Work

Synthesis of a calcium alginate hydrogel-modified phosphorus-enriched Douglas fir biochar controlled-release fertilizer

Year: 2026

Type: article

Abstract: Enhanced fertilizer efficiency is crucial for sustainable crop production and food security. Conventional soluble fertilizer formulations suffer from low use efficiency and rapid nutrient release. Here, P-enriched Douglas fir biochar (PBC) was synthesized by reacting CaCl2 and KH2PO4, precipitating Ca3(PO4)2 onto biochar. This was further modified with calcium alginate hydrogel (CA@PBC) for use as a potential controlled-release fertilizer. Ca2⁺-crosslinked alginate forms a resilient hydrogel integrated with biochar, synergistically enhancing plant nutrient and soil water retention, reducing nutrient dissolution, and improving soil health. PBC and CA@PBC were characterized by FTIR, XRD, SEM, XPS, elemental analyses, and BET surface area measurements. Calcium phosphate and minor hydroxyapatite precipitated at pH 10 on PBC. Fixed-bed column leaching experiments in water performed for 20 days at ambient temperature showed prolonged phosphate release from CA@PBC-treated soil versus PBC-treated soil. PBC-treated soil leaches phosphate slower than TSP-treated soil. Greenhouse pot experiments using corn as a test crop were conducted for 35 days, comparing plant growth in soil promoted by CA@PBC, PBC, BC, and triple superphosphate (TSP) reference fertilizer versus unamended soil. Plant growth at a 50 kg P2O5 ha⁻¹ nutrient rate application showed ~16.1% higher height and ~16.4% greater P uptake with PBC than TSP reference fertilizer, whereas CA@PBC showed ~1.2% lower height and ~8.1% lower P uptake compared to TSP. An extended greenhouse period may reveal benefits of hydrogel-modified CA@PBC, if its controlled-release properties can be matched to the plant growth cycle nutrient needs. CA hydrogel and PBC change P-release, enabling a dual-mode future release system.

Source: Biomass and Bioenergy

DOI: 10.1016/j.biombioe.2026.109564