## 3 Results
### Relationships between Microbial Residues, Amino Sugars, and the Biochemical Properties of the Soil  
The correlation matrix between microbial neccomass and soil biochemical properties is shown in Table 4. Soil pH showed a significant and negative correlation with GluN (r = \(-\)0.967), MurN (r = \(-\)0.996), total AS (r = \(-\)0.963), bacterial residues (r = 0.996), and total microbial residues (r = \(-\)0.974); however, it correlated only slightly with galactosamine (r = \(-\)0.937) and fungal residues (r = \(-\)0.939). Microbial biomass (MBC and MBN) correlated significantly and positively with GalN, GluN, MurN, total AS, bacterial residues, fungal residues, and total microbial residues; except for fungal residues, with which it correlated only slightly (r = 0.936). Aboveground plant biomass also showed a significant and positive relationship with GluN (r = 0.956), MurN (r = 0.989), bacterial residues (r = 0.989), and total microbial residues (r = 0.964), but only slightly correlated with GalN (r = 0.913), total AS (r = 0.948), and fungal residues (r = 0.964). Moreover, DOC significantly and positively correlated with GalN (r = 0.953), GluN (r = 0.980), MurN (r = 0.998), total AS (r = 0.976), bacterial residues (r = 0.994), fungal residues (r = 0.954), and total microbial  
Figure 5: Functional relationship between aboveground plant biomass and nitrogen rate (**a**); aboveground plant biomass and soil organic carbon (**b**); aboveground plant biomass and total nitrogen (**c**). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Parameter** & **Treatment** & **2014** & **2015** & **2016** & **2017** & **2018** \\ \hline \multirow{3}{*}{Total nitrogen (g kg\({}^{-1}\))} & No-N & 0.95 \(\pm\) 0.02 a & 0.95 \(\pm\) 0.03 a & 0.96 \(\pm\) 0.06 b & 0.98 \(\pm\) 0.04 c & 1.01 \(\pm\) 0.11 c \\  & Low-N & 0.96 \(\pm\) 0.01 a & 0.98 \(\pm\) 0.04 a & 0.99 \(\pm\) 0.03 b & 1.06 \(\pm\) 0.09 b & 1.11 \(\pm\) 0.05 b \\  & Medium-N & 0.98 \(\pm\) 0.01 a & 1.00 \(\pm\) 0.02 a & 1.08 \(\pm\) 0.16 a & 1.14 \(\pm\) 0.07 a & 1.23 \(\pm\) 0.03 a \\  & High-N & 0.99 \(\pm\) 0.03 a & 1.03 \(\pm\) 0.04 a & 1.11 \(\pm\) 0.07 a & 1.19 \(\pm\) 0.04 a & 1.28 \(\pm\) 0.01 a \\ \hline \multirow{3}{*}{Ammonium (mg kg\({}^{-1}\))} & No-N & 0.78 \(\pm\) 0.01 b & 0.78 \(\pm\) 0.01 b & 0.76 \(\pm\) 0.02 c & 0.77 \(\pm\) 0.01 c & 0.77 \(\pm\) 0.03 c \\  & Low-N & 0.78 \(\pm\) 0.02 b & 0.80 \(\pm\) 0.01 b & 0.84 \(\pm\) 0.02 b & 0.86 \(\pm\) 0.02 b & 0.88 \(\pm\) 0.01 b \\  & Medium-N & 0.87 \(\pm\) 0.02 a & 0.96 \(\pm\) 0.02 a & 1.10 \(\pm\) 0.01 a & 1.17 \(\pm\) 0.03 a & 1.20 \(\pm\) 0.03 a \\  & High-N & 0.91 \(\pm\) 0.01 a & 1.03 \(\pm\) 0.02 a & 1.16 \(\pm\) 0.02 a & 1.23 \(\pm\) 0.02 a & 1.25 \(\pm\) 0.01 a \\ \hline \multirow{3}{*}{Nitrate (mg kg\({}^{-1}\))} & No-N & 4.73 \(\pm\) 0.14 c & 4.74 \(\pm\) 0.11 c & 4.68 \(\pm\) 0.02 c & 4.71 \(\pm\) 0.22 d & 4.70 \(\pm\) 0.09 d \\  & Low-N & 4.73 \(\pm\) 0.11 c & 4.76 \(\pm\) 0.13 c & 5.06 \(\pm\) 0.09 c & 7.70 \(\pm\) 0.14 c & 7.92 \(\pm\) 0.16 c \\ \cline{1-1}  & Medium-N & 5.07 \(\pm\) 0.07 b & 7.89 \(\pm\) 0.07 b & 9.98 \(\pm\) 0.11 b & 12.45 \(\pm\) 0.23 b & 12.99 \(\pm\) 0.33 b \\ \cline{1-1}  & High-N & 6.05 \(\pm\) 0.12 a & 9.21 \(\pm\) 0.29 a & 13.85 \(\pm\) 0.36 a & 17.51 \(\pm\) 0.47 a & 19.18 \(\pm\) 0.35 a \\ \hline \hline \end{tabular} Mean values marked by different letters within the same column and parameter are significantly different from each other at 0.05 probability level.  
\end{table} 
Table 3: Effects of inorganic nitrogen enrichment on total nitrogen, ammonium nitrogen (NH\({}_{4}\)\({}^{+}\)-N), and nitrate nitrogen (NO\({}_{3}\)\({}^{-}\)-N) from 2014 to 2018.  
residues (r = 0.985). Similar to DOC, SOC showed a significant and positive relationship with GalN (r = 0.933), GluN (r = 0.983), MurN (r = 0.988), total AS (r = 0.971), bacterial residues (r = 0.989), fungal residues (r = 0.937), and total microbial residues (0.985).