3.4. Interaction of diffuse N loading with soil parameters at a depth of 0–20 cm
The spatial relationships of the eight soil parameters with diffuse N loading in the top 20-cm surface layer were analyzed in each sub-basin (Fig. 5). Because the NO3–N loading was much lower, the TN loading was used to analyze the spatial correlations with soil properties. The sub-basins were categorized in four groups so that the impact of land use distribution was identified. The spatial correlations of soil property with diffuse N loading for the four dominant types of land use considered were analyzed. Overlaying the spatial distribution of diffuse N loading with the land use, it was found that most of the diffuse N was discharged from farmlands. So, the linear correlations of soil parameters with N loading in the upland and paddy rice sub-basins were calculated, respectively.