季节性冻融对苹果梨园机械稳定性团聚体的影响

Effects of Seasonal Freezing and Thawing on Mechanical Stability of Soil Aggregates in Apple-pear Orchards

季节性冻融作用(季节交替)对土壤团聚体的影响是最直接和有效的。由于延边地区气候和地理位置的特殊性,果园土壤经历着反复冻融,使得土壤机械稳定性团聚体分布及粒级变化具有较强的地域特征。采用沙维诺夫法对季节性冻融前后苹果梨园土壤团聚体进行机械筛分并计算其平均重量直径、几何平均直径和粒径分形维数,探究季节性冻融前后各指标的变化,以期为指导苹果梨园土壤的改良提供理论支持。结果表明:季节性冻融后苹果梨园0~20 cm土层土壤团聚体变化明显,20~60 cm土层变化不明显;0~20 cm土层经冻融后大团聚体含量增加、小团聚体含量减少;20~60 cm土层冻融后大团聚体和小团聚体含量均减少、中等大小团聚体含量增加。栽植年限40 a及以下果园冻融后变化明显,40 a以上果园不明显。季节性冻融后苹果梨园0~20 cm土层土壤团聚体重量直径和几何直径显著增加,分形维数有变小的趋势。荒地与苹果梨园趋势相反,季节性冻融后,大团聚体(> 7 mm)显著减少,土壤团聚体重量直径和几何直径显著降低。

Seasonal freezing-thawing(seasonal alternation) has the most direct and effective effect on soil aggregates.Because of the particular climate and geographical location in Yanbian area, orchard soil experienced the repeated freezing-thawing cycling, which leads to the strong regional characteristics of soil mechanical stability aggregates and their particle sizes. Soil aggregates in apple-pear orchards before and after the seasonal freezing-thawing were mechanically screened by the Savinov method, and their mean weight diameter(MWD), geometric mean diameter(GMD)and fractal dimension(FD) were calculated. The changes of each index before and after seasonal freezing-thawing were explored in order to provide theoretical support for guiding soil improvement in apple-pear orchards. The soil aggregates changed obviously at 0-20 cm soil layer, but did not change significantly at 20-60 cm soil layer of apple-pear orchard after the seasonal freezing-thawing. The percentage of large aggregates was increased and that of small aggregates decreased after the freezing-thawing at 0-20 cm soil layer. The freezing-thawing decreased the percentage of large aggregates and small aggregates, and increased that of medium-sized aggregates at 20-60 cm soil layer. After freezing-thawing, the change of orchards planted for 40 years or less was obvious, but it was not obvious for orchards planted for more than 40 years. After seasonal freezing-thawing, the mean weight and GMD of soil aggregates were increased significantly, and the FD tended to decrease at 0-20 cm soil layer of apple-pear orchard.After seasonal freezing-thawing, the percentage of large aggregates(> 7 mm) was decreased significantly, and the MWD and GMD of soil aggregates were decreased significantly in the wasteland.