Bifunctional chitosan-modified urea–formaldehyde fertilizer for soil restoration and slow, sustained nitrogen release

Nutrient supply and heavy metals (HMs) remediation are key for agricultural development. However, achieving both goals with a single agent is challenging. In this study, bifunctional chitosan-modified urea–formaldehyde (CSUF) gel beads having a three-dimensional structure were developed to serve as a slow-release nitrogen fertilizer and a HM fixative for soil treatment. The adsorption capacities for Cd(II), Cu(II), and Cr(VI) reached 49.8, 6.63, and 40 mg/g, respectively. Further, over 10 d, CSUF removed 86 %, 93.28 %, and 91.32 % of Cd(II), Cu(II), and Cr(VI), respectively, from the soil while releasing 40 % of the nitrogen. Crucially, the adsorbed HM ions were not re-released, although the nitrogen continued to be released for 15 d. Plant growth experiments indicated that CSUF promoted mung bean sprout growth, increasing the dry and fresh weights by 33.33 % and 47.83 %, respectively, and significantly mitigating HM stress effects by reducing the Cd(II), Cu(II) and Cr(VI) content in the plant tissue by 89.28 %, 92.08 %, and 94.97 %, respectively. Overall, the bifunctional fertilizer shows potential for promoting sustainable agriculture.