Abstract: 【Objective】Tillage will greatly influence the aggregation and stability of soil aggregates. The paper studied the effects of conservation tillage on the soil aggregates characteristics. 【Method】Soils from No-tillage (NT), Rotary tillage (RT) and conventional tillage (Moldboard tillage, CT) plots witch lasted 4 years (2001-2005) at the Luancheng Research Station in Hebei Province were sampled, and the aggregates amount, size distribution and fractal dimension were examined by dry and wet sieving methods. 【Result】Results indicated that NT significantly increased the topsoil (0-5cm) bulk density (BD), while RT maintained lower BD as CT except for significant increase at 10-20cm. Dry sieving results showed that NT resulted in higher Macro-aggregates content (R0.25), mean weight diameter (MWD) and Geometric Mean Diameter (GMD) than other treatments at 0-10cm, while RT showed no difference with CT. Wet sieving results showed that most of the aggregates are unstable, and the MWD and GMD of water-table aggregates showed the same trend: NT>RT>CT. At 0-5cm, the fractal dimension (D) of water-stable aggregates under NT was lower than RT and CT; while at 5-10cm, RT yielded highest , showed worst stability. 【Conclusion】After 4 years experiment, NT increased the aggregation and the stability of soil aggregates, while duo to intense disturbance, the aggregation and stability within tillage depth under RT and CT decreased; at 10-30cm, no significant difference had been yielded among the three tillage systems.

Key words: Conservation tillage, Soil aggregate, Fractal dimension, MWD, GMD