## 4 Conclusions  
(1) Taking the Zhongji Miele 1304 cultivating fertilizer applicator as the research object, designing a variable formula fertilization control system composed of pressure sensors, speed sensors, servo motors, vehicle-mounted control terminals, and fertilization \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**No.**} & \multirow{2}{*}{**Fertilizer**} & \multirow{2}{*}{**/kg**} & **Target Cutting** & **Formula** & **Actual Fertilization** & **Target Fertilization** & **Fertilization** \\  & & & **Weight** & **Control Error** & **Weight** & **Weight** & **Control Error** \\  & & & /(kg/mu) & /\% & /kg & /kg & /\% \\ \hline \multirow{3}{*}{1} & N & 2.67 & 2.54 & 4.87 & & & \\  & P & 9.33 & 9.46 & 1.39 & 16.85 & 16.67 & 1.08 \\  & K & 4.67 & 4.80 & 2.78 & & & \\ \hline \multirow{3}{*}{2} & N & 2.00 & 2.08 & 4.00 & & & \\  & P & 9.47 & 9.65 & 1.87 & 17.56 & 17.07 & 2.79 \\  & K & 5.60 & 5.48 & 2.14 & & & \\ \hline \multirow{3}{*}{3} & N & 2.33 & 2.25 & 3.43 & & & \\  & P & 9.13 & 9.02 & 1.20 & 16.88 & 17.19 & 1.84 \\ \cline{1-1}  & K & 5.73 & 5.85 & 2.09 & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Test to verify measurement results. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**No.**} & \multirow{2}{*}{**Target Fertilization**} & \multirow{2}{*}{**Traditional Uniform**} & **Variable Formula** & **Difference between Traditional and Variable Fertilization** \\  & & & /(kg/mu) & /(kg/mu) & /(kg/mu) \\ \hline
1 & 16.67 & 17.69 & 16.77 & 0.92 \\ \hline
2 & 17.07 & 18.23 & 16.59 & 1.64 \\ \hline
3 & 17.19 & 17.86 & 16.99 & 0.87 \\ \hline \multicolumn{4}{c}{Average value} & 1.14 \\ \hline \hline \end{tabular} Note: Mu is a unit of land area under the municipal system in China, equal to about 666.7 square meters. A hectare is equal to about 15 mu.  
\end{table} 
Table 5: Test to verify measurement results. actuators with PLC controller as the core. Based on pre-loaded soil prescription diagram and combining fertilizer pressure and ground wheel speed detection information, the system obtained a formula fertilization control strategy through calculation to realize the rapid and automatic formula of nitrogen, phosphorus, and potassium fertilizers and the precise variable fertilization. (2) The experiment researched the performance of the variable formula fertilization control system, carried out pressure sensor calibration, fertilizer discharge measurement, and speed sensor test. The results showed that the error range of the pressure sensor measurement value was 0.005-0.03%, which satisfied weighing measurement accuracy requirements; in the controller, three gears of low, medium, and high were set up for the motor speed, corresponding to the motor speed of 10, 30, and 50 r/min, respectively. Then, the corresponding calibration data nitrogen (N) average fertilizer outputs were 52.4, 46.9, and 41.8 g/r, and the standard deviations were 1.3, 2.8, and 1.2 respectively; phosphorus (P) average fertilizer outputs were 64.3, 60.3, and 55.8 g/r, and the standard deviations were 2.9, 3.1, and 0.8, respectively; potassium (K) average fertilizer outputs were 86.0, 82.7, and 79.4 g/r, and the standard deviations were 1.0, 4.3, and 1.1, respectively; the measurement accuracy of the speed sensor was above 98%, which met the requirements of the variable formula fertilization test speed test. (3) In the process of experimental verification, the formula control error was less than 5%, and the fertilizer control error was 1.08%, 2.79%, 1.84%, respectively. The control accuracy of the variable formula fertilization system had reached more than 95%, which met the requirements of variable formula and precise fertilization. In addition, compared with the traditional uniform fertilization operation, this variable formula fertilization control system saved an average of 1.14 kg of chemical fertilizer per mu (that was to save 17 kg per hectare). It could effectively save chemical fertilizers and reduce operating costs and had good economic benefits.