## 3 Results
### The Application of Formula Fertilization Models
#### 3.3.2 Recommended Amounts of N, P, and K Fertilizers in 12 Different Field Plots  
According to Equation (13), combined with the nutrient contents of soil samples (Table 2), the recommend amounts of N, P, and K fertilizers in 12 different field plots were calculated according to the maximum yield target of the early-maturing variety, ZSHL. The recommended amounts of N, P, and K fertilizers in different plots are summarized in Table 3.  
The recommended amounts of fertilizers were different in plots of different soil nutrient levels. The recommended amounts of N were 338.36-514.65 kg/ha under different soil N levels, and the maximum recommended amount of N was elevated by 52.10% compared with the minimum recommended amount of N. The recommended amounts of P were 52.81-125.45 kg/ha in different soil P levels, and the maximum recommended amount of P was increased by 137.55% compared with the minimum recommended amount of P. The recommended amounts of K were 146.12-242.92 kg/ha in different soil K levels, and the maximum recommended amount of K was elevated by 66.25% compared with the minimum recommended amount of K.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & & & & & & \\ \cline{2-6} \multirow{2}{*}{**Field Plot**} & \multicolumn{2}{c}{**N**} & \multicolumn{2}{c}{**P\({}_{2}\)O\({}_{5}\)**} & \multicolumn{2}{c}{**K\({}_{2}\)O**} \\  & **kg/ha** & & **kg/ha** & & **kg/ha** \\ \cline{2-6} \multirow{2}{*}{} & **ZSHL** & **HL-5** & **ZSHL** & **HL-5** & **ZSHL** & **HL-5** \\ \hline
1 & 367.67 & 407.83 & 67.84 & 57.24 & 242.92 & 258.46 \\
2 & 423.77 & 472.74 & 81.62 & 73.19 & 208.35 & 218.45 \\
3 & 382.69 & 425.20 & 52.81 & 39.85 & 218.72 & 230.45 \\
4 & 379.14 & 421.09 & 77.24 & 68.11 & 180.69 & 186.43 \\
5 & 338.36 & 373.90 & 104.79 & 100.00 & 156.49 & 158.42 \\
6 & 514.65 & 577.93 & 107.61 & 103.26 & 177.23 & 182.43 \\
7 & 359.76 & 398.67 & 100.09 & 94.57 & 187.61 & 194.44 \\
8 & 417.98 & 466.05 & 112.30 & 108.70 & 146.12 & 146.42 \\
9 & 378.83 & 420.74 & 118.56 & 115.95 & 208.35 & 218.45 \\
10 & 358.85 & 397.61 & 112.30 & 108.70 & 184.15 & 190.44 \\
11 & 364.53 & 404.19 & 125.45 & 123.92 & 239.47 & 254.46 \\
12 & 382.58 & 425.08 & 121.07 & 118.84 & 211.81 & 222.45 \\ \hline \hline \end{tabular}
\end{table}
Table 3: The recommended amounts of N, P, and K fertilizers in different field plots.  
For late-maturing variety HL-5, according to the Equation (13) and the response function with the maximum yield, combined with the nutrient contents of soil samples (Table 2), the recommended amounts of N, P, K fertilizers that produce the maximum yield could be calculated. The recommended amounts of N were 373.93-577.93 kg/ha in different soil N levels, and the maximum recommended amount of N was increased by 54.56% compared with the minimum recommended amount of N. The recommended amounts of P were 39.85-123.92 kg/ha in different soil P levels, and the maximum recommended amount of P was increased by 210.97% compared with the minimum recommended amount of P. The recommended amounts of K were 146.42-258.46 kg/ha in different soil K levels, and the maximum recommended amount of K was elevated by 76.52% compared with the minimum recommended amount of K.