Moisture and root systems affect the turnover of soil aggregates during various crop growth periods

• Macroaggregates tended to break into the size fraction of 0.25–0.053 mm. • Turnover rate of aggregates were related to soil moisture content indices. • The correlation between roots morphology characteristics and aggregates occurs in periods emergence and full pod. Soil moisture conditions and crop root growth collectively influence the turnover (breakdown–buildup) of soil aggregates during different crop growth periods. However, evaluations of these effects under actual field conditions have been limited. Therefore, aggregates of Mollisols from cultivated land (1–10 cm) were taken as the research objects. Aggregates in four size fractions (A: 5–2 mm, B: 2–0.25 mm, C: 0.25–0.053 mm, D: < 0.053 mm) were tracked using the rare earth element (REE) tracing method during soybean growth periods (Ⅰ: planting, Ⅱ: emergence, Ⅲ: second trifoliolate, Ⅳ: fifth trifoliolate, Ⅴ: full bloom, Ⅵ: full pod, Ⅶ: full seed, VIII: harvest). The key findings were as follows: i) The aggregate composition was predominantly size fraction C, which accounted for 34.53–43.41 % during the soybean growth periods. The mean weight diameter ( MWD ) displayed a bimodal pattern, with peaks of 0.44 and 0.41 observed in II and VI, respectively. ii) Approximately 33.13–46.16 % of the aggregates in size fractions A and B tended to break into size fraction C during soybean growth, with neighboring size fractions contributing 18.62–48.60 % to the aggregate formation process. The turnover rate ( TR ) of size fraction D was the highest. iii) Soil moisture conditions were significantly correlated with the TR of each size fraction during the growth periods ( P < 0.05). iv) The root morphological characteristics of the < 2 mm aggregates were significantly negatively correlated with the TRs of size fractions B and C in V, but positively correlated with the TRs of size fractions B, C and D in VI. The study reveals significant variations in aggregate turnover patterns across different growth stages, providing valuable insights into the evolution of soil structural properties in cultivated lands.