The Influence of Straw Returning to the Field on the Soil Agglomeration Structure and Carbon Sequestration Effect of Meadows

This study aimed to explore the effects of different straw return methods on the distribution and stability of soil aggregates, as well as the organic carbon components and carbon sequestration effect in meadow soil, so as to provide the theoretical and practical basis for improving soil aggregate structure and enhancing carbon sequestration potential.

Based on an 11-year long-term field experiment, the treatments were no straw returning (CK), full no-tillage with straw mulching (SNT), half no-tillage with straw mulching (NT), full annual incorporation of straw (S1), and full biennial incorporation of straw (S2).

Compared with the CK treatment, the SNT treatment significantly increased soil organic carbon content in the 0-40 cm soil layer by 2.5% to 6.6%. Straw returning could increase the content of active carbon components (easily oxidized organic carbon and microbial biomass carbon) in the 0-40 cm soil layer to varying degrees. Among them, the S1 treatment significantly increased the easily oxidized organic carbon content in the 0-40 cm soil layer from 15.4% to 20.1%, and the NT treatment significantly increased the microbial biomass carbon content in the 0-40 cm soil layer from16.0% to 17.6%. The SNT treatment significantly increased the easily oxidized organic carbon and microbial biomass carbon content in the 0-40 cm soil layer, with increases of 53.6% to 54.1% and 34.6% to 57.2%, respectively. Compared with the CK treatment, the S2 treatment significantly increased the percentage of water-stable macroaggregates (>0.25 mm) in the 0-20 cm soil layer and improved the distribution of aggregates of different sizes. The content of 3-5 mm and 0.5-1 mm aggregates increased significantly by 16.8% and 49.0%, respectively. The S1 treatment and NT treatment significantly increased the percentage of water-stable macroaggregates (>0.25 mm) in the 20-40 cm soil layer. The content of >5 mm aggregates in the S1 treatment increased significantly by 10.3%, and the content of 3-5 mm aggregates in the NT treatment increased significantly by 25.7%. The content of easily oxidized organic carbon in the surface soil was significantly positively correlated with the percentage of >0.25 mm macroaggregates. The effects of different straw returning methods on the content of easily oxidizable organic carbon in each particle size aggregate were different. The SNT treatment and the S1 treatment significantly increased the content of easily oxidizable organic carbon in each particle size aggregate. Among them, the SNT treatment increased the content by 9.5%-15.9% in the 0-20 cm soil layer and by 9.1%-23.9% in the 20-40 cm soil layer, while the S1 treatment increased the content by 12.7%-23.2% in the 0-20 cm soil layer and by 14.8%-19.4% in the 20-40 cm soil layer.

Different straw returning methods could increase the soil organic carbon content and the content of active carbon components in the 0-40 cm soil layer to varying degrees, and improve the distribution of aggregate size classes. Among them, full amount no-tillage and straw mulching returning was more conducive to increasing soil organic carbon, easily oxidized organic carbon and microbial biomass carbon content, and promoting the formation of easily oxidized organic carbon in aggregates to enhance soil carbon sequestration potential.