Optimal control for precision irrigation of a large-scale plantation

Reference:
R.C. Kassing, B. De Schutter, and E. Abraham, "Optimal control for precision irrigation of a large-scale plantation," Water Resources Research, vol. 56, no. 10, Oct. 2020. Article e2019WR026989.

Abstract:
Distributing water optimally is a complex problem that many farmers face yearly, especially in times of drought. In this work, we propose optimization-based feedback control to improve crop yield and water productivity in agriculture irrigation for a plantation consisting of multiple fields. The interaction between soil, water, crop (sugarcane in this work), and the atmosphere is characterized by an agro-hydrological model using the crop water productivity modeling software AquaCrop-OS. To optimally distribute water over the fields, we propose a two-level optimal control approach. In this approach, the seasonal irrigation planner determines the optimal allocation of water over the fields for the entire growth season to maximize the crop yield, by considering an approximation of the crop productivity function. In addition, the model predictive controller takes care of the daily regulation of the soil moisture, respecting the water distribution decided on by the seasonal planner. To reduce the computational complexity of the daily controller, a mixed-logic dynamical model is identified based on the AquaCrop-OS model. This dynamical model incorporates saturation dynamics explicitly to improve model quality. To further improve performance, we create an evapotranspiration model by considering the expected development of the crop over the season using remote-sensing-based measurements of the canopy cover. The performance of the two-level approach is evaluated through a closed-loop simulation in AquaCrop-OS of a real sugarcane plantation in Mozambique. Our optimal control approach boosts water productivity by up to 30% compared to local heuristics and can respect water use constraints that arise in times of drought.