## 2 Materials and Methods
### Method of Sampling and Soil Testing  
Soil samples (Nos. 1-12) were, respectively, derived from the 12 broccoli field plots in the Modern Agricultural Distinct of Chongming county in Shanghai, where the core model of the base of 400 ha in total was prevalent. The soil samples were collected after the last crop was harvested with a sampling depth of 20 cm.  
According to the field shape of each plot, soil samples were collected by the \"X\" style mixed random sampling method, and from each sample about 0.5 kg was taken from different field plot points. The samples from different points of each plot were mixed and sampled as 0.5-1.0 kg using the quartering method. The soil samples were spread out on a table; impurities were removed, dried naturally, and crushed; and the soil samples were preserved in jar after being filtered through the 2 mm sieve.  
The potassium dichromate titrimetric method was used to determine the content of the soil organic matter (SOM). The potential method was used to measure the pH of soil. The semi-micro quantitative analysis method was utilized to indicate the total N content in the soil. The conventional alkaline hydrolysis diffusion method was used to determine the available N content. The Mo-Sb anti-spectrophotography method with 0.5 mol/L NaHCO3 was used to indicate the available P content. Flame photometry was employed to determine the available K content [11; 20].  
The results of the soil testing of 12 different field plots (Nos. 1-12) are presented in Table 2.  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Treatment**} & \multicolumn{3}{c}{**Coded Value**} & \multicolumn{3}{c}{**Fertilization Rate (kg/ha)**} & \multirow{2}{*}{**Yield of ZSHL**} & \multirow{2}{*}{**Yield of HL-5**} \\ \cline{2-2} \cline{6-9}  & \(\mathbf{X_{1}}\) & \(\mathbf{X_{2}}\) & \(\mathbf{X_{3}}\) & \(\mathbf{N}\) & \(\mathbf{P_{2}O_{5}}\) & \(\mathbf{K_{2}O}\) & (kg/ha) & (kg/ha) \\ \hline
1 & 0 & 0 & 2 & 225 & 90 & 270 & 12,548.7 & 12,352.3 \\
2 & 0 & 0 & \(-\)2 & 225 & 0 & 0 & 11,365.2 & 13,275.6 \\
3 & \(-\)1.414 & \(-\)1.414 & 1 & 65.925 & 26.37 & 202.5 & 8521.4 & 8606.7 \\
4 & 1.414 & \(-\)1.414 & 1 & 384.08 & 26.37 & 202.5 & 12,654.3 & 16,452.3 \\
5 & \(-\)1.414 & 1.414 & 1 & 65.925 & 153.63 & 202.5 & 8754.3 & 8995.1 \\
6 & 1.414 & 1.414 & 1 & 384.08 & 153.63 & 202.5 & 13,072.6 & 17,258.4 \\
7 & 2 & 0 & \(-\)1 & 450 & 90 & 67.5 & 12,243.5 & 12,952.3 \\
8 & \(-\)2 & 0 & \(-\)1 & 0 & 90 & 67.5 & 5637.3 & 9033.2 \\
9 & 0 & 2 & \(-\)1 & 225 & 180 & 67.5 & 11,434.5 & 11,855.8 \\
10 & 0 & \(-\)2 & \(-\)1 & 225 & 0 & 67.5 & 11,032.1 & 10,942.0 \\
11 & 0 & 0 & 0 & 225 & 90 & 135 & 12,768.9 & 16,973.3 \\ \hline \hline \end{tabular}
\end{table}
Table 1: The yields of broccoli under various fertilization treatments.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Field Code**} & \multicolumn{1}{c}{**Total N**} & \multicolumn{1}{c}{**Available N**} & \multirow{2}{*}{**Available P**} & \multirow{2}{*}{**Available K**} & \multirow{2}{*}{**Organic Matter**} & \multirow{2}{*}{**pH**} \\  & **Content (\%)** & & & & & **Content (mg/kg)** & & **Content (\%)** & \\ \hline
1 & 0.11 & 62.35 & 35.6 & 156 & 1.73 & 7.72 \\
2 & 0.12 & 56.82 & 31.2 & 166 & 1.56 & 7.53 \\
3 & 0.12 & 60.87 & 40.4 & 163 & 1.76 & 7.51 \\ \hline \hline \end{tabular}
\end{table}
Table 2: The results of the soil testing of 12 different field plots.