A field trial on green onion crops in the autumn of 2020 transpired at a private farm in the District Al-Saniyah, Al-Diwaniyah Governorate, Iraq. The presented study aimed at characterizing green onion (Allium cepa L.) plants with NPK fertilization and foliar application of hornwort extract for growth and yield traits. In this experiment, the first factor comprised three NPK levels (0, 50%, and 100%) of NPK (150:100:150 kg ha^-1) recommended fertilizer added to the soil, while the second factor included the foliar application of hornwort extract with two different concentrations (0, 20 ml L^-1). The experiment in a randomized complete block design (RCBD) with factorial arrangement had three replications. Consequently, the recommended dose of NPK (100%) and spraying hornwort extract at 20 ml L^-1 revealed a significant increase in the studied traits, i.e., plant height, length of the longest tubular leaf, number of leaves, fresh weight of tubular leaves, number of bulbs per plant, weight of the bulb, the diameter of the bulb, leaf chlorophyll content, bulb carbohydrate content, leaf carotenoid content, and plant yield. The interactions of both factors also showed a favorable effect on the mentioned traits in green onion.

Keywords: Onion (Allium cepa L.), NPK levels, Ceratophyllum demersum L. extract, growth traits, yield variables, biochemical traits, total chlorophyll, carotenoid, carbohydrate content

Key findings: The recommended NPK fertilization dose resulted in better vegetative growth, yield, and biochemical traits in green onion plants. Also, the exogenous application of the hornwort extract (20 ml L^-1) provided better effects for all the quantitative features. Furthermore, the combined application and interaction of both factors with the highest doses caused favorable impacts on green onion plant characteristics.