Background and aims <p>Phenotypic plasticity in associations enables higher resource use efficiency and niche complementarity. This study aims to (1) examine the phenotypic plasticity of soybean functional traits to relay-cropping under drought conditions and (2) evaluate different soybean genotypes and their interactions.</p> Methods <p>A preliminary investigation comprised field experiments in micro-plots in non-irrigated conditions performed for two years (2022 and 2023) to examine trait responses to barley relay-cropping for four soybean genotypes compared to sole crops. In 2022, we experienced a record-setting drought that highly impacted the soybean yield. Ten above- and below-ground functional traits related to light interception, resource allocation and soil exploration were measured at barley harvest and one month after, at the reproductive stage.</p> Results <p>Our results showed that relay-cropping can exacerbate drought stress and, consequently, competition for water between crops. This led to phenological delay and growth abortion. However, root functional traits, such as lateral root mean angle, specific root length and root nodules densities, were higher in relay-cropping, demonstrating plant response to water stress and competition.</p> Conclusion <p>Soybean genotypes showed a plasticity of root functional traits to respond to competition and water stress. Agricultural practices (timely irrigation and/or adapting relay-cropping design) could modulate water stress, and appropriate cultivars would allow relay-cropped soybeans to sustain temporally dry conditions.&#xa0;</p>