Abstract: The characteristics of soil aggregates under different yield levels in dry wheat fields in Xinjiang were analyzed by wet sieve method. The results showed that there were differences in the size of water stable aggregates in soil at different yield levels. The soil aggregates of >5 mm particle in high-yield field soil were significantly higher than those of medium-yield and low-yield fields, increased by 45.18% and 52.72%, respectively; The soil aggregates of 0.25~0.5 mm particle in high-yield fields and medium-yield fields were significantly higher than those in low-yield fields, increased by 45.70% and 51.15% respectively; The soil aggregates of <0.25 mm grain in low-yield fields increased significantly by 36.34% and 8.84% compared with high-yield fields and medium-yield fields. The content of large aggregates in the soil of >0.25 mm particle size in high yield field reached 68.30%, increased by 13.29% and 20.29% respectively over the middle and low yield fields. The mean weight diameter （MWD） and geometric mean diameter （GMD） of soil all showed that high-yield fields was the highest, medium-yield fields was second, and low-yield fields was the lowest. But the fractal dimension is opposite. The fractal dimension of soil was significantly negatively correlated with MWD, GMD and the soil aggregates of >5 mm particle, and was significantly positively correlated with <0.25 mm particle. MWD, GMD were significantly positively correlated with the soil aggregates of >5 mm particle, and significantly negatively correlated with the soil aggregates of <0.25 mm particle.

Key words: rain-fed dryland, aggregates, Yili valley