Background Soil carbon (C) and nitrogen (N) content plays a key role in nutrient utilization and cycling of farmland crops. The carbon and nitrogen content and stability of soil aggregates are important indicators to characterize soil structure, degradation and stability. Ginger-rice rotation and ginger-vegetable rotation are different patterns of paddy and dry land rotation, which have different carbon and nitrogen protection mechanisms. This work aims to explore the distribution patterns, stability and variation characteristics of C and N content of farmland soil aggregates under different rotation patterns, and to select the optimal rotation pattern.

Methods In this study, the farmland under the ginger-vegetable and ginger-rice rotation patterns was used as the research object of Tongling city, Anhui province, and soil samples with a depth of 0-20 cm were collected. The contents of soil aggregates with different particle sizes were measured, and the differences of soil aggregates and C and N contents were analyzed by ANOVA. The qualitative characteristics of soil aggregate stability were measured by the soil aggregate stability index mean weight diameter (MWD), geometric mean diameter (GMD), > 0.25 mm diameter aggregate (DR_0.25) and fractal dimension (D), and the relationship between soil aggregate, aggregate carbon and nitrogen and soil stability index was analyzed by Person correlation.

Results 1) The content of >0.053-0.25 mm microaggregates in the ginger season under the ginger-vegetable rotation increased by 53% compared with that in the vegetable season (P < 0.05). Under ginger-rice rotation, the content of microaggregates≤0.053 mm in the ginger season was 39% lower than that in the rice season (P < 0.05), while the content of large aggregates >0.25-1.00 mm was about twice higher than that in the rice season (P < 0.05). 2) Compared with the ginger-rice rotation, the ginger-vegetable rotation significantly reduced the C and N content of ≤0.053 mm microaggregates in the ginger season by 32% and 33% (P < 0.05), and the C and N content of the large aggregates >1.00 mm significantly reduced, respectively, in 39% and 33% (P < 0.05). 3) Under the ginger-rice rotation, the contribution rate of ginger >1.00 mm large aggregate C was significantly higher than that of ginger-vegetable rotation by 24% (P < 0.05), and the contribution rate of >0.25-1.00 mm large aggregate C and N was significantly lower than that of ginger-vegetable rotation 32% and 25% (P < 0.05). 4) GMD and DR_0.25 was significantly positively correlated with the content of >0.25-1.00 mm large aggregate (P < 0.01). MWD was positively correlated with the content of >1.00 mm aggregates, respectively (P < 0.01). MWD, GMD, and DR_0.25 were all significantly positively correlated with the C and N of larger aggregates >0.25 mm (P < 0.05).

Conclusions Compared with the dry land rotation under the ginger-vegetable rotation, the ginger-rice rotation pattern under the paddy dry rotation can continuously improve the stability of soil aggregates and maintain the efficient utilization of soil C and N nutrients. It is the optimal rotation pattern to realize the coordinated utilization of soil and water conservation and nutrients in Tongling city, which is conducive to the sustainable production of white ginger.