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, how-ever, it is still unclear how microplastics (MPs) influence the nutrients' leaching in soils. In this study, five concentra-tions (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 col-umn 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, PE0.5% significantly reduced the leaching amount of WSK, while in-creased the leaching amount of NO3--N but not significantly. The leaching amount of WSK decreased with the increas-ing size of PEMP when the PEMP concentration was the same, while NO3--N was opposite. PE0.60-1.00 increased the leaching amount of NO3--N, while reduced the leaching amount of WSK. After KNO3 addition, compared with CK, PE1% significantly reduced the leaching amount of NO3--N, and PE1% had the lowest leaching amount of WSK. How-ever, 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. PE0.60-1.00 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.

Automated summary

This study simulated the influence of polyethylene microplastics (PEMP) on the leaching of NO3--N and water-soluble potassium (WSK) in soils. The results showed that the concentration and size of PEMP had different effects on nutrient leaching. Before the addition of potassium nitrate (KNO3), low concentrations and large sizes of PEMP promoted NO3--N leaching and inhibited WSK leaching, while after the addition of KNO3, they inhibited the leaching of both NO3--N and WSK.