Aminated rice straw/oxidized sodium alginate/iron(III): Synthesis and slow-release properties of a biomass-based material used as base fertilizer

To develop sustainable agriculture and improve the fertilizer utilization value of straw resources, a biomass-based material aminated rice straw/oxidized sodium alginate/iron(III) (ARS/OSA/Fe3+) with a slow-release function was developed. The preparation conditions were determined as follows: 1.67 g of ARS, 3.33 g of OSA, and 50 mL of distilled water were mixed and stirred at room temperature for 12 h to obtain the ARS/OSA colloid; the colloid was added to 100 mL of Fe(NO3)3 solution at the concentration of 6% and stirred at room temperature for 1 h to obtain the ARS/OSA/Fe3+. ARS/OSA/Fe3+ was the small circular flakes with 2–2.5 mm in diameter and 1 mm in thickness, in which the content of iron was 9.9% by weight. It showed good slow-release performance in soil. The iron(III) release rates of 1-day and 30-days were 2.18% and 64.02%, respectively. Kinetic analysis showed that the release mechanism of ARS/OSA/Fe3+ in soil may be dissolution followed by swelling diffusion and finally dissolution diffusion. The combination of FT-IR, XRD, XPS, DSC, and SEM analysis showed as follows: the amination process occurred on lignin in the rice straw lignocellulose; ARS and OSA were crosslinked to form a polymer with a crosslinked network structure; the ferric elements mainly existed in trivalent form; and the ARS/OSA/Fe3+ was synthesized through the coordination modes of carboxylate anion to iron(III) cations. ARS/OSA/Fe3+ has the potential to be developed as base fertilizers and soil amendments in agricultural production.