Yield components and agronomic performance of red onion (Allium cepa L.) under foliar application of biostimulants in Andean agriculture

ABSTRACT Red onion (Allium cepa L.) is economically vital in Ecuador, yet yields remain suboptimal. This study evaluated the morpho-agronomic response of red onion to foliar biostimulants (fulvic acids, seaweed extract, amino acids, and Si) applied at two doses every 15 d. Plant height, leaf number, bulb size, yield, and thrips incidence were assessed. The seaweed extract (5 mL L⁻¹) elicited the best performance, followed by amino acids (1.5 g L⁻¹) and fulvic acids (5 mL L⁻¹). These treatments caused significant increases (p < 0.05) in vegetative growth, improving plant height by up to 9.22% and leaf number by 10.68%. Harvest variables similarly improved, with bulb diameter and yield increasing by 6.37% and 6.95% over the control. Notably, while growth promoters enhanced yield, only Si treatments significantly reduced thrips (Thrips tabaci Lindeman) incidence. These results validate biostimulants as a sustainable management strategy to enhance onion productivity and resilience under Andean conditions.