## 4 Discussion  
The long-term single application of film-mulched drip irrigation technology has been proven unfavorable to the storage of soil nutrients; however, several studies have shown that the addition of external organic matter can significantly increase the soil nutrients content. As such, people have advocated and practiced returning organic materials to the field to reduce the application of chemical fertilizers, improve soil fertility and increase \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Sampling Date** & **Treatment** & **MBN/TN** & **DON/TN** & **PON/TN** & **ATN/TN** & **N\({}_{\rm min}\)/TN** \\ \hline \multirow{4}{*}{October 2018} & SM & 1.17 \(\pm\) 0.08 b & 0.74 \(\pm\) 0.29 a & 33.98 \(\pm\) 6.23 a & 35.89 \(\pm\) 6.34 a & 1.86 \(\pm\) 0.09 a \\  & FG & 0.98 \(\pm\) 0.11 b & 0.94 \(\pm\) 0.04 a & 21.77 \(\pm\) 1.43 ab & 23.69 \(\pm\) 1.30 ab & 2.12 \(\pm\) 0.37 a \\  & CK & 0.88 \(\pm\) 0.13 b & 0.71 \(\pm\) 0.26 a & 12.86 \(\pm\) 3.60 b & 14.45 \(\pm\) 3.69 b & 2.20 \(\pm\) 0.41 a \\  & MS & 1.56 \(\pm\) 0.14 a & 0.89 \(\pm\) 0.12 a & 23.07 \(\pm\) 2.61 a & 25.52 \(\pm\) 2.63 a & 2.03 \(\pm\) 0.23 a \\ \hline \multirow{4}{*}{April 2019} & SM & 1.39 \(\pm\) 0.07 b & 0.57 \(\pm\) 0.18 a & 38.34 \(\pm\) 2.13 a & 40.60 \(\pm\) 2.11 a & 3.35 \(\pm\) 0.21 a \\  & FG & 1.36 \(\pm\) 0.14 b & 0.64 \(\pm\) 0.34 a & 19.19 \(\pm\) 1.91 c & 21.19 \(\pm\) 1.97 c & 3.12 \(\pm\) 0.37 a \\  & CK & 0.98 \(\pm\) 0.13 b & 0.33 \(\pm\) 0.09 a & 8.95 \(\pm\) 1.50 d & 10.27 \(\pm\) 1.49 d & 2.98 \(\pm\) 0.18 a \\  & MS & 1.87 \(\pm\) 0.15 a & 0.71 \(\pm\) 0.11 a & 28.36 \(\pm\) 3.46 b & 30.94 \(\pm\) 3.44 b & 3.15 \(\pm\) 0.04 a \\ \hline \multirow{4}{*}{October 2019} & SM & 1.28 \(\pm\) 0.14 a & 0.78 \(\pm\) 0.05 ab & 39.66 \(\pm\) 7.23 a & 41.72 \(\pm\) 7.37 a & 2.41 \(\pm\) 0.13 a \\  & FG & 1.30 \(\pm\) 0.22 a & 0.90 \(\pm\) 0.06 a & 27.70 \(\pm\) 1.36 ab & 29.90 \(\pm\) 1.18 ab & 2.85 \(\pm\) 0.16 a \\ \cline{1-1}  & CK & 1.30 \(\pm\) 0.35 a & 0.70 \(\pm\) 0.01 b & 19.10 \(\pm\) 3.99 b & 21.10 \(\pm\) 4.28 b & 2.78 \(\pm\) 0.18 a \\ \cline{1-1}  & MS & 2.00 \(\pm\) 0.08 a & 0.84 \(\pm\) 0.07 ab & 27.74 \(\pm\) 2.63 ab & 30.58 \(\pm\) 2.57 ab & 2.61 \(\pm\) 0.35 a \\ \hline \end{tabular} Note: values represent mean \(\pm\) standard error. Data with different letters within the same row are significantly different at 5% level.  
\end{table} 
Table 2: Distribution ratio of soil active nitrogen fractions in total soil nitrogen. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & **TN** & **MBN** & **DON** & **PON** & **ATN** & **NO\({}_{\rm 3}\)\({}^{-}\)N** & **NH\({}_{\rm 4}\)\({}^{+}\)-N** & **N\({}_{\rm min}\)** \\ \hline TN & 1 & 0.669 \({}^{*}\) & 0.357 & 0.868 \({}^{**}\) & 0.872 \({}^{**}\) & 0.683 \({}^{*}\) & \(-\)0.073 & 0.317 \\ MBN & 1 & 0.395 & 0.5532 & 0.547 & 0.791 \({}^{**}\) & 0.047 & 0.459 \\ DON & & 1 & 0.514 & 0.527 & 0.205 & \(-\)0.701 \({}^{*}\) & \(-\)0.382 \\ PON & & & 1 & 1.000 \({}^{**}\) & 0.658 \({}^{*}\) & \(-\)0.111 & 0.276 \\ ATN & & & & 1 & 0.663 \({}^{*}\) & \(-\)0.121 & 0.272 \\ NO\({}_{3}\)\({}^{-}\)N & & & & & 1 & 0.287 & 0.740 \({}^{**}\) \\ NH\({}_{4}\)\({}^{+}\)-N & & & & & & 1 & 0.857 \({}^{**}\) \\ N\({}_{\rm min}\) & & & & & & 1 \\ \hline \end{tabular} Note: \({}^{**}\) stands for \(p\) < 0.01; \({}^{*}\) stands for \(p\) < 0.05.  
\end{table} 
Table 3: Pearson correlation analysis among soil active nitrogen components. soil nitrogen storage [6]. The soil nitrogen pool is an important indicator of soil health. This study showed that returning organic materials to the field significantly increased the nitrogen content in the soil, which is consistent with the results of previous studies [9; 18]. Organic materials are an important source of soil nitrogen that can reduce the nitrogen deficiency in crops, improve the soil organic carbon pools, and also increase the content of active nitrogen components in the soil [19; 20; 21].