Objectives  This study was carried out to compare the effects of inorganic and organic amendments on aggregate formation and crop yields in sandy fluvo-aquic soil, and to provide a theoretical basis for the application of new soil amendments.

Methods  A 4-year field experiment was carried out under a wheat-maize rotation system in Langfang, Hebei Province. The experiment included four treatments: chemical fertilizer only (CK), chemical fertilizer + inorganic soil amendment (SA), chemical fertilizer + organic soil amendment (SC), and chemical fertilizer + organic soil amendment + inorganic soil amendment (SCA). Following wheat and maize harvest in 2019, soil samples were collected from the surface layer (0–20 cm) and soil chemical characteristics, microbial biomass, water-stable soil aggregate distributions and stability were measured.

Results  Wheat and maize yields significantly increased by 54.16% and 24.26%, respectively, under SCA compared to CK. Soil chemical properties (total N, soil organic C, readily available K and available P) significantly increased under SC than CK in wheat season and under SCA than CK in maize season. Microbial biomass C also increased significantly under SC by 8.82% in the wheat season and 33.65% under SCA in the maize season. Furthermore, soil aggregate significantly increased under SC and SCA than CK in both wheat and maize season, with the major particle sizes ranging from 0.25～0.053 mm. Compared to CK, a (P < 0.05) higher percentage of water-stable aggregates (20.35%), aggregate stability (mean weight diameter = 22.41%) and aggregation (42.51%) was recorded in particle sizes > 0.25 mm under SC in wheat season. However, in the maize season, these parameters respectively increased by 29.65%, 35.47%, and 68.71% under SCA. SCA was the best treatment for aggregate formation and stability. SCA increased soil organic C and total N contents the most in the particle sizes > 0.25 mm aggregate. Aggregates in the particle sizes > 0.25 mm fraction had significantly higher contribution rate to SOC and TN, while aggregates in the particle sizes < 0.053 mm fraction significantly decreased the contribution rate under both inorganic and organic amendments. Both redundancy analysis and structural equation model showed that aggregate composition was positively correlated with soil available P, microbial biomass carbon and organic carbon content of aggregates and negatively correlated with soil pH.

Conclusions  Application of organic amendment or combined application of organic and inorganic amendment in sandy fluvo-aquic soil is an important method for improving soil chemical properties, macro-aggregate formation and aggregates stability. Aggregate stability can improve crop yield by changing soil C/N.