Characteristics and mechanisms of phosphorus adsorption-desorption in soil aggregates during cut slope restoration

Soil phosphorus (P) effectiveness and sustainability play a crucial role in influencing the ecological restoration process of cut slopes. However, the P adsorption-desorption characteristics of soil aggregates during the ecological restoration of cut slopes remain unclear. We selected three roadside slopes that have undergone ecological restoration for 7, 11, and 14 years, respectively, in Songpan County on the eastern Tibetan Plateau in China. We determined the characteristic parameters of P adsorption-desorption in soil aggregates using isothermal adsorption-desorption experiments. X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) were conducted to characterize the mineral and functional group properties of soil aggregates. The results showed that the P adsorption-desorption capacity of soil aggregates increased with the restoration years. Microaggregates (<0.25 mm) were higher adsorption-desorption capacity than that of macroaggregates (>0.25 mm). Soil organic matter (SOM), available phosphorus (AP), free iron oxide (FeDCB), DCB ), and free aluminum oxide (AlDCB) DCB ) were the driving factor of P adsorption. In addition, total phosphorus (TP), AP, pH, SOM, FeDCB, DCB , and Al DCB played key roles in P desorption. SOM, AP, and Al DCB affected indirectly FeDCB, DCB , while SOM and TP affected indirectly pH, consequently affecting adsorption-desorption. Calcite was involved in P adsorption by soil aggregates. The ligand exchange between the hydroxyl group in montmorillonite and P in the aqueous phase may the key adsorption-desorption process. The current study provides a scientific basis for promoting the effectiveness and sustainability of soil P in cut slope restoration.