## 3 Results and Discussion
### Experimental Validation
At the highest target EC of 2.2 mS/cm, the steady-state EC ranged from 2.12 to 2.28 mS/cm, the steady-state time was 130 s, and the overshoot was 17.2%. The VSMC method demonstrated the best overall performance among the three control algorithms. At a target EC of 1.4 mS/cm, the system reached a steady-state EC range from 1.18 to 1.60 mS/cm, with a steady-state time of 95 s and an overshoot of 14.3%. For a target EC of 1.8 mS/cm, the steady-state EC varied from 1.60 to 1.98 mS/cm, with a steady-state time of 100 s and an overshoot of 15.5%. At the highest target EC of 2.2 mS/cm, the steady-state EC ranged from 2.06 to 2.35 mS/cm, with a steady-state time of 120 s and an overshoot of 16.1%. Analyzing the results, it is evident that the VSMC method outperformed both the PI and SMC methods in terms of response speed, steady-state time, and overshoot across all tested target EC values. The improved performance of the VSMC method can be attributed to its ability to dynamically adjust the sliding mode surface parameters based on observed values of rotational inertia and load torque. This adaptive capability allows the VSMC method to handle disturbances and changes in system parameters more effectively, leading to more accurate and stable control. The field experiments further validate these findings, demonstrating that the VSMC method consistently achieved faster steady-state times, lower overshoot percentages, and smaller EC fluctuation ranges. This enhanced performance is particularly significant  
Figure 16: The control performance of the sliding mode control (SMC) method. Figure 17: The control performance of the variable-parameter sliding mode control (VSMC) method. for practical agricultural applications, where the precise and stable control of water and fertilizer integration is crucial for optimizing crop yields and conserving resources. The superior performance of the VSMC method highlights its potential as a robust and efficient solution for managing the dynamic and nonlinear characteristics inherent in water and fertilizer integration systems. Its ability to achieve rapid convergence to set points, minimal overshoot, and effective disturbance rejection makes it an ideal choice for improving the efficiency and effectiveness of agricultural irrigation and fertilization processes. To further validate the effectiveness of the VSMC method in regional irrigation applications, a comparative experiment was conducted between the conventional PI control method and the proposed VSMC-based remote conductivity method. The experiments were performed on the same plot, with a one-month interval between two operations. To minimize external disturbances, artificial irrigation and natural rainfall were avoided for three days prior to each trial. The experimental field was divided into 45 subplots, labeled using a combination of letters (A-E) and numbers (1-9). The deviations between the target and actual applied potassium nitrate fertilizer content across different regions were analyzed (as shown in Figure 18). The distribution of soil potassium nitrate fertilizer content before and after irrigation was compared to assess the performance of both methods in controlling irrigation uniformity. As illustrated in Figures 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17 and 18a, the conventional PI control method exhibited the largest over-application in subplot B8, where 7.48 kg/ha of excess potassium nitrate was applied. The most under-applied region was B2, with a deficit of 6.52 kg/ha. The overall standard deviation of the PI control method was 2.14. In contrast, as shown in Figures 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17 and 18b, the VSMC method exhibited a significantly improved uniformity. The largest over-application occurred in subplot C4, with an excess of 1.06 kg/ha, while the most under-applied region was A4, with a deficit of 2.01 kg/ha. The overall standard deviation of the VSMC method was reduced to 0.59, demonstrating its superior precision in achieving the desired fertilizer distribution.