Microplastics
(MPs) accumulation in agricultural soils has shown
serious implications for soil ecosystem functions. Ammonia (NH3) volatilization is a major pathway of nitrogen loss in agricultural
systems, while its response mechanism to MPs occurrence, particularly
the role of MPs size and natural aging, has been scarcely explored.
In this study, polyethylene terephthalate of sizes of 10 μm
(PET10) and 200 μm (PET200) were selected in a rice–wheat
rotation cycle soil system. Results showed that PET10 and PET200 reduced
soil NH3 volatilization cumulative amount from 58.9 to
18.6–40.3 kg N/ha and yield-scaled loss from 2.95 to 0.92–1.60
kg/t grain. Reduction of NH3 volatilization occurred in
both the rice growth season and the subsequent wheat growth season,
in which two MPs were aged in the initial rice season, with verification
by 2.8 wt % more bulk oxygen of PET200 separated from the soil after
rice harvest. Moreover, PET200 treatment showed 7.7–25.9% less
cumulative NH3 volatilization than PET10, which was significant
in the rice growth season. This was partially related to the higher
adsorption capacity (10.6 mg/g) for free NH4
+–N of PET200 and 5.2% more microaggregate (<250 μm)
formation in PET200 treatment. These findings provide references for
the assessment of MPs effects on soil nitrogen biogeochemical cycling.