季节性冻融对机械压实黑土微团聚体特征的影响

Effects of seasonal freeze and thaw cycles on the micro-aggregate characteristics of the mechanically compacted black soil

采用田间模拟机械压实的方法,通过对连续两季季节性冻融后不同深度(表层0~20 cm、亚表层20~40 cm和下层40~80 cm)不同压实次数(0、3和12次)土壤水稳性微团聚体组成(≥0.25 mm、0.25~0.05 mm、0.05~0.02 mm、0.02~0.002 mm、<0.002 mm粒级)、分形维数(D)和分散系数等特征指标的测定、计算与分析,研究了两季季节性冻融对黑土区0~80 cm土层范围内土壤微团聚体特征的影响,讨论了季节性冻融与机械压实的交互作用。结果表明:季节性冻融对不同深度黑土微团聚体组成及稳定性的影响不同,主要表现为增加表层土壤微团聚体的稳定性,降低亚表层和下层土壤微团聚体的稳定性,且连续两季冻融对黑土微团聚体组成及稳定性的影响也存在差异,1季冻融主要显著增加无压实土壤微团聚体的稳定性,而2季冻融却显著降低无压实土壤微团聚体的稳定性;两季冻融结束后,3次压实土壤微团聚体D值和分散系数均高于对照(P<0.05),尽管12次压实土壤分散系数同样高于对照(P<0.05),但土壤微团聚体D值与对照相比无显著差异,季节性冻融与机械压实的交互作用主要表现为季节性冻融加剧少次压实土壤微团聚体的破坏、降低其稳定性,而对多次压实土壤微团聚体的组成及稳定性有一定的恢复作用。

Based on the simulation of mechanical compaction in the field,the impacts of seasonal freeze and thaw cycles on soil micro-aggregates composition and stability were revealed in the vertical range by measuring and analyzing the soil micro-aggregates distribution（ ≥0. 25 mm,0. 25-0. 05 mm,0. 05-0. 02 mm,0. 02-0. 002 mm, 〈0. 002 mm）,fractal dimension（ D） and dispersion coefficient in two consecutive years at different soil depths（ 0-20 cm,20-40 cm,40-80 cm） of different compaction passes（ no compaction,3 passes,12 passes）,and the interaction effects between seasonal freezingthawing cycles and mechanical compaction were discussed emphatically. The results showed that the effects of seasonal freeze and thaw cycles on the composition and stability of micro-aggregates in black soil were different at varied soil depths,the stability of soil micro-aggregates mainly increased in the surface soil layer（ 0-20 cm） after seasonal freeze and thaw cycles,while decreased in other soil layers.Simultaneously,the effects of seasonal freeze and thaw cycles were also different from year to year. The first seasonal freezing-thawing process mainly increased the micro-aggregates stability of the uncompacted soil,but the second seasonal freezing-thawing processes reduced the stability of the soil micro-aggregates significantly. However,it is worth noting that the interaction effects between seasonal freezing-thawing cycles and mechanical compaction on the soil micro-aggregates characteristics were more complicated.After two seasonal freezing-thawing processes, the D value of soil micro-aggregates and dispersion coefficient were significantly higher than control condition（ P〈 0. 05） when the mechanical compaction treatment was only 3 compaction passes,although the soil dispersion coefficient was also higher than control（ P 〈0. 05） when the mechanical compaction passes increased to 12 times,the D value of soil micro-aggregates was no significant difference compared with the control. In general,the seasonal freeze and thaw cycles generally exacerbated the damage of micro-aggregates and reduced the stability when the soil was compacted only a few times,but displayed a certain recovery characteristic when the mechanical compaction passes were extremely increased.