耕作方式对黑土团聚体含量及特征的影响

【目的】研究保护性耕作对东北黑土团聚体粒级分布和稳定性的影响,为探索有利于东北黑土结构改善的耕作方式提供科学依据。【方法】以2001年(耕作试验开始前)和2008年(耕作试验实施7年后)吉林省中层黑土为对象,分析探讨了免耕(NT)、秋翻(MP)和垄作(RT)处理0—30cm深度的土壤水稳性团聚体、干团聚体特征和土壤结构稳定性。【结果】与2001年相比,2008年各处理(RT、MP、NT)1mm水稳性大团聚体含量在0—5cm表层中均有所增加,且除MP外均达到显著水平(P0.05),其中RT和NT增加幅度分别为2001年的4.78和3.38倍,且显著高于MP。0.25—0.053mm水稳性微团聚体变化趋势则与大团聚体相反。8mm干团聚体在0—10cm土层的相对数量表现为RTNTMP,且均高于2001年背景值,其中0—5cm土层RT显著高于MP及2001年背景值(P0.05)。0.25—1mm干团聚体RTNTMP2001年背景值,呈现与4mm干团聚体相反的变化趋势。2008年各处理团聚体平均重量直径(MWD)和0.25mm团聚体含量(R0.25)均比2001年有所提高,且湿筛法得到的结果远远低于干筛法,说明供试土壤的团聚体中水稳性团聚体比例很小。2008年3种耕作处理的土壤结构体破碎率和不稳定团粒指数(ELT)在各个土层均为MPNTRT,且除了MP处理5—20cm略高外,其它均低于2001年背景值。【结论】传统耕作不利于土壤大团聚体的增加和土壤结构的稳定,使土壤更易遭受风水侵蚀。保护性耕作,尤其垄作,促进了黑土稳定土壤结构体的形成,有利于土壤结构的改善。

Effects of Tillage on Soil Aggregates in Black Soils in Northeast China

【Objective】 In order to seek proper tillage methods for soil structure improvement, the impact of conservation tillage on soil aggregates size distribution and stability of a black soil in Northeast China was studied. 【Method】 Soil samples collected in 2001 prior tillage experiment and 2008 after tillage management implementing in place for 7 years were used. Tillage treatments include no-tillage (NT), moldboard plow (MP) and ridge tillage (RT). The contents and distribution of water stable and dry aggregates were determined for soils in 0-30 cm depth. 【Result】 Compared with the background values in 2001, water stable macro-aggregates increased in 0-5 cm in all tillage treatments in 2008, and was 4.78 and 3.38 times greater in RT and NT, respectively, compared with corresponding values in 2001, and all these were significantly higher than the values of MP soil in 2001 (P＜0.05). Water stable micro-aggregates (0.25-0.053 mm) showed an opposite tendency. The content of ＞8 mm dry aggregates followed the order of RT＞NT＞MP＞2001 at 0-10 cm depth, among those RT was significantly higher than MP (P＜0.05). Dry aggregates (0.25-1 mm) increased in the order of RT＜NT＜MP＜2001, displaying a pattern opposite to ＞4 mm ones. Mean weight diameter and ＞0.25 mm aggregates contents were greater in 2008 than in 2001, and those two values were far greater in dry-sieving than in wet-sieving which indicates water stable aggregates representing a small proportion of bulk soil. Structure deterioration rate and index of unstable aggregates in 2008 decreased in the order of MP＞NT＞RT at 0-30 cm depth, and the values were apparently less than that in 2001 except in 5-20 cm MP soil. 【Conclusion】 Consequently, conventional tillage is undesirable for soil structure characters while conservation tillage, especially RT could promote the formation of stable macro-aggregates and contribute to black soil structure improvement in Northeast China.