Testing biodegradable films as alternatives to plastic films in enhancing cotton (Gossypium hirsutum L.) yield under mulched drip irrigation

To alleviate soil pollution caused by mulching polyethylene (PE) films that are non-degradable and non-recoverable, we evaluated different biodegradable (BD) films (starch-polymer, polybutyrate adipate terephthalate or PBAT, and butylene succinate-co-butylene adipate or PBSA) as alternatives to PE films for mulched drip irrigation in a cotton (Gossypiwn hirsutum L.) field in Xinjiang, the largest cotton-planting region in China. Film degradation, soil salinity, residue film accumulation, cotton yield, and water use efficiency (WUE) were compared between BD and PE films in two consecutive years (2015-2016). We found that the accumulation of residual film was significantly stronger in plots covered by PE films than by BD films. At the early stage of cotton growth, BD and PE films performed similarly in conserving water in topsoil (0-40 cm depth). Degradation of BD films initiated 40-60 days after sowing. Thus, at the late stage of cotton growth, PE films remained intact and were more effective than BD films in wetting the soil. Due to the drier soil, soil salinity in plots covered by BD films was higher than those by PE films. PBAT films showed a slower degradation process than PBSA and starch films under the mulching condition but degraded more completely after buried in soil. After mulched drip irrigation was managed for two years, cotton yield showed no significant difference between plots with PE films (5722 kg ha(-1)) and those with thicker PBAT films (5699 kg ha(-1)). However, mulching PE films resulted in a significantly higher WUE than BD films. Therefore, we suggest thicker PBAT films (with the highest yield and WUE and the lowest accumulation of residual film) as potential alternatives to PE films to improve cotton yield and control soil pollution under mulched drip irrigation.