Evaluating the effects of biodegradable film mulching on soil water dynamics in a drip-irrigated field

Drip irrigation with plastic film mulching (PM) is an important agricultural practice used to conserve soil water and produce higher crop yields worldwide. However, the plastic film is usually made from non-degradable polyethylene materials, which may lead to the incorporation of plastic into soils and cause a series of negative environmental effects. As such, biodegradable film mulching (BM) can represent a valuable alternative to PM. A two-year experiment was carried out during the 2014 and 2015 seasons to evaluate the effects of PM, BM, and no film mulching (NM) on the soil water balance in the corn field. The two-dimensional numerical HYDRUS-2D model was calibrated and validated using experimental data collected in 2014 and 2015, respectively, under BM, PM, and NM and then used to evaluate soil water contents (SWC), water fluxes, and soil water balances in two-dimensional soil profiles. The results of numerical simulations were in good agreement with measurements, with the mean relative errors for the calibration and validation periods for BM, PM and NM of 11.2%, 10.7%, and 11.7%, respectively. The results showed that SWCs were similar in the BM and PM scenarios during early and middle crop growth periods. Significant differences in SWCs were observed only after the average fraction of the disintegrated area of the biodegradable film was equal or higher than about 40% (during the late crop growth period). The results also showed that mulching mainly affects SWCs in the top 0-20 cm soil layer. There were significant differences in cumulative evaporation and water fluxes between different treatments, but an insignificant difference in root water uptake between PM and BM. Cumulative evaporation for BM increased by 30.5% compared to PM and decreased by 41.9% compared to NM. Corresponding cumulative water fluxes at the 80 cm depth increased and decreased by 6.6% and 48.8%, respectively. Two-dimensional simulations of soil water content distributions revealed that the "water stress" area in the soil profile (with SWCs lower than readily available water) before irrigation was 1.79 and 0.75 times larger for BM than for PM and NM, respectively. SWCs in the surface soil layer of BM also increased after rainfall during the late crop growth period, which improved the rainwater use efficiency by 8.2% compared to PM. Both experiments and simulations revealed that BM has more comparable soil moisture dynamics to PM than to NM.