Effects of organic and inorganic fertilization on soil aggregation in an Ultisol as characterized by synchrotron based X-ray micro-computed tomography

Abstract

Long-term fertilization practices generally improve soil aggregation through associated increases in organic matter over time. However, the influence of organic versus inorganic fertilization on aggregate structures may be quite different. In this paper, we aimed to quantify the three-dimensional (3D) microstructure of soil aggregates as influenced by different long-term fertilization practices. Soil aggregates with diameters of approximately 5mm were collected from an Ultisol with a long-term fertilization trial established in 1986. The treatments were no fertilizer (CK), chemical fertilizer (NPK), and chemical fertilizer plus organic manure (NPK+OM). The aggregate microstructure was determined with synchrotron based X-ray micro-computed tomography (SR-μCT) and digital image analysis techniques. Mean corn yields and soil organic carbon were the highest in NPK+OM, followed by NPK and then by CK. Aggregate stability was highest in NPK+OM, and lowest in NPK. The number of pores, number of pore throats, and number of paths between adjacent nodal pores were all significantly decreased by the NPK+OM treatment relative to the NPK and CK treatments. However, microstructural pore properties were mostly not different between NPK and CK treatments. This study demonstrates that organic fertilization can improve soil aggregation, while inorganic fertilization is ineffective, even after 25years. The different mechanisms by which organic and inorganic fertilization practices influence soil aggregation deserve further investigation.