Development of a salicylic acid-encapsulated zeolite–seaweed biochar composite for sustainable agricultural applications

Abstract

Contemporary agriculture faces critical challenges including declining soil fertility, climate variability, and environmental degradation due to synthetic agrochemicals, necessitating sustainable alternatives that maintain productivity while reducing ecological impact. This study developed and evaluated a salicylic acid-encapsulated zeolite–seaweed biochar nanocomposite (2 : 1 ratio) for enhanced crop performance. Sargassum-derived biochar was pyrolyzed at 450 °C and combined with a clinoptilolite zeolite, achieving a cation exchange capacity of 148.7 ± 6.3 cmol kg⁻¹. Wet impregnation achieved a 92.4% ± 1.8% loading efficiency, yielding 462.0 ± 8.6 mg SA per g of the composite. The composite was characterized using FTIR, XRD, BET, and SEM analyses, confirming its surface functionality and high loading capacity. The physicochemical properties of the prepared biochar composite were investigated and discussed. The total carbon content (33.50%), EC (2.30 dS m⁻¹), and pH (7.78). Particle characterization revealed a mean size of 1289 ± 41 nm, a polydispersity index of 0.23 ± 0.02, and a zeta potential of −18.3 ± 0.4 mV, indicating excellent stability. Controlled release analysis demonstrated 12.7% ± 0.8% SA release in 15 minutes versus 78.4% ± 2.1% for free SA, with 94.7% ± 3.1% cumulative release over 48 hours. Kinetic modeling showed anomalous transport (n = 0.52, R² = 0.992), indicating diffusion-relaxation mechanisms. Accelerated stability testing confirmed 96.2% ± 1.5% SA retention after six months. Field validation with watercress demonstrated 29.5% higher germination (92.3% ± 2.1%), 31.4% increased plant height, 37.4% yield improvement, 50% enhanced nitrogen use efficiency (91.8%), and 42% higher α-amylase activity. Environmental benefits included 39.2% reduced nitrate leaching and 28.7% improved soil water retention. The composite represents a sustainable and multifunctional amendment, successfully integrating controlled phytohormone delivery with soil conditioning for enhanced agricultural performance and environmental stewardship. The encapsulation method demonstrated excellent sustainability credentials across multiple green chemistry frameworks, including AGREE, BAGI and RGB12 methods, underscoring its adherence to both green analytical chemistry principles and the broader white analytical chemistry paradigm.