Abstract:

【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.

Key words: conservation tillage, soil aggregates, mean weight diameter, soil structure