Fig. 1. Schematic diagram showing the sampling sites of agricultural soil that was reclaimed from typical saline-sodic soils in Northeastern China.

The area in brown yellow represents the Songnen Plain, one of the three major regions with saline-sodic soil in the world. The solid circle in red within the Songnen Plain refers to the long-term reclamation experiment field of the Da’an Sodic Land Ecological Experiment Station of Northeast, Chinese Academy of Sciences. Soil samples were collected from the Solonetz saline-sodic field (upright panel) that contains no vegetation cover for >40 years as a control, and farmland (downright panel) that has been maintained for maize-watermelon rotation system more than 40 years.