Abstract: 【Objective】To clarify the effects of long-term no-tillage and mulching measures on soil aggregate structure and organic carbon content in Weibei dry plateau farmland, and to explore suitable tillage measures to improve the regional soil.【Method】On the basis of continuous 16-year field positioning experiments, traditional tillage (CT), no-tillage and no mulch (NT), no-tillage + straw mulch (NS), no-tillage + plastic film mulching (NP), no-tillage + A total of 5 field management measures, including straw + plastic film mulching (NSP), were used. The 0-40 cm ring knife and profile soil samples were collected during the spring corn harvest in October 2019, and the bulk density, aggregate particle size distribution and organic carbon content were determined.【Result】(1) No-tillage and mulching measures (NT, NP, NS and NSP) affected the bulk density and aggregate size distribution of Heilu soil. No-tillage and mulching measures both increased the soil bulk density of the plough layer, of which 0-10 cm increased significantly (6.8%-17.8%). The changes of bulk density and porosity of the plough layer were opposite to those of the plough layer. The proportion of micro-aggregates was significantly reduced, which promoted the transformation of micro-aggregates into macro-aggregates. The weight percentage of aggregates of each particle size in the plough layer (0-20 cm) is distributed as follows: larger aggregates (0.25-2 mm) > large aggregates (>2 mm) > micro aggregates (0.053-0.25 mm) > powder. The clay fraction (<0.053 mm), the larger aggregates and silty clay fractions in the plow bottom layer (20-40 cm) were significantly higher than the macroaggregates and microaggregates. (2) Under no-tillage and mulching measures, the organic carbon content increased with the increase of aggregate particle size. In the 0-40 cm soil layer, the organic carbon content of the aggregates of each particle size in the NT treatment was significantly lower than that in the CT treatment, while the NS and NSP treatments were significantly higher than those in the CT treatment. (3) The particle size distribution of aggregates is the dominant factor causing the change of the nutrient contribution rate of aggregates. The total organic carbon accumulation in the plough layer is dominated by aggregates >0.25 mm, and the plough layer is mainly composed of silty clay components and organic carbon in larger aggregates main. 【Conclusion】Long-term no-tillage and mulching measures promote the transformation of micro-aggregates into macro-aggregates in the plough layer. Compared with traditional tillage, no-tillage and plastic film mulching decreased the organic carbon content of aggregates of various particle sizes in Heilong soil and in the plough layer, respectively. However, no-tillage mulching (NS, NP and NSP) increased the organic carbon content of aggregates of each particle size compared with no mulching. Straw mulching alone had the best effect, and significantly improved the bulk density and aggregate particle size distribution, which was the best treatment.

Key words: no-tillage, coated, straw mulching, organic carbon, aggregate size, Weibei dry plateau