Is biodegradable film an alternative to polyethylene plastic film for improving maize productivity in rainfed agricultural areas?-Evidence from field experiments

Due to increasing concerns regarding plastic pollution throughout the world, biodegradable mulch is considered a promising alternative to polyethylene film and its suitability has been verified in some crops. However, it is unclear whether the long-term continuous use of biodegradable mulch as a substitute for polyethylene film is sustainable in rainfed agricultural areas, and whether its effect is consistent under different climatic conditions. Therefore, we conducted 7-year (2013-2019) and 4-year (2015-2018) field experiments in two regions with different precipitation levels (semiarid and semi-humid regions) on the Loess Plateau in China. We compared the effects of polyethylene film mulching (PM), biodegradable film mulching (BM), and traditional flat planting without film mulching (TF) on the soil temperature, soil moisture, grain yield, crop water productivity (WPc), and economic benefit (EB). The results showed that compared with TF, the grain yields under BM and PM increased by 2.1-93.3% and 7.6-34.6%, respectively, WPc increased by 2.1-93.3% and 7.6-34.6%, and EB increased by -16.6-131.5% and -7.8-27.0%. The differences in these indexes under the two mulching methods mainly occurred in the dry years with less precipitation in the semiarid region, whereas there were no significant differences in the grain yield, WPc, and EB under BM and PM in the semi-humid region. Therefore, the decision regarding whether BM can replace PM to improve maize productivity is significantly affected by the annual precipitation in rainfed areas. Furthermore, the univariate quadratic equation model was used to simulate that BM can obtain a higher crop yield and EB than PM when the precipitation is more than 600 mm and less than 800 mm, so as to achieve a win-win situation with continuous yield and income increases, and environmental friendliness in the Loess Plateau of China. However, the yield increase effect of plastic film mulching is also related to crop types, mulch types and farming practices except for climate. In addition, reducing the production cost will still be important for encouraging farmers to use biodegradable film instead of polyethylene film.