Optimized Farmland Mulching Improves Rainfed Maize Productivity by Regulating Soil Temperature and Phenology on the Loess Plateau in China

Owing to global warming, continuously increasing the grain yield of rainfed maize is challenging on the Loess Plateau in China. Plastic film mulching has been extensively utilized in dryland agriculture on the Loess Plateau. However, higher topsoil temperatures under film mulch caused rainfed-maize premature senescence and yield loss. Here, we aimed to explore the influence of topsoil temperature driven by novel double mulching patterns on rainfed maize productivity based on the excellent moisture conservation function of plastic film. A maize field experiment was conducted in two different areas, namely Changwu, a typical semi-arid area, and Yangling, a dry semi-humid area. The experiment followed a randomized block design with three replications. Five flat-planting practices were examined in 2021 and 2022: (1) bare land (CK), (2) transparent film mulching (PFM), (3) black film mulching (BFM), (4) double mulching of PFM with a black polyethylene net (PFM + BN), and (5) double mulching of PFM with whole maize stalks (PFM + ST). Soil hydrothermal conditions, maize growth dynamics, grain yield, water use efficiency (WUE), and economic returns were quantified under different mulching practices. Under double mulching treatments, topsoil temperatures were lower than PFM by 1.7–2.0 °C at the two sites (<i>p</i> < 0.05), whereas BFM was slightly lower than that of PFM by 0.6–0.7 °C at Yangling (<i>p</i> > 0.05). The average growth period for maize under double mulching was longer than that under PFM by 8–11 days at the two sites. Double mulching treatments significantly improved the leaf area index (LAI), chlorophyll relative content (SPAD), and aboveground biomass compared to CK and PFM during the late growth stage. Compared with PFM, average grain yield increased by 14.93%, 18.46%, and 16.45% in Changwu (<i>p</i> < 0.05) under BFM, PFM + BN, and PFM + ST, respectively, and by 2.71%, 24.55%, and 20.38% in Yangling. The corresponding WUEs also increased. Additionally, net income under BFM was higher than that under other treatments, and there were no significant (<i>p</i> > 0.05) differences between PFM + ST and BFM in Changwu. However, PFM + ST in net income averaged 10.72–52.22% higher than other treatments, and its output value was 19.51% higher in Yangling. In summary, smallholder farmers can adopt PFM + ST to improve rainfed-maize productivity in the Loess Plateau in China.