Accurate measurement of soil NO₃⁻-N is essential for precision fertilization and stable crop yields. Real-time monitoring of NO₃⁻-N has long been a challenge in agriculture. Conventional soil nutrient testing relies on time-consuming laboratory-based chemical analysis. Existing nitrogen monitoring technologies also have limitations regarding in situ deployment, temporal resolution, and continuous tracking. Furthermore, they are susceptible to interference from soil moisture, salinity, and complex field conditions. This makes them inadequate for the high-frequency, large-scale monitoring required by modern precision agriculture.