Effects of the key environmental and management factors on the advantages of film mulching spring maize in northwest China: A meta-analysis

Film mulching (FM) have been widely adopted to increase crop yields in semi-arid and arid regions in northwest China. So far, there are some effects of FM on coupling mechanism water-carbon/nitrogen use in dry-farming agriculture, but it's still not clear. Therefore, this study of FM impacts on spring maize yield, evapotranspiration (ET), total nitrogen uptake (TNU) of above-ground parts and water use efficiency (WUE) are necessary. We conducted a meta-analysis of FM, including 108 studies in northwest China. Overall, FM significantly increased spring maize yield, ET, TNU and WUE by ca. 50.7%, 2.6%, 56.4% and 50.2%, respectively. When growth period rainfall (GPR) is between 200 and 400 mm, the effects of FM on yield, ET and TNU were the strongest, while at GPR < 200 mm, the effects of FM on WUE were the strongest. The effect sizes of FM on yield, TNU and WUE increased with the increase of altitude, while the maximum effect size of ET appeared in the range of 1000-2000 m. On the basis of FM, further increasing the plant density (at PD> 75000 plant ha-1) can also increase the yield, ET, TNU and WUE by ca. 61.8%, 7.3%, 80.2% and 54.7% respectively. The effect sizes of FM on yield, ET, TNU and WUE increased first and then decreased with the increase of total nitrogen amounts (TNA), and the maximum effect values appeared in the range of 200-300 kg ha-1. In conclusion, FM can improve the adaptation threshold of spring maize to drought and high altitude. Moreover, spring maize yield was mainly co-determined by growth period rainfall, altitude, planting density, total nitrogen application and other factors.