Engineering pH-Responsive trans-Ferulic Acid/κ-Carrageenan Beads for On-Demand Micronutrient Delivery in Plants

Micronutrient deficiencies in soils are a critical challenge in agriculture, particularly in acidic soil environments where nutrient availability is strongly limited by fixation, leaching, and altered metal speciation. These constraints contribute to inefficient nutrient uptake and reduced crop yields. Conventional micronutrient supplementation methods are often inefficient, environmentally harmful, and unsustainable, underscoring the need for smarter delivery systems tailored to soil pH conditions. In this study, we developed biodegradable, pH-responsive microbeads from {kappa}-carrageenan ({kappa}-CG) and trans-ferulic acid (TFA) for targeted micronutrient release. The {kappa}-CG-TFA microbeads were synthesized via an eco-friendly process and optimized for size, morphology, stability, and nutrient retention. Characterization confirmed the successful incorporation of functional groups, while swelling, degradation, and release studies demonstrated efficient delivery of essential micronutrients (Mn2+, Zn2+, Cu2+, and Fe3+) under acidic conditions (pH 4.0), mimicking acidic soil environments. The inherent antioxidant activity of TFA conferred strong radical-scavenging capacity, further enhancing its functionality. Soil water and plant growth assays revealed that the microbeads improved micronutrient availability, significantly increased chlorophyll content and leaf area, promoted vigorous seedling growth, and caused no phytotoxic effects. Collectively, these findings establish {kappa}-CG-TFA microbeads as a promising, eco-friendly platform for sustainable micronutrient delivery and stress reduction, thereby improving crop productivity in agriculture.