Effects of different organic amendments on soil pore structure acquired by three‐dimensional investigation

Abstract The application of organic amendments is an important way to improve soil structure. However, the differences in soil pore properties after adding various organic materials are not fully available, which is important for selecting the most suitable material for soil improvement. In this study, soil pore structures in a field experiment amended with different organic materials (maize straw [MS], cattle manure, mixture of MS and cattle manure, biochar, woody peat, and polyacrylamide [PAM]) were determined by digital image analysis and three‐dimensional (3D) investigation, and their changes were quantitatively evaluated. The results showed that all organic material applications reduced the soil bulk density and increased the field capacity and water‐stable macroaggregate content. The 3D information about the soil pore structure showed that MS return was closely related to pore shape parameters. Soil treated with PAM had a low channel and throat number, long channel length and large throat area, all of which affect soil solute migration and crop root growth. A straw and organic fertiliser mixture changed the medium and large porosity (>500 μm) percentage from 1.1% to 9.7%, and the connected/isolated porosity ratio (C/I ratio) increased by 4.7 times. Taken together, our results indicate that the application of organic amendments can effectively improve the soil microstructure in fluvo‐aquic soils of the Huanghuaihai Plain in China, which is consistent with macroscopic physical properties such as bulk density and field capacity. PAM addition can promote the redistribution of air, water and nutrients in the soil. Straw returning can significantly affect the soil pore shape. Among all organic amendments, a straw and organic fertiliser mixture had the most obvious effects on the soil structure, especially on improving soil connectivity. Highlights Computed tomography and digital image processing used to visualise and quantify pore structure of soil treated with organic materials. Applications of various organic amendments reduced bulk density of fluvo‐aquic soil. Field capacity and water‐stable macroaggregates were increased. Straw and organic fertiliser improved soil porosity and connectivity and increased numbers of macropores.