When does plastic-film mulching yield more for dryland maize in the Loess Plateau of China? A meta-analysis

Plastic-film mulching (PM) has been widely adopted for dryland maize (Zea mays L.) in the Loess Plateau of China, whereas its impact on grain yield (GY) varies considerably. Therefore, it is crucial to make some feasible strategies that aim to improve the productivity of PM systems. Using the data obtained from peer-reviewed publications, we conducted a meta-analysis to (1) analyze the climate regions where maize GY increase induced by PM (GY-I) was greater than zero and (2) determine the optimum conditions of soil properties and field management practices for PM application considering both GY-I and actual GY under PM (GY-P). The results showed that on average, PM significantly increased maize GY by 56.10%, as compared with no-mulching, which was a result of increased aboveground biomass at harvest, harvest index, ear number per square meter, kernel number per row, and hundred kernel weight. PM could extend maize cultivation to drier and colder areas with mean annual precipitation (MAP) of 203.8-281.3 mm and mean annual temperature (MAT) of 3.3-4.6 degrees C, where an average GY of about 1866 kg ha(-1) could be achieved under PM. However, as MAP and MAT continued to increase, GY-I decreased linearly and reached zero at MAP and MAT of 627.6 mm and 13.1 degrees C, respectively. GY-I and GY-P were both significantly affected by soil bulk density (SBD), plant density (PD), nitrogen fertilizer rate (NFR), and phosphorus fertilizer rate (PFR). Increasing SBD, NFR, and PFR tended to reduce GY-I, but GY-P showed an inverted U-shaped relationship with SBD and changed from increasing to constant with increasing NFR and PFR. As PD increased, GY-I decreased at first and then increased, while GY-P was observed to change oppositely. It was suggested that PM be adopted at SBD, NFR, PFR, and PD of 1.14-1.30 g cm(-3), 160-220 kg N ha(-1), 105-135 kg P2O5 ha(-1), and 72,000-80,000 plants ha(-1), respectively. In conclusion, PM usually has a positive effect on maize production in the Chinese Loess Plateau. However, for optimizing the PM effect in practice, we must consider climate, soil properties, field management practices, GY-I, and GY-P.