Compared to the top layer, the correlations with N loadings in
the upland basin were opposite. The higher N loading content
indicated a higher AN, TN, SOC, and S loading. In the paddy rice
sub-basins, the correlations were still slightly negative as they
were in the top layer. The higher contents of four non-heavy metal
soil indices did not cause greater N loading. Because the contents
were lower in the top level, there should be a threshold content of
four non-heavy metal indices which the correlation developed in
the reverse direction. The TN content at this depth did not exhibit a
strong correlation with the diffuse N loading. Except the Pb, the
other three metal indicators showed similar trends to those
observed in the surface layer. The change in the Pb correlation
direction indicated that there was also a turning point in the Pb
content that can affect the pollution loading. Because the
correlation coefficient (R2) value in the surface was much bigger
than the subsurface, it can be hypothesized that the top layer soil
played a more important role in diffuse N loading than the
subsurface.