## 3 Results
### Principal Component Analysis and Correlation Analysis  
Principal component analysis (PCA) allowed for isolating five principal components in accordance with the Jolliffe cut-off value. In accordance with PCA analysis, the observation point made by an interaction of PC1 and PC2 depicts the overall variance described by the five main components. In the PCA analysis of 10 variables (viz., SWC, SOC, TN, TP, NO3-N, NH4+-N, C:N ratio, N:P ratio, C:P ratio, and wheat yield), PC1 and PC2 were extracted with eigenvalues \(>1\), shown in Figure 5, and explained 78.2% of the total variance. However, PC3, PC4, and PC5 do not permit the addition of supplementary information; that is why they are not included. The maximum loadings of PC1 comprise 58.2% of the total variance and in PC2 the higher loadings of 20.0% of the total variance were observed (Figure 5).  
Figure 6 showed that there was a very significant positive correlation between spring wheat yield and SWC, SOC, TN, NH4+-N, and N/P (\(p<0.001\)), which was consistent with [17], and the correlation coefficients were 0.75, 0.86, 0.85, 0.65, and 0.77, respectively. Additionally, there was a significant positive correlation between yield and C/P, with a correlation coefficient of 0.44. Besides, there was a very significant negative correlation between yield and C/N (\(p<0.001\)), and the correlation coefficient was \(-0.75\). Additionally, there was a weak negative correlation with the NO3-N content, which did not reach a significant level, and there was no relationship with TP.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Treatment** & **Plant Height (cm)** & **Grain Number** & **Thousand Grain** & **Biological Yield** & **Grain Yield** \\  & & **Per Spike** & **Weight (g)** & **(kg/ha)** & **(kg/ha)** \\ \hline CT & \(75.97\pm 0.23\)D  & \(29.33\pm 2.03\)D  & \(40.72\pm 1.27\)D  & \(3123.51\pm 142.93\)F  & \(1429.05\pm 38.02\)E  \\ CTN & \(87.27\pm 1.56\)C  & \(33.33\pm 1.76\)CD  & \(44.22\pm 1.35\)CD  & \(3496.80\pm 17.96\)EF  & \(1511.88\pm 35.40\)DE  \\ CTM & \(91.53\pm 2.27\)C  & \(33.67\pm 2.73\)CD  & \(45.74\pm 1.07\)CD  & \(3934.71\pm 194.58\)E  & \(1540.88\pm 47.10\)CD  \\ CTNM & \(105.3\pm 3.19\)B  & \(40.33\pm 3.48\)RC  & \(47.37\pm 2.98\)ARC  & \(4936.08\pm 184.04\)D  & \(1622.51\pm 11.58\)RD  \\ NT & \(102.1\pm 5.95\)B  & \(43.67\pm 1.20\)B  & \(48.69\pm 2.81\)ARC  & \(5264.73\pm 410.50\)CD  & \(1649.12\pm 340.70\)RC  \\ NTN & \(104.8\pm 3.20\)B  & \(45.2\pm 2.08\)AB  & \(49.03\pm 0.45\)ARC  & \(5779.29\pm 25.6\)BC  & \(1703.19\pm 37.17\)B  \\ NTM & \(106\pm 3.57\)B  & \(47.67\pm 2.73\)AB  & \(50.46\pm 1.36\)AB  & \(6296.63\pm 403.60\)B  & \(1744.51\pm 72.10\)AB  \\ NTNM & \(116.2\pm 2.76\)A  & \(51.33\pm 1.76\)A  & \(52.79\pm 0.84\)A  & \(7163.95\pm 112.73\)A  & \(1843.88\pm 34.40\)A  \\ \hline \hline \end{tabular}
\end{table}
Table 6: Effects of tillage and nitrogen fertilization on yield of spring wheat.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Factor** & **Item** & **Yield** \\ \hline  & df & 1 \\ Tillage measure & F & 50.788 \\  & Sig & \(<\)0.01 \\  & df & 3 \\ Fertilization method & F & 7.581 \\  & Sig & \(<\)0.01 \\  & df & 3 \\ Tillage measure and Fertilization method & F & 0.06 \\  & Sig & \(<\)0.01 \\ \hline \hline \end{tabular}  
\(\mathrm{Sig}<0.01\) indicates that the effect is extremely significant.  
\end{table}
Table 7: Two-way factor ANOVA of spring wheat yield under different treatments.  
Figure 5: Principal component analysis of yield, SWC, soil nutrients, and stoichiometric characteristics.  
Figure 6: Correlation heat map of spring wheat yield, soil nutrients, and stoichiometric characteristics. SWC: gravimetric soil water content, SOC: soil organic carbon, TN: total nitrogen, TP: total phosphorus, NO\({}_{3}\) –N: nitrate nitrogen and NH\({}_{4}\)+-N: ammonium nitrogen, C/N: soil carbon and total nitrogen ratio, C/P: soil carbon and total phosphorus ratio and N/P: soil total nitrogen and total phosphorus ratio.