Numerical Simulation of Soil Water–Salt Dynamics and Agricultural Production in Reclaiming Coastal Areas Using Subsurface Pipe Drainage

Abstract

Soil salinization induced by shallow saline groundwater in coastal areas can be managed using subsurface pipe drainage (SPD) for agricultural land reclamation. However, a reasonable SPD system layout should comprehensively consider local hydrological conditions and crop physiological characteristics based on long-term model evaluations. The objectives of this study were to test the applicability of a crop growth model (AquaCrop) for simulating winter wheat growth in SPD-applied fields by employing the water table behaviors predicted by the soil hydrologic model HYDRUS. Model calibration and validation based on field observations suggested that HYDRUS accurately predicted the distributions of soil water–salt dynamics, and the seasonal variations of canopy cover and biomass production predicted by AquaCrop were close to the measured values. The simulation scenarios considering the long-term effect of groundwater salinity (10.53, 21.06, and 31.59 g L−1 for low, medium, and high levels), drain spacing (10, 20, 30, 40 m, and no-SPD), and precipitation category (dry, normal, and wet year) on soil solute transport, grain yield (GY), water productivity (WP), and groundwater supply (GS) were further explored using a combination of HYDRUS and AquaCrop. The simulation results indicated that narrowing the drain spacing could improve the desalination performance of SPD, but there was no continuous downward trend of soil solute concentration during the long-term application of SPD when groundwater salinity was constant. The SPD application could improve grain yield by 0.81–1.65 t ha−1, water productivity by 0.13–0.35 kg m−3, and groundwater supply by 6.06–31.03 mm compared to the no-SPD scenarios, but such increases would be less pronounced in dry years with groundwater salinity at the low level. This study demonstrated that the co-application of hydrologic and crop growth models is a feasible method for revealing the effects of SPD on agricultural land reclamation in coastal areas.