[Assessment of Soil Quality in Coastal Tidal Flat Reclamation Areas Based on MDS-TOPSIS Model]

Investigating the change of soil quality during reclamation can provide scientific guidance for desalinization, fertilization, etc. Soil samples were collected from natural tidal flat areas (0 years) and coastal tidal flat reclamation areas with different reclamation years (5, 30, 38, and 61 years) to assess the changes in soil quality after 60 years of reclamation. Soil quality was evaluated using a soil quality index (SQI), which was calculated by the selected minimum data set (MDS) and TOPSIS method. The ratio of clay content (CLAY), soil salt content (SSC), soil organic carbon (SOC), total potassium (TK), and bulk density (BD) were selected as soil quality indicators involving soil physical and chemical properties based on the MDS. The results showed that soil particle size tended to refine gradually with the continuous decrease of sand content and increase of silt and clay content. Simultaneously, soil water content (SWC) and soil BD decreased gradually during the reclamation period. Additionally, SSC, pH and sodium adsorption ratio (SAR) decreased significantly with increase in reclamation years, whereas the nutrients and available nutrients were accumulated gradually, such as soil organic matter (SOM), total nitrogen (TN), total phosphorus (TP), available nitrogen (AN), and available phosphorus (AP). However, C/N, TK and available potassium (AK) showed a decrease with increasing reclamation years, and the cation exchange capacity (CEC) showed a trend of first decrease and then increase. Finally, SQI values varied from 24.06 in the bare flat soils to 63.08 in the soils after 63 years of reclamation, and showed that bare flat (20.04±11.48) < reclamation for 5 years (29.33±10.65) < reclamation for 30 years (51.52±8.76) ≈ reclamation for 38 years (49.98±10.75) < reclamation for 61 years (58.37±3.15), which has gone through approximately three stages of "initial stability-rapid improvement-relative stability." Soil CLAY content had the highest obstacle degree towards SQI among the selected MDS indicators, followed by SSC, SOM, TK, and SWC, and thereby the lower clay content and higher salt content were the main obstacle factors for promotion of soil quality in reclamation areas.