Soil temperature modeling in topsoil with plastic film mulching and low spring temperatures

Mulching has been widely used to increase soil temperature and promote seedling emergence in areas with cold springs. However, soil temperature regulation with mulching is not well controlled, which often leads to failure in crop establishment. A two-year field study was conducted to determine and simulate the effect of transparent plastic film mulching on soil temperatures at 5 cm depth (T-5) using the Denitrification-Decomposition (DNDC) model in the cold Hetao Irrigation District in north-western China. Four treatments were used: no mulch (CK), full mulching with plastic film at 140 cm width (PMF), and partial plastic film mulching at 60 cm width (PM60) and 30 cm width (PM30). Mulching did not result in a sinusoidal phase change in diurnal air temperature (T-a) between mulch and the soil surface (T-ms). T-ms decreased with a decrease in film width. Values of the daily averaged T-ms and T-5 were significantly correlated (R-2 > 0.70). Simulated T-5 matched the observed T-5 well, with marginal overestimation in both no-mulch and mulch conditions (NSE > 0.7). Embedding a simple empirical approach for T-ms calculation can reduce parameter input into the DNDC model, and result in acceptable T-5 simulation.