<Fig. 5>
The spatial patterns of the SOC changes during the three time periods were presented in Fig. 5. In the first two decades (1980-2000), the areas with relatively large SOC increments (> 5 g kg-1) were mainly distributed in the north (along the Yangtze River) and southwest of the study area, while the areas with relatively large SOC decrements (> 5 g kg-1) were scattered in the northeastern parts (brown areas in Fig. 5a). Changes in the SOC contents in the major croplands of the study area varied from -12.4 to 15.1 g kg-1. In contrast, the SOC contents for most of the study area decreased during the period of 2000-2015; in particular, the areas with SOC decrements > 5 g kg-1 expanded significantly (mainly located in the east, Fig. 5b). A slight decrease in the SOC contents (decrement< 3 g kg-1) across the study area could be intuitively observed (yellow areas), while the increases in SOC mainly occurred in the northeastern, northwestern, and southeastern parts of study area (green areas in Fig. 5b), with a small increment of less than 5 g kg-1. Over the entire 35 years (Fig. 5c), changes in the SOC contents in the topsoil of the major croplands varied from -21.3 to 10.2 g kg-1, and the SOC for most parts of the study area increased, except for that in the southeastern parts (close to Changshu city), where SOC declined significantly (with SOC decrement > 5 g kg-1).

3.4 Probability of SOC increase/decrease