Variations in soil aggregate distribution and associated organic carbon and nitrogen fractions in long-term continuous vegetable rotation soil by nitrogen fertilization and plastic film mulching

Small changes in soil aggregates-associated organic carbon (OC) can induce huge fluctuations in greenhouse gas emissions. However, there is a knowledge gap on the responses to nitrogen (N) fertilization under plastic film mulching, especially in long-term continuous rotation systems. This study assessed the impacts of plastic film mulching and N fertilization on the soil aggregate distribution and associated OC and N fractions in a 10-year continuous cucumber-cabbage rotation soil (0–40 cm). The impacts also were further quantified using the design of experiment (DOE) method. Plastic film mulching alleviated the impact of N fertilization on soil aggregate stability, which declined under higher N doses. Plastic film mulching coupled with N fertilization resulted in higher contents of soil OC and dissolved OC in macroaggregates but lower contents in silt+clay- aggregates. The total N and dissolved organic N (DON) contents in different aggregates varied significantly with N application doses, and the alternations were impacted by plastic film mulching, which improved the DON distribution in larger agglomerates, especially at medium and high N doses. Soil aggregate distribution and associated OC and N fractions did not show consistent trends in different soil depths, which was attributed to the contributions of plastic film mulching, N fertilization and their interactions. The study suggests that N fertilizer should be applied under plastic film mulches at appropriate levels to improve C assimilation and soil fertility and promote the sustainable development of long-term vegetable rotation systems.