Integrated effects of plastic film residues on cotton growth and field carbon sequestration under drip irrigation in arid oasis regions

Mulched drip irrigation is the primary irrigation technology for cotton (Gossypium hirsutum L.) cultivation in arid and semi-arid regions. In recent years, the increasing amount of residual plastic film (RPF) in mulched cotton fields has posed a more significant threat to soil quality and the sustainability of agricultural production. However, the relationship between different soil RPF amounts and cotton growth, yield, and carbon balance in cotton fields is unclear. In this study, six RPF amounts, namely RPF₀ (0 kg ha–¹), RPF₅ (146.18 kg ha–¹), RPF₁₀ (228.03 kg ha–¹), RPF₁₅ (309.88 kg ha–¹), RPF₂₀ (391.73 kg ha–¹), and RPF₂₅ (473.58 kg ha–¹), were set in a two-year (2020–2021) field experiment to investigate their effects on cotton growth, yield, field CO₂ emissions, and carbon sequestration. Results showed that cotton growth indicators (Plant height, stem diameter, leaf area index, biomass of each organ) at different growth stages and yield indicators (Single boll weight, per plant bolls number, seed cotton yield) were significantly negatively correlated (p < 0.05) with the soil RPF amount. The RPF₂₅ treatment showed yield decreases of up to 33.4% and 43.2% in these two years, respectively, compared with the RPF₀ treatment. Surprisingly, the presence of RPF in soil reduced the rate and cumulative CO₂ emissions from cotton fields during the growth and fallow periods, but carbon sequestration in cotton fields decreased significantly with increasing RPF amounts (15.05%~60.98% in 2020 and 17.38~76.81% in 2021). RPF inhibited cotton root growth, reducing plant biomass accumulation, decreasing seed cotton yield, and weakening cotton fields' carbon sink. When the RPF amount in the soil was less than or equal to 228.03 kg ha–¹, cotton economic benefits and field carbon storage were not unduly weakened. The second-year indicators of cotton fields with the RPF were significantly lower than the first year, and the permanent residue of soil RPF also created a more hostile crop growing environment. We concluded that the RPF amount in fields should be reduced as soon as possible and that more environmentally friendly and carbon-reducing mulching materials should be used instead of plastic film.