Differences in the distribution, availability, and sorption-desorption isotherms of phosphorus fractions in soil aggregates from cut slopes with different restoration methods

The construction of highways and other transportation facilities resulted in a large number of exposed cut slopes, leading not only to the alteration of soil structure but also to phosphorus (P) losses from soils with low utilization rates. These negative effects can result in stunted plant growth and the occurrence of heavy rainfall and earthquakes-associated landslide and mudslide disasters, threatening people's lives. However, few studies have investigated soil aggregates P in cut slopes restored with different methods in the Alpine Mountainous areas of Southwest China. Therefore, three types of cut slopes (cut slopes restored by three-dimensional mesh (TCS), cut slopes restored by galvanized wire mesh (GCS), and cut slopes restored by nature (NCS)) were selected for the study, and the present study aims to assess the total phosphorus (TP), available phosphorus (AP), and P fractions, as well as the P sorption-desorption isotherms in cut slope soil aggregates. The obtained results are as follows: (1) The TP contents in the soil aggregates did not differ significantly between the three types of cut slopes (p > 0.05), In addition, the AP contents and P activation coefficient (PAC) showed significant differences between TCS, GCS, and NCS, while the H2O-Pi, NaHCO3-Po, NaOH-Pi, NaOH-Po, HHCl-Pi, and HHCl-Po contents were significantly different between the three types of cut slopes (p < 0.05); (2) The AP contents in the three types of cut slopes showed a decreasing trend with increasing soil aggregate size from < 0.25 mm to > 5 mm; (3) H2O-Pi, NaOH-Pi, and HHCl-Pi were the main P fractions affecting the AP contents in the study area, among which NaOH-Pi exhibited the greatest effect on the AP contents; (4) The lowest P adsorption of soil aggregates was observed in NCS. The maximum P adsorption (Qm) values of the < 0.25 mm aggregates in TCS and GCS were higher than those of the other soil aggregate sizes. In addition, the trend of P desorption to increase with P adsorption was more obvious in large aggregates than in small aggregates. The present study provides a theoretical basis for P management in cut slope soils restored by different methods in the Alpine Mountainous region of Southwest China. Moreover, it provides some references for improving cut slope restoration and ecological slope protection techniques.