保护性耕作对华北平原土壤团聚体特征的影响

Effects of Conservation Tillage on Soil Aggregates in Huabei Plain,China

【目的】研究华北平原保护性耕作制度对土壤团聚数量、大小和稳定性的影响。【方法】本文采集了华北平原河北栾城试验站经过4年保护性耕作(旋耕和免耕)与传统耕作(翻耕)处理下原状土壤样品,测定了土壤容重、有机质和粘粒含量等物理性质,重点应用干筛和湿筛法分析了土壤团聚体数量、分布和分形维数。【结果】表层(0～5cm)土壤容重的大小顺序为免耕>旋耕>翻耕,免耕使表层土壤的容重显著增加;旋耕与翻耕的表层土壤容重差异不显著,但旋耕使10～20cm的土壤容重明显增加。干筛法分析表明,免耕处理下0～10cm土层大于0.25mm团聚体含量、平均重量直径(mean weight diameter,MWD)和几何平均直径(geometric mean diameter,GMD)均高于旋耕处理和翻耕处理,而旋耕与翻耕处理间没有显著的差异;湿筛法分析表明,土壤中的团聚体以非水稳性团聚体为主,水稳性团聚体的MWD和GMD大小顺序为免耕>旋耕>翻耕;在0～5cm土层内免耕处理的水稳性团聚体分形维数(D)最小,而旋耕处理下5～10cm的分形维数D值显著高于翻耕、免耕处理,说明旋耕使得该层内土壤团聚体的稳定性降低。【结论】免耕处理促进表层土壤团聚体的形成,并提高了其稳定性;旋耕和翻耕处理由于对土壤的强烈扰动,降低了耕作深度内土壤团聚体的团聚度和稳定性;在10～30cm3种耕作处理间没有显著差异。

【Objective】Tillage will greatly influence the aggregation and stability of soil aggregates.The paper studied the effects of conservation tillage on the soil characteristics.【Method】Soils from no-tillage（NT）,rotary tillage（RT）and conventional tillage（Moldboard tillage,CT）in plots of 4 years（2001-2005）at the Luancheng Research Station in Hebei Province were sampled.The aggregates amount,size distribution and fractal dimension were examined by dry and wet sieving methods.【Result】Results indicated that NT significantly increased the topsoil（0-5 cm）bulk density（BD）,while RT maintained lower BD.CT significantly increased at 10-20 cm.Dry sieving results showed that NT was higher in macro-aggregate content（R0.25）,mean weight diameter（MWD）and geometric mean diameter（GMD）than other treatments at 0-10 cm.RT showed no difference with CT.Wet sieving results showed that most of the aggregates are unstable,and the MWD and GMD of water-table aggregates showed the same trend：NT〉RT〉CT.At 0-5 cm,the fractal dimension（D）of water-stable aggregates under NT was lower than RT and CT;while at 5-10 cm,RT yielded highest D,and showed the worst stability.【Conclusion】NT increased the aggregation and the stability of soil aggregates,while due to intense disturbance,the aggregation and stability within tillage depth under RT and CT decreased.At 10-30 cm,there were no significant differences observed among the three tillage systems.