No-tillage (NT) systems have been increasing during the last several decades. Development of a near-surface layer of laminar structure under NT has also been reported. The objectives of this work were to determine whether preferential connectivity of different pore size classes in two differently textured soils under NT exists and to propose a new index of pore connectivity based on water flux (Cw). The study was carried out at two sites in the Pampas Region of Argentina under long-term NT. Site 1 had a loamy A-horizon, and Site 2 had a sandy loam A-horizon. Undisturbed samples were extracted in vertical and horizontal directions within the first 8 cm of the soil. Saturated hydraulic conductivity (K s ), nearsaturated hydraulic conductivity (h: −50, −100, −200, −300, and −500 cm), pore size distribution from water retention curve, and total porosity were determined. The index of pore connectivity based on water flux, Cw, was developed as a ratio between K and pore volume for each pore size class. Site 1 showed laminar structure in the A-horizon, whereas Site 2 showed a blocky structure. We found a preferential connectivity in horizontal direction of macropores in Site 1. The index of pore connectivity was useful to assess the presence of preferential orientation of different pore size classes. In future studies, the connectivity of the different pore size classes should not be neglected.

Soil compaction has been recognized as a severe problem in mechanized agriculture and has an influence on many soil properties and processes. Yet, there are few studies on the long-term effects of soil compaction, and the development of soil compaction has been shown through a limited number of soil parameters. The objectives of this study were to evaluate the persistence of soil compaction effects (three traffic treatments: T0, without traffic; T3, three tractor passes; and T5, five tractor passes) on pore system configuration, through static and dynamic determinations; and to determine changes in soil pore orientation due to soil compaction through measurement of hydraulic conductivity of saturated soil in samples taken vertically and horizontally. Traffic led to persistent changes in all the dynamic indicators studied (saturated hydraulic conductivity, K 0 ; effective macro-and mesoporosity, ε ma and ε me ), with significantly lower values of K 0 , ε ma , and ε me in the T5 treatment. The static indicators of bulk density (BD), derived total porosity (TP), and total macroporosity (θ ma ) did not vary significantly among the treatments. This means that machine traffic did not produce persistent changes on these variables after two years. However, the orientation of the soil pore system was modified by traffic. Even in T0, there were greater changes in K 0 measured in the samples taken vertically than horizontally, which was more related to the presence of vertical biopores, and to isotropy of K 0 in the treatments with machine traffic. Overall, the results showed that dynamic indicators are more sensitive to the effects of compaction and that, in the future, static indicators should not be used as compaction indicators without being complemented by dynamic indicators.

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