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Changes in soil physical properties due to compaction are a major concern in agricultural production and modeling of soil water movement and plant growth. The objectives of this study were to measure water infiltration under different compaction levels and to characterize the effects of compaction on the soil's porosity and its associated water-conducting properties. On a silt loam soil, relative to a control, four levels of subsurface compaction were induced: loosening and light, medium, and heavy compaction. Infiltration characteristics were measured in situ using tension infiltrometers. Near-saturated conductivities were calculated using Wooding's equation and further analyzed to derive the hydraulically effective macro-and mesoporosities and the flow-weighted mean pore radii. The data were also used for parameterization ofthe van Genuchten-Mualem model by inverse parameter estimation. A high susceptibility to the applied compaction was found: the saturated hydraulic conductivity of the heavily compacted soil was 81% less than that ofthe loosened soil. This soil property may be used as a proxy for compaction-induced changes in hydraulic characteristics. Increasing compaction also decreased the number of hydraulically effective macropores, reduced the flow-weighted mean pore radius, and the ttyj-parameter ofthe van Genuchten-Mualem model. Our findings give indirect evidence for two main efFects ofthe applied compaction.First, the reduced saturated hydraulic conductivity might be due to distortion of structural flow paths, reducing the connectivity and hydraulic effectiveness of many macropores. Second, compaction rearranged the pore space, resulting in more water-conducting mesopores.

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As soils under permanent pasture and grasslands have large topsoil carbon (C) stocks, the scope to sequester additional C may be limited. However, because C in pasture/grassland soils declines with depth, there may be potential to sequester additional C in the subsoil. Data from 247 continuous pasture sites in New Zealand (representing five major soil Orders and ~80% of the grassland area) showed that, on average, the 0.15–0.30 m layer contained 25–34 t ha−1 less C than the top 0.15 m. High‐production grazed pastures require periodic renewal (re‐seeding) every 7–14 years to maintain productivity. Our objective was to assess whether a one‐time pasture renewal, involving full inversion tillage (FIT) to a depth of 0.30 m, has potential to increase C storage by burying C‐rich topsoil and bringing low‐C subsoil to the surface where C inputs from pasture production are greatest. Data from the 247 pasture sites were used to model changes in C stocks following FIT pasture renewal by predicting (1) the C accumulation in the new 0–0.15 m layer and (2) the decomposition of buried‐C in the new 0.15–0.30 m layer. In the 20 years following FIT pasture renewal, soil C was predicted to increase by an average of 7.3–10.3 (Sedimentary soils) and 9.6–12.7 t C ha−1 (Allophanic soils), depending on the assumptions applied. Adoption of FIT for pasture renewal across all suitable soils (2.0–2.6 M ha) in New Zealand was predicted to sequester ~20–36 Mt C, sufficient to offset 9.6–17.5% of the country's cumulative greenhouse gas emissions from agriculture over 20 years at the current rate of emissions. Given that grasslands account for ~70% of global agricultural land, FIT renewal of pastures or grassland could offer a significant opportunity to sequester soil C and offset greenhouse gas emissions.