Does open access promote interdisciplinary knowledge flow? A Quasi-Natural experiment of journal transitions to fully OA in agronomy

• Open Access (OA) significantly broadens the interdisciplinary citation scope across topics, subfields, fields, and domains. • Journal Transitions to Fully OA causally enhance interdisciplinary knowledge diffusion. • OA increases article visibility via social and public media platforms, facilitating indirect pathways for interdisciplinary impact. Interdisciplinary knowledge diffusion is critical for addressing complex scientific and societal problems, yet rigid disciplinary boundaries often constrain citation flows across fields. Open Access (OA) has been advocated as a mechanism to improve research visibility and accessibility, but its effect on interdisciplinary citation remains insufficiently examined. This study evaluates the impact of OA on the breadth of interdisciplinary knowledge dissemination. Exploiting a quasi-natural experiment stemming from journal transitions to fully OA in the field of agronomy (2000–2024), we analyze over 57,000 articles and 1.5 million citing records using a multilayer disciplinary classification system. Employing negative binomial regressions and difference-in-differences estimations, we find that OA significantly broadens the disciplinary scope of citations at the topic, subfield, field, and domain levels. Mechanism analysis indicates that OA enhances dissemination via social media and public platforms, facilitating greater knowledge spillovers. These results emphasize OA’s institutional function in advancing both research accessibility and interdisciplinary knowledge convergence.