Abstract. In this paper, we present and analyze a novel global database of soil infiltration measurements, the Soil Water Infiltration Global (SWIG) database. In total, 5023 infiltration curves were collected across all continents in the SWIG database. These data were either provided and quality checked by the scientists who performed the experiments or they were digitized from published articles. Data from 54 different countries were included in the database with major contributions from Iran, China, and the USA. In addition to its extensive geographical coverage, the collected infiltration curves cover research from 1976 to late 2017. Basic information on measurement location and method, soil properties, and land use was gathered along with the infiltration data, making the database valuable for the development of pedotransfer functions (PTFs) for estimating soil hydraulic properties, for the evaluation of infiltration measurement methods, and for developing and validating infiltration models. Soil textural information (clay, silt, and sand content) is available for 3842 out of 5023 infiltration measurements (∼ 76%) covering nearly all soil USDA textural classes except for the sandy clay and silt classes. Information on land use is available for 76 % of the experimental sites with agricultural land use as the dominant type (∼ 40%). We are convinced that the SWIG database will allow for a better parameterization of the infiltration process in land surface models and for testing infiltration models. All collected data and related soil characteristics are provided online in *.xlsx and *.csv formats for reference, and we add a disclaimer that the database is for public domain use only and can be copied freely by referencing it. Supplementary data are available at https://doi.org/10.1594/PANGAEA.885492 (Rahmati et al., 2018). Data quality assessment is strongly advised prior to any use of this database. Finally, we would like to encourage scientists to extend and update the SWIG database by uploading new data to it.

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There is a need for improved knowledge of the limits to the available water range for root growth in the subsoil. The objective of this study was to recalculate the upper and lower limits of the least limiting water range (LLWR) concept by using respectively the air‐filled porosity (εa) at which 0.005 of the relative gas diffusivity (Ds/Do) is reached and readily available water (RAW). The refined upper limit estimates the variation in εa related to pore connectivity and the refined lower limit expresses the boundary at which plants suffer physiological water stress. This study was based on soil sampled in compaction trials on two sandy loam soils. Soil samples were taken from plots with no compaction (Control), and compaction with 78 kN (M8) and 58 kN (M6) wheel loads with multiple wheel passes. The soil cores were analyzed for εa, Ds/Do, bulk density (ρb) and penetration resistance (PR). Heavy farm machinery impact of M8 and M6 led to subsoil compaction up to depth of 0.5 to 0.7 m for the soils under study. The subsoil structure was affected by compaction across depths with the decrease in εa (∼33–46%) and Ds/Do (∼37–61%) and increase in ρb (∼4–8%) and PR (∼40–50%, at −100 hPa at 30‐cm depth). The refined LLWR showed a wider water range compared to the original approach. We anticipate that the refined LLWR well reflects the limiting soil physical conditions for root growth for the studied soils, but validation by combined soil physical and plant growth measurements is needed. Core Ideas Heavy traffic‐induced compaction narrows LLWR in the subsoil. Air permeability at critical limit of gas diffusivity take in pore organization. Using readily available water as the lower limit represents a drought stress boundary.

The "Visual Evaluation of Soil Structure" (VESS) is a method used primarily to evaluate the soil structural quality of Oxisols in Brazil and secondly for more specific research, consultancy, and teaching purposes. Since the methodology was never applied and compared with laboratory evaluations of physical properties of hydromorphic soils of the Pampa biome in the south of Brazil, this study evaluated the use of VESS as a visual indicator of the structure quality of a typic eutrophic Albaqualf soil under native grassland, crop-livestock integration, no-tillage, and conventional management systems. Experimental areas with these different management systems were subjected to visual (VESS) and laboratory evaluation of the soil structure. The laboratory evaluation was based on traditional methods and on measurements of bulk density, porosity, aggregate mean weight diameter, aggregate tensile strength (ATS), and total organic carbon (TOC). It was concluded that VESS was efficient in differentiating the management system. The management systems based on minimum soil disturbance and mulching with crop residues improved the soil quality, as evidenced by the VESS scores, bulk density, porosity, aggregation, and organic carbon. The TOC content was inversely related with ATS. The quality of a typic eutrophic Albaqualf was benefitted by organic matter in the surface layer.

The soil physical quality (SPQ) index S can provide inconsistent designations of SPQ and has a lack of consistency with other physical indicators for some soils. The aim of this study was to compare the suitability of S in identifying SPQ against 12 SPQ indicators, including water-release-related indicators, physical properties, and visual examinations. This study was conducted on medium-textured soil samples taken from tropical and temperate soils. Comparisons of SPQ class and relationships between indicators were used to judge the S SPQ designation. For the studied soils, S classified SPQ in the same way as other indicators when the condition of the soil was optimal or degraded but not when it was intermediate. This demonstrates that the proposed critical limits for S are not generally valid and do not apply for all soil conditions. Porosity parameters from the water release curve were more consistent indicators of SPQ than S. Our work also demonstrates that scores from visual examinations have at least similar resolution (P > 0.05) to the other indicators of SPQ evaluated. The use of S as an indicator to be considered as part of a minimum data set of indicators of SPQ assessment is less viable when other indicators such as bulk density, porosity, and visual examination are much more easily determined and more consistent than S. Therefore, it is too ambitious to consider that a unique indicator such as the S index could be used to evaluate SPQ as such.

Mechanical stresses from agricultural machinery affect subsoil layers, influencing pore systems and hence soil processes. The low resilience of the inflicted plastic deformation necessitates a better understanding of the impacts on soil functions and the risk of compromised soil ecosystem services. Soil samples were collected at 0.3‐, 0.5‐, 0.7‐, and 0.9‐m depths in a sandy loam subjected to repeated high wheel loads during 4 yr of slurry application at a water content close to field capacity. The 100‐cm3 soil samples were drained successively to matric potentials of –30 and –100 hPa, in which air permeability was measured via the Forchheimer approach, including estimation of apparent permeability (kapp) at four pneumatic pressure gradients. For all soil depths, the apparent permeability at 5 hPa pneumatic pressure for both control and compacted soil was significantly lower than the true Darcian permeability (kDarcy) derived from the relationship between the superficial air velocity and the pressure gradient. For high permeabilities, the ratio R (kapp/kDarcy) was generally lower than 0.3. This ratio was lower in compacted soil than in the control soil, significantly so for the 0.3‐m depth. For this depth, the decrease in R with increases in the average pore air velocity was more pronounced and a regression model explained more of the variation in data for compacted than for control soil. We consider that severe soil compaction may reduce the complexity of the subsoil pore system, closing a considerable part of the marginal pores branching from vertical (arterial) biopores. Core Ideas Darcian air permeability is underestimated if measured at large pressure gradients. The bias is stronger for compacted than for noncompacted subsoil. The bias in air permeability can be used to evaluate the soil pore system. Compaction is likely to increase the risk of preferential water flow.

Subsoil compaction caused by heavy traffic affects the soil pore system, resulting in long‐term damage to soil functions. The study contrasted two treatments from compaction experiments conducted at three different sites in Denmark: non‐trafficked control soil and soil subjected to four annual traffic events (2010–2013) with a wheel load of 58 to 78 kN. A cover crop of fodder radish (Raphanus sativus L.) was grown in half of the initial experimental plots after completion of the compaction treatments (2013 and onwards). In the spring of 2017, undisturbed soil cores were sampled at 0.3 and 0.5 m depth. The air‐filled porosity (εa), air permeability (ka) and gas diffusivity (Ds/Do) were quantified for samples equilibrated to –100 hPa matric potential. Soil pore structural indicators were estimated from the combination of εa, ka, and Ds/Do. The ratio of non‐Darcian to Darcian ka (R) was also used as a pore morphology indicator. For all sites and depths, compaction reduced εa, Ds/Do, ka‐Darcy, PO1 (ka‐Darcy/εa) and the effective radius ([(8ka‐Darcy)/Ds/Do]0.5) compared to control soil (p < 0.05). The Buckingham‐X variable relating Ds/Do and εa tended to be smaller for compacted soil, significantly for one of the sites. Compacted soils were also characterised by a significantly smaller R‐ratio at high levels of ka‐Darcy (> 32 μm2), but also by having a tendency for the R‐ratio to decrease rapidly with increasing pore air velocity compared to the control. The results reflect a compaction‐induced reduction in the number of marginal pores connected to large arterial pores, promoting a simple pore system formed by continuous vertical pores. The compaction effect was not affected by the cover crop. Neither natural recovery nor fodder radish‐induced mitigation of soil compaction was evident for the studied soils.

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