Effects of lucerne-crop rotation patterns on soil aggregate stabilityand soil organic carbon

A local experiment of lucerne-crop rotation system was conducted on dry farmlands of the Loess Plateau in Central Gansu Province to determine the distribution characteristics of soil aggregate stability and soil organic carbon. The experiment included six rotation patterns — lucerne-lucerne (LL), lucerne-fallow (LF), lucerne-wheat (LW), lucerne-corn (LC), lucerne- potato (LP) and lucerne-millet (LM). Soil aggregate characteristics and organic carbon content were investigated after crop harvest. The results showed that ≥0.25 mm aggregate was the dominant component of the mechanically stable aggregates of soil, which accounted for >72.17% of the mechanically stable aggregates. However, the <0.25 mm aggregates was the dominant component of the water stable aggregates, which exceeding 95.18% of the water stable aggregates. The content of the?≥0.25 mm aggregates of soil and its mean weight diameter (MWD) increased with increasing soil depth, while larger water stable aggregates content and MWD were irregularly changed. Compared with LL treatment, the ≥0.25 mm aggregates contents of LC and LP treatments increased by 5.94% and 1.12%, respectively, at soil depth of 030 cm. The MWD in LC treatment was the highest among all treatments. Soil organic carbon (SOC) content decreased with increasing soil depth in all rotation patterns. Compared with LL rotation pattern, SOC contents in LF, LC, LP and LM treatments all declined to different extents at 030 cm soil depth, especially, it significantly decreased by 18.68% in LP treatment. The correlation analysis indicated that SOC content had significantly positive relation with water stable soil aggregates of 25 mm, 12 mm, 0.51 mm, 0.250.5 mm and MWD, while it had significantly negative relation with <0.25 mm soil aggregate content. In conclusion, LC rotation pattern significantly increased the mechanical stability of soil aggregates. However, the effect of different rotation patterns on water stable soil aggregates was negligible. Furthermore, SOC content significantly influenced the formation and stability of water stable aggregate.