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

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. K e y w o r d s: long-term fertilization, computed tomography, pore characteristics, air permeability, penetration resistance INTRODUCTION Soil pore characteristics determine solute transport, air and water fluxes, and affect plant water uptake and plant growth (Naveed et al., 2016; Pires et al., 2017). Thus, major research efforts have been devoted to predicting air permeability and saturated hydraulic conductivity under different soil pore structures (Luo et al., 2010; Zhang et al., 2019). Soil pores serve as planes of breakage along which aggregates form, and their sizes and spatial positions determine the micro-environmental conditions for crop root growth (Rabot et al., 2018). It has been shown that continuous macropores are beneficial for crop root growth in compacted soils as the macropores can provide spaces with low resistance and high concentrations of oxygen (Colombi et al., 2017). Therefore, soil pore structures such as macropores should be improved by using favourable agricultural management practices (Sainju et al., 2003). Soil macropores have been reported to be sensitive to organic fertilization treatment (Xu et al., 2018). It is generally believed that the addition of organic fertilizer increases the soil organic matter content and has a positive effect on soil aggregation and pore system development in a tilled cropping system (Pagliai et al., 2004; Dal Ferro et al., 2013). The increased biological activity resulting from manure application to the soil leads to more continuous biopores, which in turn contributes to increased macroporosity and pore connectivity (Naveed et al., 2014). Zhang © 2021 Institute of Agrophysics, Polish Academy of Sciences