Individual and mixed effects of slag and biochar on soil aggregates and their carbon concentration and on fungal community structure in subtropical early‐ and late‐cropping paddy fields

Abstract Aggregates are the basis for the formation of a good soil structure. Soil fungi community plays an important role in soil nutrient transformation, soil aggregate formation and ecological balance of the plant–soil system. However, little is known about the multi‐year response of soil aggregates, their carbon concentrations and fungal community structure to different exogenous agents in double cropping paddy fields in southern China. Therefore, we studied the changes of aggregates' carbon concentrations and stability and fungal community structure under the application of slag and biochar individually and mixed in paddy fields in southeastern China for two annual cycles. Geometric mean diameter in the 0–15 cm layer in the early paddy fields was 29.0% lower in the slag + biochar treatment than in the control. The percentage of soil carbon concentrations in aggregates <0.25 mm in the four treatments in the early paddy field was 35.5%, 38.6%, 45.8% and 51.2%, respectively, in the 0–15 cm layer and 36.1%, 33.8%, 54.9% and 50.9%, respectively, in the 15–30 cm layer. Thus, treatments including biochar increase aggregates carbon concentration probably due to carbon retained in the biochar. Amendments with biochar and slag affected the fungal community structure even 2 years after their application. The results of this study reveal the relationship between soil aggregates and their carbon concentration and fungal community structure in paddy fields under slag and biochar application. These findings provide a theoretical basis for sustainable agricultural applications.