Theory and Application of Adaptive Control Systems for Precision Irrigation Under Dynamic Field Conditions in Nigeria

This study develops and applies an adaptive control theory framework for precision irrigation management under dynamic and uncertain field conditions characteristic of Nigerian small-scale farming contexts. Precision irrigation management requires control systems that can maintain optimal crop water status despite highly variable soil properties, weather disturbances, irrigation system performance variations, and sensor measurement uncertainties. Classical control approaches based on fixed set points and proportional-integral-derivative controllers perform inadequately under this level of variability. This study develops an adaptive model predictive control framework for irrigation management that incorporates online soil moisture model parameter updating, stochastic weather forecasting from numerical weather prediction data, and multi-variable optimisation of irrigation timing and volume. The theoretical framework is based on Lyapunov stability analysis and input-to-state stability results adapted for the specific constraints of agricultural control applications. Experimental validation is conducted through a sensor-actuated irrigation control system deployed on four commercial vegetable farms in Ogun and Niger States over three seasons. The adaptive MPC system is compared against static MPC, threshold-based, and farmer calendar-based irrigation control approaches. Findings establish that the adaptive MPC achieves the highest water productivity across all farm sites, reducing irrigation water application by 28 percent compared to farmer practice while maintaining equivalent yields. The system self-corrects for soil property spatial variability within 3 to 5 irrigation cycles. The study contributes an original adaptive control theory for agricultural irrigation and recommends embedded system implementation of the control algorithm for commercial deployment.

Keywords: adaptive control, model predictive control, precision irrigation, Nigeria, soil moisture.