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Aims The surface crust formed by the drop impact of rainfall and/or irrigation is a prevalent characteristic in many Mediterranean soils. However, the temporal variation of soil hydraulic properties induced by surface crust during the high-frequency irrigation has rarely been investigated. Methods Beerkan infiltration tests in conjunction with the BEST method were used to investigate the effects of surface crusting on the spatio-temporal variation of saturated soil hydraulic conductivity (Ks, mm s−1), sorptivity (S, mm s−0.5), mean pore size (r, mm), number of effective pores per unit area (N, m−2) in Agramunt, NE Spain. Results In response to autumn tillage, intensive tillage (IT) increased Ks and S due to higher r and N, but both declined after 60 days. Reduced tillage (RT), maintained comparable Ks and S values, despite having a lower N value. After the spring tillage, both IT and RT developed crusted layers, resulting in decreased Ks, S and N. Long-term no-tillage (NT) showed an increasing trend of Ks and S over time, except for the last sampling. Spatial variation (i.e., between the rows, B-row vs. within the row of crops, W-row) of Ks and S was found, and non-crusted soils (W-row) had consistently higher Ks and S than crusted soils (B-row). Conclusions Conservation tillage i.e., RT and NT improve the surface soil structure and reduce the risk of crust development. Surface cover by crops may help to prevent crust formation within the row of crops, improving soil hydraulic conductivity.

<p>Water flow throughout the soil allows and regulates life on the Earth's surface. Knowing where this flow mainly takes place (preferential flow) is critical i) to measure it appropriately, ii) to take advantage of it for a more efficient use of water. Soil management has great impact on soil hydrological properties and can have an effect at catchment scale, while knowing within plot variability can improve flow estimations at plot level. On a 22-year-old experiment comparing intensive (IT) and no-tillage (NT), soil hydrological properties were determined within (W-row) and between (B-row) crop rows several times along two cropping years (2018-19 and 2019-20) on undisturbed soil cores. Tillage significantly influenced soil water retention being higher under IT than NT in the wet range above -10 cm soil matric potential. The cause was a larger volume of mesopores (1000 to 300 µm in diameter) in IT. Despite that, hydraulic conductivity was significantly higher in NT in this range, especially because mesopores in NT revealed greater pore continuity than in IT. No differences in soil hydraulic conductivity were found at lower soil matric potentials. These results suggest that, although IT increases soil porosity creating new pores regularly, these pores are less interconnected than the long-standing pores created in NT by the roots and fauna activity. The lower hydraulic conductivity in IT can reduce infiltration and increase runoff losses resulting in less water available for crops.  The position with respect to the crop row (W-row or B-row), did not have an impact on soil water retention but on soil hydraulic conductivity, that was significantly higher under W-row than B-row above -10 cm H<sub>2</sub>O soil water potential. Although the volume of pores of different size classes did not differ between both row positions, continuity of macropores (>1000 µm) was significantly higher under W-row than B-row and tended to be higher W-row also for the other pore classes. The effect of the sowing slot, the growth of the plant roots, and the protective effect of the plant cover itself can explain the preferential flow pathway found W-row. The differences between flow regimes under different tillage systems found at the small scale highlight the importance of considering the site-specific management impacts on soil structure and pore geometry, as these will affect hydrological flow processes at the catchment scale. Differences between positions with respect to the plant row need to be considered to properly characterize hydrological flow phenomena in soils, even under the same management practices.</p>

<p>In arid and semi-arid regions, high intensity rainfall and/or irrigation water drop leads to development of surface crust, and it has the potential to alter surface soil hydraulic properties while also accelerating runoff and erosion. However, the temporal variation of soil hydraulic properties under irrigated conditions due to surface crust under different soil management practices has rarely been studied. On a long-term tillage field experiment (26 years), in Agramunt, NE Spain, a study was carried out using Beerkan infiltration tests in conjunction with the inverse optimization algorithms of  the BEST method (Beerkan Estimation of Soil Transfer parameters) to investigate the effects of surface crusting on the spatio-temporal variation of saturated soil hydraulic conductivity (<em>K<sub>s</sub></em>, mm s<sup>-1</sup>), sorptivity (<em>S</em>, mm s<sup>-0.5</sup>), mean pore size (<em>r</em>, mm) and number of hydraulically active pores per unit area<em> </em>(<em>N</em>, m<sup>-2</sup>). Three tillage systems (intensive tillage, IT, reduced tillage, RT; and no-tillage, NT), two crop sequences (short fallow-maize, FM; and legume-maize, LM) and two positions (within the row of crops, W-row, and between the rows of crops, B-row) were assessed to evaluate the crusting effect on the above-mentioned soil hydro-physical properties. In response to autumn tillage, IT increased <em>K<sub>s </sub></em>and <em>S</em> due to higher <em>r</em> and <em>N</em>, but both declined after 60 days. RT, on the other hand, exhibited resilient to crust formation and despite having a lower <em>N</em> value, maintained comparable <em>K<sub>s</sub></em> and <em>S</em> values. After the spring tillage, its effect was immediately lost because of high-frequency water application, and both IT and RT developed crusted layers, resulting in decreased <em>K<sub>s</sub></em>, <em>S </em>and <em>N</em>. Long-term NT was resilient to form crust and an increasing trend of <em>K<sub>s</sub></em> and <em>S </em>was observed over time, except for the last sampling. Spatial variation (i.e., B-row vs. W-row) of<em> K<sub>s</sub></em> and <em>S</em> was found because of crusting, and independently of crop sequence, non-crusted soils (W-row) had consistently higher <em>K<sub>s</sub></em> (0.021 vs. 0.009 mm s<sup>-1</sup>)<sup></sup>and <em>S</em> (0.65 vs. 0.38 mm s<sup>-0.5</sup>) than crusted soils (B-row) due to their lower bulk density and <em>N</em>. According to the findings of this study, conservation agriculture practices such as RT and NT improve the stability of surface soil structure and steadily reduce the risk of crust development. Further, surface cover by crops may help to prevent crust formation within the row of crops, improving soil hydraulic conductivity. This enhanced water flow path must not be neglected when measuring infiltration.</p>

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