## 3 Results and Discussion
### The Decadal Changes of Heavy Metals and Relations with Industrial Producing  
The mean value of pH in cinnamon soil and fluvo-aquic soil in 2017 was relatively higher than that in 2007, which suggested that yearly farming changed soil physical feature and grain yield, as pH was significantly and positively correlated with crop production (46). The concentrations of Cu, Pb, \begin{table}
\begin{tabular}{c c c c c c c c} \hline Soil types (2017) & Cu & Pb & Cd & Cr & Ni & Zn & pH \\ \hline Brown soil & 24.06 & 32.2 & 0.38 & 152.76 & 20.02 & 65.66 & 6.47 \\ Cinnamon soil & 26.39 & 33.21 & 0.25 & 150.2 & 24.12 & 80.65 & 6.98 \\ Fluvo-aquic soil & 22.36 & 28.04 & 0.14 & 80.64 & 21.36 & 68.43 & 8.10 \\ \hline Soil types (2007) & Cu & Pb & Cd & Cr & Ni & Zn & pH \\ \hline Brown soil & 73.87 & 99.05 & 0.08 & — & — & 85.93 & 6.70 \\ Cinnamon soil & 62.81 & 130.21 & 0.32 & — & — & 143.12 & 6.78 \\ Fluvo-aquic soil & 62.53 & 140.76 & 0.26 & — & — & 141.63 & 7.82 \\ \hline \end{tabular}
\end{table} 
Table 2: The concentrations of heavy metals in 2007 and 2017 (mg-kg\({}^{-1}\)) (5). \begin{table}
\begin{tabular}{c c c c c c c} \hline
**Parameters** & **Cr** & **Ni** & **Cu** & **Zn** & **Cd** & **Pb** \\ \hline Cr & 1 & & & & & \\ Ni & \(-0.005\) & 1 & & & & \\ Cu & 0.104 & **0.313** * & 1 & & & \\ Zn & **0.280** * & **0.292** * & **0.530** & 1 & & \\ Cd & 0.058 & **0.320** * & 0.033 & 0.248 & 1 & \\ Pb & 0.099 & 0.226 & \(-0.016\) & 0.165 & **0.788** & 1 \\ Gross product & 0.15 & \(-0.055\) & \(-0.114\) & **-0.284** * & \(-0.01\) & 0.034 \\ The primary industrial & & & & & \\ added value & 0.048 & \(-0.199\) & \(-0.187\) & **-0.307** * & 0.001 & \(-0.08\) \\ The secondary industrial & & & & & \\ added value & & & & & \\ The industrial added value & & & & & \\ The tertiary industrial & & & & & \\ added value & & & & & \\ \hline \end{tabular}
\end{table} 
Table 3: The Pearson correlation analysis of heavy metals and economic indicators. Zn and Cd in 2017 were significantly decreased with respect to the accumulation in 2007, except for the insignificant change of Cd in brown soils (Table 2); the changes of Cd may attributable to the continuous input, leaching, migration and accumulation procedure of Cd in agricultural soils [19; 44]. The significant reduction of above-mentioned metals from 2007 to 2017 suggests decreased human input, such as by decreasing the utilization of agrochemicals and the discharge of industrial waste and increasing the metal remediation and soil management [47; 48]. Therefore, environmental management and ecological protection is vitally imperative for heavy metal remediation in agricultural soils. The development of industry, agriculture, tourism and services brings about rapid growth of economy and living standards [49; 50]. Meanwhile, the damage to ecological environment is also profound and lasting, which includes soil contamination around the industries, reduction of grain yield, destruction of natural habitat, etc. [51; 52]. Thus, the relationship between economic indicators and heavy metals in agricultural soils should be researched. Factor analysis of heavy metals and economic indicators indicated three dominant factors, which explained 38.04%, 22.54% and 20.97% of the total factors, respectively (Table 4). The first factor mainly explained the Cd, Pb and all economic indicators, indicating the close relation among Cd, Pb and economic production. Factor 2 explained Cr, Ni, Zn and Cu, which may suggest their common sources. Factor three explained the Cr and primary industrial added value, which indicated a certain industrial input. The remarkable impacts of economic production on Cd and Pb are in accordance with many previous studies [53; 54]. In addition, concentrations of heavy metals presented certain relations with some economic indicators. Specifically, the primary industrial added value showed a significant and negative correlation with concentration of Zn, while industrial added values indicated a significant and positive relationship with the contents of Cd (Table 3).