# Urbanization and Grain Production Pattern of China: Dynamic Effect and Mediating Mechanism
## 4 Results
### Mediating Paths of Urbanization's Effects on the GPP  
A mediating effect model considering the spatial effect was established to identify the mechanism by which urbanization indirectly affected the GPP through cropland utilization, planting structure adjustment, and agricultural technology progress. The identification was performed using the sequential test of mediating effect model [44]. Given that urbanization had more significant effect on the GPCI under W3, the analysis of spatial mediation test results was performed under W3. Table 6 presents the test results of the mediated transmission paths of urbanization's effect on GPP under the grain distance matrix W3. Here, Model 7 shows the aggregate effect of urbanization on the GPCI, consistent with Model 4 (Table 4). Models 8 to 10 show the effect of urbanization on the mediating variables, including MCI, PS, and ATECH, respectively. Models 11 to 13 show the effect of urbanization and mediating variables on \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Variables**} & \multicolumn{2}{c}{**W1**} & \multicolumn{2}{c}{**W3**} & \multicolumn{2}{c}{**Non-Spatial Model**} \\ \cline{2-7}  & **Model 1** & **Model 2** & **Model 3** & **Model 4** & **Model 5** & **Model 6** \\ \hline \multirow{3}{*}{L\_InGPP} & 0.986 *** & 0.954 *** & 0.855 *** & 0.820 *** & 1.013 *** & 1.293 *** \\  & (70.89) & (54.85) & (36.59) & (32.17) & (56.41) & (12.02) \\ \multirow{3}{*}{W*InGPP} & 0.145 *** & 0.172 *** & 0.282 *** & 0.304 *** & - & - \\  & (4.74) & (5.29) & (8.10) & (8.38) & - & - \\  & 0.0004 & \(-\)0.001 & \(-\)0.001 & \(-\)0.003 *** & \(-\)0.001 *** & \(-\)0.0005 \\ \multirow{3}{*}{URBAN} & (0.54) & (\(-\)1.55) & (\(-\)1.48) & (\(-\)3.04) & (\(-\)4.32) & (\(-\)0.46) \\  & \(-\)0.156 *** & 0.435 & \(-\)0.051 * & 0.253 & \(-\)0.049 *** & 0.527 ** \\ \multirow{3}{*}{
\begin{tabular}{c} Control \\ AR (1) P \\ AR (2) P \\ Sargan P \\ Wald P \\ \end{tabular} } & \multicolumn{2}{c}{} & \multicolumn{2}{c}{} & \multicolumn{2}{c}{} & \multicolumn{2}{c}{} & \multicolumn{1}{c}{} \\ \hline \hline \end{tabular} Note: *** \(p<\) 0.01, ** \(p<\) 0.05, * \(p<\) 0.1. Round brackets show \(t\)-values (z-values for non-spatial models).  
\end{table} 
Table 5: Dynamic spatial panel econometric results of urbanization affecting GPP. GPCI. The estimation results showed that the time lag effect and spatial spillover effect remained significant at different stages of the mediating paths. Cropland urbanization, planting structure, and technological progress are all significant transmission mechanisms through which urbanization affects regional GPP. 1. Urbanization significantly affects GPCI through changes in cropland utilization (MCI). The increased level of urbanization significantly reduced the MCI (Model 8), while the increased MCI significantly increased the regional GPCI (Model 11). The negative effect of urbanization considering the MCI (\(-0.0029\)) is lower than the total effect of urbanization (\(-0.003\)). Therefore, the mediating effect of MCI weakens the negative impact of urbanization on GPCI. The mediating effect of cropland utilization is \(-0.219\times 0.001=-0.000219\), accounting for \(7.30\%\) of the total effect, which makes it a partial mediating role. The mediating effect of MCI significantly weakens the negative impact of urbanization on the GPP, exhibiting a transmission path of \" urbanization \(\rightarrow\) cropland utilization \(\rightarrow\) GPP\". Thus, H2 is verified. 2. Urbanization significantly affects GPCI through planting structure adjustments (PS). The increase in urbanization significantly reduced the proportion of grain crops planted (Model 9), while the increase in the proportion of grain crops planted significantly increased the regional GPCI (Model 12). The negative effect of urbanization considering the PS (\(-0.0027\)) is lower than the total effect of urbanization (\(-0.003\)). Therefore, the mediating effect of PS partially offsets the negative impact of urbanization on the GPCI.