Plastic film mulching (FM) has been widely used to increase wheat yield in arid and semiarid regions. However, most researchers have focused on FM during the growth period of winter wheat; as such, a knowledge gap remains regarding FM in other periods. Accordingly, we established a long-term field experiment in 2002 that included four treatments on the Loess Plateau of China. These four treatments included the following: regular fertilization without film (NP), regular fertilization with FM in the fallow period (NPFF), regular fertilization with FM in the growth period (NPFG), regular fertilization with FM for the whole year (NPFW). In 2020 - 2021, we measured the soil water distribution and root distribution in the 0 - 200 cm profile; the soil temperature in 5, 15, 30, and 50 cm soil layers; the winter wheat grain yield; the water use efficiency (WUE); and rainfall use efficiency (RUE). Our results demonstrated that compared with NP, the winter wheat yield of NPFF, NPFG, and NPFW improved by 37.1%, 7.8%, and 21.3% (p < 0.05). The WUE of NPFF, NPFG, and NPFW was 29.5%, 14.3%, and 12.5% higher than NP. Additionally, the RUE of NPFF, NPFG, and NPFW was 37.8%, 8.9%, and 22.2% higher than NP. The profile's annual average soil temperature of NPFF, NPFG, and NPFW were 0.6 degrees C, 1.0 degrees C, and 1.4 degrees C higher than NP. Further, the root mass of NPFF, NPFG, and NPFW were 16.7%, 41.7%, and 8.3% higher than NP, respectively, and the root mass percentage of NPFF, NPFG, and NPFW decreased significantly by 7.3%, 6.0%, and 24.8% less than NP, respectively, in the 0 - 40 cm soil layer (p < 0.05). In sum, FM during the fallow period was considered an appropriate yield increase measure on the Loess Plateau of China and similar regions because of its advantages in collecting precipitation during the fallow period, regulating wheat growth temperature, and obtaining high yields.
