Artificial humic acid mediated migration of phosphorus in soil: Experiment and modelling.

[Display omitted] • AHA addition can enhance the adsorption capacity of soil phosphorus. • AHA decreases phosphorus loss under freeze-thaw condition, and the longer the freeze-thaw time, the better the effect. • Alkaline conditions and high ionic strength promote the migration of soil phosphorus through electrostatic repulsion. • Two-site model results fit well with breakthrough experimental data. The problem of soil nutrient loss has become increasingly serious in recent years, and the problem of soil "thinning" has led to a gradual decrease in the soil's ability to fix phosphorus (P). In order to effectively alleviate the loss of soil nutrients and improve the ability of soil to fix phosphorus, artificial humic acid (AHA) is a promising material. Therefore, this paper focuses on the effect of AHA addition on the transport behavior of P in soil. Column experiments were designed considering four environmental influences (AHA addition, freeze-thaw cycles, background pH and ionic strength) and two types of soils (black soil and saline soil). In order to clarify the mechanism of its migration behavior, we used characterization methods, Density functional theory (DFT) calculations and the two-site nonequilibrium transport model (TSM) models. The results showed that AHA effectively enhanced the P fixation ability in the soil. Specifically, with the increase of AHA concentration, the soil formed an envelope complex and further enhanced the absorption and fixation ability of soil P through complexation and electrostatic action. We found an interesting phenomenon that AHA can enhance the adsorption of P in soil as the number of freeze-thaw days increased, contrary to our initial hypothesis that freezing and thawing would lead to a decrease in the ability of AHA-added soils to fix P. At lower pH, the protonation reaction of functional groups on the surface of AHA molecules led to the neutralization of OH– which in turn enhanced the adsorption of P in soil. The lower ionic strength weakened the electronegativity of the soil and enhanced the fixation of P in soil. Meanwhile, the TSM could better simulate the P transport behavior under the above-mentioned condition. This study elucidated the transport behavior of P in black and saline soils with the introduction of AHA, which could effectively clarify the environmental risk caused by P loss and improve the ecological benefits of AHA. [ABSTRACT FROM AUTHOR]