In arid and semi-arid regions, plastic film mulching can effectively improve crop yield, but with the increase of service life, a lot of residual plastic film (R_PF) remains in the soil. The application of a R_PF to a soil will alter soil moisture processes, and thus, affect the soil water distribution and its effectiveness. A quadratic regression orthogonal design was used to study the effects of initial moisture content (I_MC), dry bulk density (D_BD), residual plastic film content (R_PFC), and the burial depth of R_PF on the migration time of wetting front (M_F), moisture content (M_C), and accumulative infiltration (A_I) of a test soil. It was found that I_MC, D_BD, and R_PFC were the main factors affecting M_C, M_F, and A_I, while the burial depth of R_PF had no significant influence. The order of influence for the factors affecting M_F was I_MC > D_BD > R_PFC, while the order of influence for the factors affecting M_C and A_I was D_BD > I_MC > R_PFC. R_PFC was parabolic in relation to M_F, M_C, and A_I, when it was in the range of 50–100 kg/hm², while within the same range M_C and A_I reached a maximum and M_F reached a minimum. The analysis of the interactive responses revealed that when the D_BD was greater than 1.29g/cm³, the M_F initially decreased and then increased with the increase of R_PFC. When the R_PFC was more than 100 kg/hm², the M_F initially increased and then decreased with the increase of the D_BD. When the D_BD was larger than 1.31 g/cm³, the A_I initially increased and then decreased with the increase of R_PFC. It was apparent that the R_PF not only had a blocking effect on the wetting front, but also affected the water flow. When the R_PFC was between 50 and 100 kg/hm², the soil M_C was significantly increased. It was suggested that the R_PF pollution area should increase the mechanical recovery of plastic film, standardize the use and recycling of agricultural R_PF, optimize the planting model, and establish a recyclable model for the treatment of R_PF pollution, and it was proposed that the R_PFC remaining after recovery of the R_PF should be less than 50 kg/hm².This study can prove the law of soil water movement in the residue film pollution area and provide reference and solution ideas for the comprehensive treatment of residue film pollution in farmland.

Biochar as an organic soil conditioner has colossal application potential. Many recent studies revealed the influence of biochar on the soil during the crop growth period. However, few studies considered the effect of seasonal freeze-thaw on biochar’s improvement effect. Therefore, we conducted a field experiment to observe the impact of biochar on soil and cotton (Gossypium hirsutum L.). We used four biochar application rates (0.33%, 0.66%, 1.00%, and 1.33% of soil mass fraction) and applied biochar in the cotton field before and after seasonal freeze-thaw, respectively. The results showed that applying biochar after freeze-thaw was more effective on soil water storage and soil temperature preservation during the cotton growth period. Moreover, applying biochar with 0.66% soil mass fraction after freeze-thaw improved the cotton biomass by 5.31~36.13%, leaf area index by −10.82~32.52%, and seed cotton yield by 3.88~21.98%. Based on the principal component analysis of cotton fiber quality, we found that 0.66% biochar application after freeze-thaw improved cotton fiber most significantly. In total, applying biochar at 0.66% soil mass fraction after freeze-thaw was the most optimal application mode for improving soil hydrothermal conditions, cotton growth, and fiber quality. Our study can provide a scientific reference for applying biochar in northern Xinjiang, China.