Application of SWAP Model for Modelling a Sugarcane Farming System with Controlled Subsurface Drainage

Realistic agro-hydrological modeling of the sugarcane fields with subsurface drainage in Khuzestan Province, Iran, is a challenging problem, due to rapid fluctuations of the shallow groundwater and, hence, water balance components, and significant size (~ 20 ha) of the fields. In this work, a distributed agro-hydrological modeling scheme was developed through the application of a modified version of the SWAP model and an improved variant of Unified Particle Swarm Optimization (UPSO) algorithm with capability of sub-daily calibration and simulation of controlled drainage. The developed modeling scheme was applied to a sugarcane (CP48-103 cultivar) field with controlled drainage (at 90 cm below ground level) in Imam Khomeini Sugarcane Agro-industrial Company farms, during 2010-2011 (481 days). The results demonstrated the success of the developed modeling scheme in retrieving the measured soil moisture, groundwater level, subsurface drainage outflow (with an EF of 0.829, 0.922, and 0.857 for calibration dataset; and 0.877, 0.781, and 0.712 for validation dataset, respectively), soil water solute concentration, subsurface drainage outflow salinity (with a NRMSE of 0.124 and 0.079 for calibration dataset; and 0.152 and 0.072 for validation dataset, respectively), Leaf Area Index, cane yield, and sucrose yield (with an EF of 0.997, 0.993, and 0.988, respectively). Based on the solute balance components simulated throughout the simulation period, ~ 30.10 ton salt ha-1 was added to the soil due to saline irrigation water, and ~ 45.25 ton salt ha-1 was discharged into the receiving water bodies via surface/subsurface field drains.