Optimizing drain depth and spacing to minimize nitrogen loss in southwest Punjab using DRAINMOD-NII

Abstract

The DRAINMOD-NII model was used to evaluate the water table behavior and nitrate movement using field data from the Thehri experimental field in Muktsar district, southwest Punjab, India. To optimize the drainage design parameters for efficient nitrogen management, a scenario analysis of water table depth, drain outflows, and nitrogen load was carried out for different drain depths and spacings. The rice–wheat cropping system was followed for 2 years, from 2018 to 2020. The conventional subsurface drainage system was installed in the study area. The recorded data consisted of daily drain outflows, water table depths, daily nitrate concentrations in the drain outflows, and relative crop yields. The DRAINMOD-NII model was calibrated and validated for 2018–2019 and 2019–2020, respectively. The model's reliability was assessed by comparing the measured and predicted values of daily drain outflows, water table depth, daily nitrate loads, and relative crop yields during each season. A better agreement was found between the observed and simulated values. Root mean square error, Nash–Sutcliffe model efficiency, R², and percentage bias values during the calibration period ranged from 1.76 to 7.5; 0.48 to 0.88; 0.70 to 1.00; and −6.04 to 5.02, respectively, for the recorded parameters. A similar statistical evaluation was also performed during the validation period. The scenario analysis of drain depth and spacing concluded that a depth of 1.3 m and spacing of 42 m could be optimal for better crop yield and lesser nitrogen losses. Hence DRAINMOD NII model is a tool for drainage systems design.