Purpose <p>This study aims to mitigate arsenic (As) stress in farmland, crucial for sustainable agricultural development. We prepared a carbon-based iron-lanthanum (Fe-La) composite to effectively reduce As bioavailability and promote crop growth.</p> Materials and methods <p>The Fe-La composite was prepared via coprecipitation with an optimal Fe to La molar ratio of 3:2 and the composite was characterized using scanning electron microscopy, X-ray diffraction, Brunauer-Emmett-Teller analysis, and Fourier transform infrared spectroscopy. Pot experiments were conducted to assess the impact of the Fe-La composite on amaranth biomass and As accumulation. The correlation between bioavailable As and plant stress was analyzed to understand the composite’s effectiveness.</p> Results and discussion <p>The Fe-La composite significantly increased amaranth biomass by 130% and reduced As accumulation by 60.7%. Characterization revealed the composite’s composition, including FeO(OH), FeO, and La(OH)₃, which facilitated As removal through chelation, hydroxide precipitation, and external magnetism. The correlation analysis indicated that focusing on bioavailable As is critical for mitigating its impact on plants. The study demonstrates that the Fe-La composite can effectively stabilize As, reducing its bioavailability and mobility in soil. These findings suggest that this composite offers a novel, sustainable, and environmentally friendly remediation technology for As-contaminated soils, enhancing crop growth and reducing As uptake.</p> Conclusions <p>The Fe-La composite shows significant potential as an effective material for the remediation of As-contaminated farmland. By targeting bioavailable As, this approach can improve agricultural productivity and food safety, contributing to sustainable agricultural practices. The study underscores the potential of the Fe-La composite to enhance crop growth and reduce As uptake.</p>