Modelling the effects of plastic mulch on water, heat and CO2 fluxes over cropland in an arid region

Abstract

Plastic mulches are often used to improve agricultural production by suppressing soil evaporation in the vast arid and semi-arid regions. As a special surface cover, plastic mulch evidently affects the surface albedo and prevents vapour exchange between the land surface and the atmosphere, but these physical processes were not contained in the present land surface models. Therefore, simulations remarkably deviate from observations when land surface models are applied to areas with underlying plastic mulch covering. Investigating the effects of various plastic mulches assists in better understanding the atmosphere-land interaction. In this study, a detailed plastic mulch layer model, which considers the effect of plastic mulch on the radiation and heat transfer is constructed and incorporated into a land surface model Two-Big-Leaf-SHAW (TBLSHAW) to simulate the water (H2O), heat and CO2 (carbon dioxide) fluxes in an agro-ecosystem covered by plastic mulch. Data collected by Gulang Heterogeneous Underlying Surface Layer Experiment (GHUSLE) at a plastic mulch-covered cropland site in an arid region were employed to verify the model; simultaneously, the TBLSHAW model was run with the same atmospheric forcing as a comparison to investigate the effect of the plastic mulch. Results suggest that the model can appropriately simulate the water, heat and CO2 fluxes over an arid cropland. The model efficiency is high, and the mean bias error and root mean bias error between the simulated and the observed values are minor. Compared to TBLSHAW simulations, the plastic mulch with special optical properties obviously influenced the surface albedo and radiation balance. By limiting the underside soil evaporation, plastic mulch changes the energy and water transfer between the atmosphere and the land surface. The soil temperature and soil moisture are improved by the transparent plastic mulch, and the plastic mulch not only suppresses the CO2 generated by soil respiration but also affects CO2 budget as a result of the net assimilation controlled by the soil water and heat conditions.