Coupled simulation of soil water flow, solute transport and crop growth processes at field scale and its validation

The quantitative description of soil water flow, solute transport and crop growth processes at field scale is significant for the decision-making of appropriate water use practices in arid irrigation districts. In this study, a modified agro-hydrological model (SWAP-EPIC) for coupled simulation of soil water flow, solute transport and crop growth was developed based on SWAP (soil water atmosphere plant) model and EPIC (environmental policy integrated calculator) crop growth model. The variable active-node method was adopted into the original SWAP model for reasonably simulating the soil water and solute transport processes during soil thawing period. Additionally, the S-shaped osmotic head-dependent functions for describing water and salt stress were also introduced. Further, the EPIC crop growth model, which could simulate the crop growth process and actual crop yield with moderate data input and parameters, was coupled into the SWAP model. Then the field applicability of SWAP-EPIC model was respectively tested using the field experiment data of spring wheat and spring maize at Huinong experimental site in Ningxia. The simulated and observed soil moisture, salinity concentration, and crop growth indicator (leaf area index and dry above-ground biomass) were compared for spring wheat and spring maize. The results showed that the soil moisture was matched very well, with MRE (mean relative error) and RMSE (root mean square error) close to zero and NSE (NSE and Sutcliffe model efficiency) approached to one. The simulated and observed salinity concentration showed an agreement with some slight discrepancy. The simulated LAI and above-ground biomass both matched well with observed ones. Meanwhile, the simulated crop yield was also close to the observations, with relative errors of 4.9% for spring wheat, and 3.3% for spring maize. The results indicated that the modified model (SWAP-EPIC) could be efficiently used to simulate the soil water and salt dynamics, crop growth, and their relationships at field scale.