Effect of long-term reclamation on soil quality in agricultural reclaimed coastal saline soil, Eastern China

Purpose The assessment of soil quality related to different reclamation years and land use/cover types is the key parameter to evaluate the success of reclamation activities in coastal saline soil. Materials and methods Soil samples were collected from natural bare flat and coastal wetlands that have been reclaimed for different times (7, 32, 40, and 63 years) to investigate the change in soil quality during the process of reclamation in this study. Soil quality was evaluated using a soil quality index (SQI), which was calculated by the selected minimum dataset (MDS) and the technique for order preference by similarity to ideal solution (TOPSIS) methods. Results and discussion Soil water content (SWC), bulk density (BD), electrical conductivity (EC), and pH were observed significantly decreased whereas soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), urease (URE), and acid and alkaline phosphatase (ACP and ALP) activities notably increased after 60 years of reclamation. However, amylase (AMY) activity increased first and then decreased, and dehydrogenase (DEH) activity showed weak differences within 60 years reclamation. Further, TN, EC, AMY, and ACP activity were in the MDS with 12 soil properties as soil quality indicators. The SQI values varied from 0.05 in the bare flat soils to 0.86 in the soils after 63 years of reclamation and improved with increasing reclamation years. In addition, the SQI values of different land use/cover types were in the order of bare flat (0.07 +/- 0.03) < uncultivated land (0.22 +/- 0.16) <Spartina alterniflora(0.25 +/- 0.16) < fishpond (0.57 +/- 0.10) approximate to wheat land (0.58 +/- 0.08) approximate to broad bean land (0.58 +/- 0.07) < rape land (0.73 +/- 0.15). Conclusions Soil quality improved with the increase of reclamation years. Additionally, low levels of TN and high concentrations of EC were the primary constraints restricting soil quality in bare flat and soil in the early stage of reclamation, whereas AMY activity was the main obstacle after 30 years of reclamation.