Quantification of soil structure via synchrotron X‐ray tomography after 22 years of fertilization

Abstract Applying fertilizers on a long‐term basis can promote the accumulation of soil organic matter and increase soil aggregation. The effects of organic and inorganic fertilizers on soil structure have manifested as different morphological characteristics for different soil types. To quantify the three‐dimensional (3D) pore structure of soil cores after long‐term fertilization, we collected cinnamon soil (Chromic Luvisol) aggregates and 2 cm × 2 cm × 2 cm soil cores from a long‐term fertilization field trial beginning in 1989. The treatment groups included no fertilization (CK), inorganic fertilization (NPK) and organic fertilization (OF). Synchrotron radiation‐based X‐ray microcomputer tomography (SR‐μCT) and digital image analysis were used to determine the soil core structure. The results showed that the long‐term practices of OF treatment increased the stability of wet aggregates. Combined visualization of the soil structure and morphological parameters consistently revealed that the soil pore systems under OF treatment were more connected and multilevel than those under the CK treatment after 22 years. The soil pore structures under the CK and NPK treatments were similar but significantly different from the structure under the OF treatment. Highlights Effect of long‐term organic and inorganic fertilization on soil structure was explored. SR‐μCT and digital image analysis techniques were applied to visualise the soil 3D pore structure. Long‐term application of organic fertilizers promoted the number of pores in soil aggregates. OF‐treated soil had more macropores and better continuity between the pores with longer path lengths.