Simulating Soil Surface Temperature under Plastic Film Mulching During Seedling Emergence of Spring Maize with the RZ–SHAW and DNDC Models

Plastic film mulching has been widely used to increase soil temperature in areas with a cold spring. Reliable simulation of mulched soil surface temperature is important for initial growth of spring crops. The hybrid Root Zone Water Quality-Simultaneous Heat and Water (RZ-SHAW) model and the Denitrification-Decomposition (DNDC) model use different approaches to quantify the effect of plastic film mulching on soil temperature. A two-year field study was conducted to compare the performance of the RZ-SHAW model and DNDC model for simulating the 5-cm soil temperature (T-5) under varying plastic film mulching coverages during seedling emergence of spring maize. Three treatments were used in this study: no mulching (PMO), full plastic film mulch (PM100), and partial plastic film mulch with 60 % coverage, i.e. 60 cm width of plastic every meter (PM60). Compared with no mulching, PM100 and PM60 treatments enhanced daily maximum and average T-5 (2.53 degrees C and 1.25 degrees C, respectively; p < 0.05) while not affecting the diurnal sinusoidal phase change of T-5 (2.45 degrees C and 1.21 degrees C, respectively; p < 0.05). The RZ-SHAW model was robust for T-5 simulation under mulching condition with RMSE and NSE ranged from 2.01 degrees C to 2.51 degrees C and 0.68 to 0.84, respectively, while the DNDC model failed to predict T-5 for mulched soil with RMSE and NSE ranged from 2.79 degrees C to 4.33 degrees C and 0.25 to 0.46, respectively. Employing T-ms (air temperature between plastic film and soil surface) to replace soil surface temperature may be one reason for the poor T-5 simulation of DNDC in mulched plots. By contrast, the RZ-SHAW model ran a complete calculation for heat and vapour transfer within the mulched layer, which robustly simulated atmosphere-soil surface temperature gradient in the plant canopy, surface covering, and soil surface in a broader range of climatic conditions. Additionally, the longwave radiation reflected back to the soil surface by the plastic, which was not considered by DNDC model, was important and enhanced T-5 simulation performance for RZ-SHAW under mulching condition. It suggested to imbed the SHAW module into DNDC for a sufficiently precise simulation of soil temperature and gas emission.