 kg ha(-1) in 2020. In general, colossal, jumbo, and medium-sized onions represented 7%, 76%, and 17% of total yield, respectively. Jumbo-sized onions are of most interest to growers due to their high value, and the yield of jumbo-sized onions was maximized with 158 kg of N ha(-1) in 2019 and with 138 kg of N ha(-1) in 2020. Bulb bacterial rots were not impacted by fertilizer N rate treatments. Contrarily, bulb gallic acid (GAE) linearly increased and pyruvic acid quadratically increased with the application of fertilizer N rate. Ultimately, a taste panel indicated that sensory characteristics were also not affected by different rates. Overall, a fertilizer N rate application of 117 to 134 kg of N ha(-1) could sustain soil mineral N availability without impacting yield; however, an investigation on the timing of application should be conducted to determine a fertilizer N strategy that will promote optimum yield, bulb quality, flavor, and consumer acceptability.

Automated summary

This study evaluated the impact of fertilizer nitrogen levels on the yield, bulb quality, and consumers' preference of short-day onions grown under subtropical conditions in the southeastern U.S. The results showed that nitrogen levels had a significant effect on yield and bulb quality, but did not affect consumers' preference. Additionally, the appropriate nitrogen application rate could sustain soil mineral nitrogen availability.