Influence of film color, mulching ratio and soil–mulch contact degree on heat transfer in Northwest China

The impact of diverse mulching factors on crop growth depends on their influences on heat transfer, while the precise effects of these factors on heat transfer remain unclear. To address this knowledge gap, we employed the CropSMPAC model to simulate energy fluxes and soil temperature under varying mulching conditions. Our study integrated a soil column experiment and a three–year field experiment. The soil column experiment encompassed 13 treatments, incorporating 3 plastic film colors, i.e., transparent film (TM), black film (BM), and silver–grey film (GM), and 2 mulching ratios (f_m), i.e., 100 % and 75 %, as well as 2 distances between soil and film (Z_sm), i.e., 0 and 5 mm, along with a control treatment (no mulching). The filed experiment comprised 2 treatments, i.e., film mulching (FM) and no mulching (NM), utilizing TM with a f_m of 97.98 % and Z_sm of 5 mm under FM condition. Results demonstrated the robust performance of the CropSMPAC model in predicting hourly soil surface temperature, hourly soil temperature in the night at 10 cm depth, daily soil water content at 10 cm depth across varying mulching scenarios. Furthermore, the model aptly captured soil temperature, net radiation flux (R_n) and soil heat flux (G) during the maize growth stages under both FM and NM conditions. For daily soil temperature at 10 cm depth, the root mean square error (RMSE) were 1.71 and 2.71 °C, Nash–Sutcliffe efficiency coefficient (NSE) were 0.79 and 0.55, and determination coefficient (R²) were 0.76 and 0.75 for FM and NM, respectively. Corresponding values for daily R_n were 37.3 and 42.7 W m^–2 (RMSE), 0.56 and 0.47 (NSE), and 0.72 and 0.66 (R²), they were 8.5 and 6.9 W m^–2 (RMSE), 0.44 and 0.56 (NSE), and 0.62 and 0.72 (R²) for daily G. Both measurements and simulations revealed that TM increased soil temperature in the daytime and night. In contrast, BM and GM raised soil temperature only in the night. The soil temperature under f_m of 100 % was higher than under f_m of 75 % for both TM and BM. Film mulching with Z_sm of 5 mm contributed to an increase in soil temperature compared with Z_sm of 0 mm for TM, while led to a reduction for BM. Additionally, a dense crop canopy helped mitigate the fluctuations in G and soil temperature, and the warming effect of plastic film mulching also weakened with the increase of canopy coverage.