Impact of Plastic Film on Yield of Potato in Whole China: Meta Analysis of 30-Year Results from Field Experiments.

Potato has been considered as the fourth largest food crops in China and it is important to enhance potato yield. As one of important techniques to improve potato yield, plastic film mulching has been widely applied but it is unclear about if and how the yield-increasing effect of plastic film is affected by different areas, colors of plastic film, planting methods, and main climatic factors (temperature and precipitation) in China. Therefore, we collected 30-year experimental data on potato yield under plastic film mulching from published papers in order to investigate the yield-increasing effect of potato in different areas, covered with black or white films, planted in flat field or on ridges, during the period from 1984 to 2014 by using Meta-analysis method. Meta-analysis method can quantatively synthesize the results from studies on a same subject and has been used for soil carbon emission but rarely been used in agricultural yield. For Meta-analysis, a total of 52 groups of data were used and they were associated with 14 provinces in China distributed in northwest, southwest, and southeast. Results showed that: 1) The yield-increasing effects of plastic films were highest in the northwest with a mean relative yield-increasing rate of 35.6%, followed by the southeast and southwest with the mean yield-increasing rate of 20% and 12%, respectively; 2) The yield-increasing rate of potato was higher during the period from 1990 to 2010 than before, but getting lower after the year of 2010 with minus yield-increasing values reported, revealing an upward-to-downward trend during the past 30 years; 3) The yield-increasing effects of white films were not significantly different from those of black films; 4) The yield-increasing effects were not significantly different between the ridge and flat field planting methods; 5) The yield-increasing effects of plastic films were high under regions with mean annual precipitation smaller than 500 mm and mean annual temperature lower than 10 oC with relative yield-increasing rate of 40.5% and 37.6%, respectively. Moreover, an in-depth analysis of the upward-to-downward trend of yield-increasing effects under plastic film mulching during the past 30 years in China suggested that negative effects of plastic films on potato yield became obvious recently, after 2010. This study helps to understand status of plastic films application in potato production in China and provides data support for application of plastic films in different regions in China. Keywords: potato production, Meta analysis, plastic film, China, yield-increasing effect, negative effect