Evaluating soil water dynamics under a no-tillage system with residual plastic film mulching in an arid region of western China using HYDRUS-2D

No-tillage (NT) with residual plastic film mulching from an earlier year (NTR) is considered an excellent agricultural strategy in arid regions, recommended to reduce not only soil disturbance but also plastic film residues. However, the soil water dynamic in the root zone under this management is more complex due to variations in soil properties and upper boundary conditions. Soil compaction and a disintegrated fraction (DF) of the residual plastic film increase in NTR years. Soil water movement under NTR is not fully understood. It is also necessary to determine a suitable number of NTR years and optimize irrigation to increase water use efficiency (WUE) and maintain sustainable agricultural development. Therefore, the HYDRUS-2D model was calibrated and validated using experimental data from 2019 to 2021 collected in the corn field with conventional tillage (CTN), NT with a new plastic film (NTN), and NTR. The soil water contents (SWC), cumulative water fluxes (CWF), and soil water balances under CTNH, NTNH, and NTRH with the high (subscript H) irrigation depth of 315 mm (the local recommendation) were evaluated using both measured and simulated data. The results for NTRH, NTRM (a medium irrigation depth of 252 mm, 80% of local recommendation), and NTRL (a low irrigation depth of 189 mm, 60% of local recommendation) scenarios were compared, and a suitable number of NTR years was determined. The results of numerical simulations agreed with observations, with the mean relative error range for the calibration and validation periods between 4.9% and 5.4%. The larger number of experimental NTR years, the larger the SWC differences for all irrigation depths, tillage practices, and mulching due to larger soil compaction under NT and a higher DF of the residual plastic film. The largest SWC differences occurred in the 0-30 cm soil layer in the third experimental year (2021), with an average SWC decrease of 2.3% for NTNH compared to CTNH and 10.2% for NTRH compared to NTNH. Simulated two-dimensional SWC distributions further confirmed these experimental results. There were lower CWF under NT and new film mulching. CWF at a depth of 30 cm was 8.5 mm lower for NTNH than for CTNH in 2021. There was a 4.2%, 30.1%, and 43.1% increase in CWF for NTRH compared to NTNH due to higher soil evaporation evaluated from the soil water balance in 2019, 2020, and 2021, respectively. The scenario simulation results showed that SWCs decreased linearly with an increase in DF and that DF of 30% can be regarded as the maximum value for obtaining high WUE under NTR. The highest WUE of 28.3 kg ha(-1) mm(-1) under NTR during two years was found when the local recommended irrigation depth was reduced by 20% (to 252 mm). Therefore, this management can be recommended in arid regions to avoid plastic pollution with higher WUE.