Tillage strongly affects the process of soil aggregate stabilization, which involves a variety of binding mechanisms interacting at a range of spatial scales. To understand how binding mechanisms interact to promote soil aggregation, the impacts of three tillage systems (no tillage (NT), ridge tillage (RT) and conventional tillage (CT)) on soil aggregate binding agents (i.e., organic carbon (SOC), microbial biomass and glomalin-related soil proteins (GRSPs)) and aggregation were studied in the black soil of Northeast China. Compared with CT, RT increased all the aggregate-associated SOC, and NT only increased the SOC in the microaggregates. However, the contents of microbial biomass and GRSPs within bulk soil and different aggregate fractions were higher in NT and RT than in CT. Among the four aggregate fractions, greater values of SOC, microbial biomass and easily extractable GRSP (EEGRSP) were found in microaggregates and macroaggregates, respectively; while the total GRSP (TGRSP) was distributed equally among aggregate fractions. Structural equation modelling revealed that SOC, microbial biomass, and GRSPs accounted for 79% of the variation in soil aggregation. Soil organic carbon influenced aggregate stability indirectly through the effects on MBC and MBN. Microbial biomass and glomalin were more important driving factors for aggregate stability in the RT and NT systems. Our results suggest that conservation tillage (RT and NT) is beneficial for soil structure due to its positive effects on aggregation processes in black soil region of Northeast China.
