Microplastics change the leaching of nitrogen and potassium in Mollisols

Nowadays, the dynamics of nutrients leaching from the soils and their driving mechanism have been focused on, however, it is still unclear how microplastics (MPs) influence the nutrients' leaching in soils. In this study, five concentrations (w/w, 0.0 %, 0.5 %, 1 %, 2 %, 3 %) and three sizes of MPs of polyethylene (PE) (0.15-0.36 mm, 0.36-0.60 mm and 0.60-1.00 mm) influencing the leaching of NO₃^--N and water-soluble potassium (WSK) was simulated by a column method in Mollisols, and both the pre-fertilization and post-fertilization were considered. The results showed that, before KNO₃ addition, there was a negative power function relationship between the NO₃^--N concentration and the leaching solution volume/leaching time. The amount and concentration of NO₃^--N leaching was higher in the early leaching stage. Compared with the CK, PE_0.5% significantly reduced the leaching amount of WSK, while increased the leaching amount of NO₃^--N but not significantly. The leaching amount of WSK decreased with the increasing size of PEMP when the PEMP concentration was the same, while NO₃^--N was opposite. PE_0.60-1.00 increased the leaching amount of NO₃^--N, while reduced the leaching amount of WSK. After KNO₃ addition, compared with CK, PE_1% significantly reduced the leaching amount of NO₃^--N, and PE_1% had the lowest leaching amount of WSK. However, when the PEMP concentration in the soil reached a certain threshold (w/w, >1 %), the leaching amount of NO₃^--N and WSK increased gradually with PEMP increasing. PE_0.60-1.00 reduced the leaching amount of NO₃^--N and WSK most obviously. In general, low concentrations (w/w, <1 %) and large sizes (0.60-1.00 mm) of PEMP promoted NO₃^--N leaching and inhibited the WSK leaching from the soil before the addition of KNO₃, however, they both inhibited the leaching of NO₃^--N and WSK from the soil after addition of KNO₃.