Chitosan and D-fructose 1,6-bisphosphate differ in their effects on soil acidity and aluminum activation

Purpose This study aims to evaluate the effects of chitosan and D-fructose 1,6-bisphosphate (F16BP) trisodium salt on the acidity of selected Ultisols (Ultisol-QY1, Ultisol-QY2, Ultisol-LX, and Ultisol-YT) and their resistance to soil acidification. Materials and methods The effect of adsorbed chitosan and F16BP on soil acidity was evaluated by interacting different concentrations of the organic substrates with 4.0 g soil under different agitation times (2 to 264 h, 200 rpm, 25 °C). Also, the soils were amended with the organic substrate and incubated for 14 days to determine their effects on soil physicochemical properties. Afterwards, the soil solid phases from the adsorption studies and incubated soil were acidified with different concentrations of nitric acid to simulate soil acidification and activate soil aluminum (Al). Results and discussion The adsorption interactions of chitosan and F16BP with Ultisols demonstrated different potentials in their ability to displace mineral-bound hydroxyl groups and ameliorate soil acidity. The R-PO 4 3− group of F16BP was more effective in displacing the hydroxyl groups through a ligand exchange mechanism and thus showed greater ameliorating effect on soil acidity than chitosan. Compared to lime and F16BP, chitosan-treated soils exhibited the least decrease in pH during soil acidification due to the significant improvement in soil pH buffering capacity (pHBC). Specifically, when amended with chitosan, the pHBC of Ultisol-QY1, Ultisol-QY2, Ultisol-LX, and Ultisol-YT was increased by 262.2%, 88.9%, 337.7%, and 320.6% as opposed to 22.1%, 18.4%, 27.4%, and 83.0% for these Ultisols by F16BP, respectively. Thus, F16BP is a better material to improve soil pH, while chitosan is a better option to improve soil pHBC, inhibit soil acidification, and retard the activation of phytotoxic Al 3+ . By the nature of their functional groups, we deduced that F16BP ameliorated soil acidity by displacing the hydroxyl groups on soils due to adsorption of R-PO 4 3− group through ligand exchange mechanism, while chitosan directly improved pHBC by providing abundant R-NH 2 groups to accommodate excess exogenous H + . Conclusions Chitosan is a promising soil amendment material for use in the management of acidic soils due to its high N content and potential to inhibit soil acidification. Given the readily available raw materials and ease of producing chitosan, long-term incubation studies should be carried out to assess the effect of chitosan on soil pH variations, carbon, and N mineralization.