Variable responses of soil pore structure to organic and inorganic fertilization in a Vertisol

Abstract

Soil pore structure may become highly variable under different fertilization regimes. This study aims to identify the impacts of long-term fertilization on the soil pore characteristics in a Vertisol and their relationships with water-holding capacity, air permeability and penetration resistance, using X-ray computed tomography. Intact soil cores were sampled from a long-term (37 years) continuous fertilization experiment including treatments with no fertilization (Control), inorganic fertilization, and organic fertilization. The basic soil properties, the three-dimensional characteristics of the macropores, water-holding capacity, air permeability and penetration resistance were all analysed. The results show that, in comparison with the control, the organic fertilization treatment resulted in increased total porosity, macroporosity and porosity with a diameter >1000 μm, this was probably due to the increased soil organic carbon content and aggregate stability. The inorganic fertilization treatment had a lower macropore connectivity, air permeability and higher penetration resistance relative to the control, a probable explanation is the decreased aggregate stability resulting from a large amount of dispersing ions in the inorganic fertilizers. Air permeability was positively correlated with macropore connectivity, while water-holding capacity and penetration resistance had no relationship with macropore characteristics. Our findings demonstrate that long-term organic fertilization can improve the macroporosity of Vertisol, while long-term inorganic fertilization has a detrimental effect on soil macropore connectivity.