Change in soil macroporosity with land use and its effect on soil respiration

Soil macropores were intensively studied in the 1990s for their role in preferential flow. The renewed interest in macropores is their influence on soil organic carbon dynamics. A common method for measuring soil macropores is tension infiltration, which typically approximates them as a series of hydraulically isolated vertical cylinders. This approach contrasts with findings from imaging studies over the past decade, which suggest a more complex pore connectivity. We present an alternative method for estimating macroporosity based on the Green-Ampt infiltration model. In this approach, macropores are defined as pores that cannot retain water at matric potentials higher than -5 hPa. We applied this method to the long-term Rothamsted experiment that includes permanent grassland, arable land, and bare fallow plots. Macroporosity estimated using this in situ method was compared with values obtained directly from X-ray Computed Tomography. We also examined the influence of soil texture on macropore formation. To assess the effect of macropores on soil organic carbon dynamics, we measured CO₂ concentrations at the soil surface and at a depth of 15 cm to calculate CO₂ efflux. Our results show that although saturated hydraulic conductivity was similar across treatments, the macroporosity varied significantly. These structural differences had functional consequences: greater macroporosity was associated with higher CO₂ efflux. We provide a field-ready, scalable method for assessing macropore networks, which enhances the detection of management-induced changes in soil structure and function. This method offers new opportunities for advancing soil health monitoring under real-world conditions.