Rain-fed maize production in semi-arid areas of the Loess Plateau in China is constrained by low temperatures and water limitations during the early growth stage. Traditionally, gravel mulching was an effective strategy to increase soil temperature and moisture and, therefore, crop production; this method was recently replaced by plastic film mulching with the onset of industrial development. This study aimed to evaluate the effects of the two mulching methods on the crop growth, yield, and water-use efficiency of maize (Zea mays L.). Three treatments [non-mulched (CK, control), gravel-mulched (GM) and plastic film-mulched (FM)] were compared in 2010 and 2011 at the Changwu experimental station. Compared to CK, both gravel and plastic film mulching increased the cumulative soil thermal time (TTSoil) by 150–220°C over the growing season. During seedling stage, the FM treatment increased the TTSoil by 50°C in 2010 and by 79°C in 2011, which was higher than that caused by GM treatment by 37°C and 41°C, respectively. The higher soil temperatures in the FM treatment significantly accelerated maize growth and development more than the GM treatment. The FM treatment stimulated the highest growth rate during vegetative stages, as indicated by a greater leaf area index and the intercepted photosynthetically active radiation, and consistently produced the highest shoot biomass throughout the growing season. Compared with the CK, the grain yields increased by 17.0% and 28.3% in 2010, and 70.2% and 87.5% in 2011 (a colder year) for the GM and FM treatments, respectively. Similarly, water-use efficiency was improved by 15% and 23% in 2010, and by 51% and 90% in 2011 for the GM and FM treatments, respectively. Overall, we concluded that plastic film mulching, compared to gravel mulching, was more effective at counteracting the region's water limitations and low temperatures.
