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5 Pags.- 5 Figs.- 2 Tabls. The definitive version is available at: http://www.sciencedirect.com/science/journal/00221694 ; Many gypsiferous soils occur in arid lands, where the water retention capacity of the soil is vital to plant life and crop production. This study investigated the effect of gypsum content on the gravimetric soil water retention curve (WRC). We analyzed calcium carbonate equivalent (CCE), equivalent gypsum content (EG), soil organic carbon content (SOC), and electrical conductivity of 43 samples collected from various horizons in soils in the Ebro Valley, NE Spain. The WRC of the fine earth was determined using the pressure-plate method (pressure heads = 0, −33, −100, −200, −500, and −1500 kPa), and the gravimetric water retention curves were fitted to the unimodal van Genuchten function. Soil gypsum content had a significant effect on water retention. Soils that had high gypsum content made WRC with higher water retention at near saturation conditions, and steeper WRC slopes. The EG threshold at which gypsum content had an effect on WRC was about 40%, and EG was positively and negatively correlated with the α and n parameters of the WRC, respectively. ; This article is a result of the research project AGL2012-40100 funded by the Spanish Government. ; Peer reviewed

Knowledge of soil water conductive porosity is of paramount importance for understanding the water and solute movement in soil. The objective of this study was to describe and evaluate an alternative pore index, i.e., the representative mean pore radius for two consecutive soil water tensions (lambda(Delta psi)), for characterizing the water-transmitting macro- and mesoporosity of soil. The hydraulic conductivity (K) and related hydraulic parameters were measured using a tension disk infiltrometer at -14, -4, -1, and 0 cm water pressure heads at a soil depth of 2 cm on a long-term conservation tillage experiment (after 9 yr of trial) under conventional tillage (CT), reduced tillage (RT), and no-tillage (NT) treatments. The soil was loam (Xerollic Calciorthid). The measurements were performed within the first half of a 16- to 18-mo-long fallow period. Unlike the model based on the classical capillary rise theory, which assumes no differences between measurement sites (e.g., tillage treatments) for the corresponding equivalent pore radius (CD) for macro- and mesopores, significant differences in lambda(Delta psi) values for macro- and mesopores were found between the three tillage systems tested. The number of water-transmitting macro- and mesopores per unit area estimated by means of the capillary rise approach was significantly greater than that calculated using the lambda(Delta psi) pore index. Although significantly higher values of lambda(Delta psi) for both macro- and mesopores were observed under NT a significantly lower near-saturation K was found under NT than CT and RT treatments due to the lower density of water-transmitting macro- and mesopores. ; This research was supported by the Comisión Interministerial de Ciencia y Tecnología of Spain (Grants no. AGF98-0261-C02-02 and AGL 2001-2238-CO2-01 and PNFPI predoctoral fellowship and research contract awarded to the first author) and the European Union (FEDER funds). ; Peer reviewed

The definitive version is available at: http://www.sciencedirect.com/science/journal/01671987 ; There is limited information on the effects of tillage practices on soil hydraulic properties, especially changes with time. The objective of this study was to evaluate on a long-term field experiment the influence of conventional tillage (CT), reduced tillage (RT) and no-tillage (NT) on the dynamics of soil hydraulic properties over 3 consecutive 16–18 month fallow periods. Surface measurements of soil dry bulk density (ρb), soil hydraulic conductivity (K(ψ)) at −14, −4, −1 and 0 cm pressure heads using a tension disc infiltrometer, and derived hydraulic parameters (pore size, number of pores per unit of area and water-transmission porosity) calculated using the Poiseuille's Law were taken on four different dates over the fallow period, namely, before and immediately after primary tillage, after post-tillage rains and at the end of fallow. Under consolidated structured soil conditions, NT plots presented the most compacted topsoil layer when compared with CT and RT. Soil hydraulic conductivity under NT was, for the entire range of pressure head applied, significantly lower (P < 0.05) than that measured for CT and RT. However, NT showed the largest mean macropore size (0.99, 0.95 and 2.08 mm for CT, RT and NT, respectively; P < 0.05) but the significantly lowest number of water-conducting pores per unit area (74.1, 118.5 and 1.4 macropores per m2 for CT, RT and NT, respectively; P < 0.05). Overall, water flow was mainly regulated by macropores even though they represented a small fraction of total soil porosity. No significant differences in hydraulic properties were found between CT and RT. In the short term, tillage operations significantly increased K (P < 0.05) for the entire range of pressure head applied, which was likely a result of an increase in water-conducting mesopores despite a decrease in estimated mesopore diameter. Soil reconsolidation following post-tillage rains reduced K at a rate that increased with the intensity of the rainfall events. ; This research was supported by the Comisión Interministerial de Ciencia y Tecnología of Spain (Grants no. AGF98-0261-C02-02 and AGL 2001-2238-CO2-01 and PNFPI predoctoral fellowship and research contract awarded to the first author) and the European Union (FEDER funds). ; Peer reviewed

9 Pags., 3 Figs., 2 Tabls. The definitive version is available at: http://www.sciencedirect.com/science/journal/18780296/19/supp/C ; This paper describes a new method (NSQE) to estimate soil hydraulic properties (sorptivity, S, and hydraulic conductivity, K) from full-time cumulative infiltration curves. The technique relies on an inverse procedure involving the quasi-exact equation of Haverkamp et al. (1994). The numerical resolution is described and the sensitivity of the method is theoretically evaluated, showing that the accuracy of the estimates depends on the measured infiltration time. A new procedure to detect and remove the effect of the contact sand layer on the cumulative infiltration curve is also given. The method was subsequently compared to the differentiated linearization procedure (DL), which calculate K and S from the simplified Haverkamp et al. (1994) equation, valid only for short to medium times. A total of 264 infiltration measurements performed with a 10cm diameter disc under different soil conditions were used. Compared to the DL procedure, field measurements showed that the NSQE method allowed better estimates of soil hydraulic properties, independently on the infiltration noise and the presence of contact sand layer. Overall, although comparable S values were estimated with both methods, the longer infiltration times allowed by the proposed method made this procedure more accurate estimations of K. In conclusion, the NSQE method have shown to be a significant advance to accurate estimate of the soil hydraulic properties form the transient water flow. ; This research was supported by the Ministerio de Ciencia e Innovación of Spain (Grant AGL2010- 22050-C03-02) and by the Aragón Regional Government and La Caixa (Grant 2012/GA LC 074). ; Peer reviewed

The definitive version is available at: http://www.sciencedirect.com/science/journal/01671987 ; In Central Aragon, winter cereal is sown in the autumn (November–December), commonly after a 16–18 months fallow period aimed at conserving soil water. This paper uses the Simple Soil–Plant–Atmosphere Transfer (SiSPAT) model, in conjunction with field data, to study the effect of long fallowing on the soil water balance under three tillage management systems (conventional tillage, CT; reduced tillage, RT; and no-tillage, NT). This was on the assumption that soil properties would remain unchanged during the entire fallow season. Once the model was validated with data obtained before primary tillage implementation, the differences between simulated and observed soil water losses for the CT and RT treatments could be interpreted as the direct effect of the soil tillage system. The model was calibrated and validated in a long-term tillage experiment using data from three contrasting long-fallow seasons over the period 1999–2002, where special attention was paid to predicting soil hydraulic properties in the pre-tillage conditions. The capacity of the model to simulate the soil water balance and its components over long fallowing was demonstrated. Both the fallow rainfall pattern and the tillage management system affected the soil water budget and components predicted by the model. The model predicted that about 81% of fallow seasonal rainfall is lost by evaporation in long-fallow periods with both a dry autumn in the first year of fallow and a rainfall above normal in spring. Whereas, when the fallow season is characterised by a wet autumn during the first year of fallow the model predicted a decrease in soil water evaporation and an increase in water storage and deep drainage components. In this case, the predicted water lost by evaporation was higher under NT (64%) than under RT (56%) and CT (44%). The comparison between measured and simulated soil water loss showed that the practice of tillage decreased soil water conservation in the short term. The long-term analysis of the soil water balance showed that, in fallow periods with a wet autumn during the first year of fallow, the soil water loss measured under CT and RT was moderately greater than that predicted by the model. ; This research was supported by the Comisión Interministerial de Ciencia y Tecnología of Spain (grants AGF98-0261-CO2-02 and AGL2001-2238-CO2-01 and PNFPI pre-doctoral fellowship awarded to the first author) and the European Union (FEDER funds). ; Peer reviewed

33 Pags., 4 Tabls., 4 Figs. The definitive version is available at: http://www.sciencedirect.com/science/journal/03418162 ; Due to particular soil and climate conditions and inappropriate agricultural practices, Aragon (NE Spain) is a region prone to land degradation by water erosion. For this reason, the adoption of conservation tillage systems has been encouraged as an alternative to preserve soil and water in this region. However, little information concerning soils on which these techniques are applied is available. The main objectives of this study were to assess the effect of long-term no tillage (NT) on wateraggregate stability in five different cereal production areas of Aragon and identify the main mechanisms involved on aggregate breakdown. The study was conducted under on-farm conditions where pairs of adjacent fields under NT and conventional tillage (CT) were compared. In all cases, a nearby undisturbed soil under native vegetation was included. Soils were slightly to highly calcareous with medium textures ranging from sandy loam to silty clay loam. Results indicate that NT increased surface aggregate stability with respect to CT systems through lower soil disturbance and higher organic carbon (OC) content at the soil surface (0–5 cm depth). Slaking was the dominant disaggregation process of the cultivated soils, representing 40–80% of total soil disruption, and was strongly and negatively affected by aggregate-associated OC. This soil property together with the silt content (weak and positive effect) explained more than 80% of the slaking variation. Swelling and clay dispersion were less frequent processes and their occurrence seemed to be associated with high silt and CaCO3 contents. This study shows that, under the rainfed conditions of semiarid Aragon, NT reduces the susceptibility of soil surface to crusting and water erosion as compared to CT systems. ; This research was supported by the Comisión Interministerial de Ciencia y Tecnología of Spain (Grants AGL2010-22050-CO3-02/AGR and AGL2007-66320-C02-02/AGR) and the European Union (FEDER funds). N. Blanco-Moure was awarded with a FPI fellowship by the Spanish Ministry of Science and Innovation. ; Peer reviewed

20 Pag., 4 Figs., 1 Tabl. The definitive version is available at: http://www.sciencedirect.com/science/journal/03783774 ; Pasture productivity depends on soil hydro-physical properties, which in turn are deeply affected by livestock grazing. However, the comparative response of different soil types, and particularly gypseous soil types, to grazing has hardly been studied before. This paper compares the effect of grazing on the soil hydro-physical properties of silty gypseous (Gy) and non-gypseous (NGy) soils located in a semi-arid region (Middle Ebro Valley, NE, Spain). Two different soil managements were selected: ungrazed natural shrubland (N) and grazed shrubland (GR) soils. The gypsum, CaCO3 and organic matter content (OM), soil texture, soil bulk density ( b), penetration resistance (PR), saturated sorptivity (S), hydraulic conductivity (K), and the water retention curve (WRC) for undisturbed soil samples from 1 to 10 cm depth soil layer were measured. The b and PR in NGy soils were significantly higher than those observed in the Gy ones. Soil compaction due to grazing treatment tended to increase b and decrease the K and S values. While no differences in PR were observed in the Gy soils between grazing treatments, the PR measured in the NGy soils under GR was significantly higher than the corresponding values observed under N. Differences in K and S between GR and N treatments were only significant (p < 0.05) in NGy soils, where K and S values under the N treatment were almost four times greater than the corresponding values measured under GR. Overall, no differences in the WRCs were observed between soil types and grazing treatments. While the WRCs of NGy soils were not significantly affected by the grazing treatment, Gy soils under N treatment present a significantly higher level of soil macropores than under GR treatment. The hydro-physical features of Gy soils tended to be less affected by grazing than those of the NGy soils. These results suggest that livestock grazing, in both Gy and NGy soils, has a negative effect on the physical soil properties, which should be taken into account by land managers of these semi-arid regions where silty gypseous and non-gypseous areas coexist. ; This research was supported by Aragón regional government and La Caixa (Grants: GA-LC020/2010; GA-LC-010/2008) and the CSIC (Grant: PIE-200930I145). ; Peer reviewed

20 Pags.- 2 Tabls.- 8 Figs. The definitive version is available at: http://ascelibrary.org/journal/jidedh ; This work presents and applies a new methodology to find the optimal topography of a surface irrigation field, achieving a theoretically uniform surface irrigation. For any variant on surface irrigation (basin, border or furrow, with open or blocked end), the method's result is a particular curved topographical shape of a field. This shape distributes water evenly over the field so that distribution uniformity is theoretically 100% and deep percolation disappears. The methodology was applied to two theoretical cases: (1) a one-dimensional blocked-end field, and (2) a two-dimensional square field with corner inflow. For each case, the methodology reached a particular topography in which distribution uniformity was near 100%. To put this methodology into practice, the optimized topography (which has a curved shape) can be fitted with two or more different slopes. An example is shown in which a real field was laser-levelled with two consecutive slopes to fit the optimized topography; it previously was calculated with the methodology presented in this paper. The irrigation was evaluated before and after the optimization. The results indicated an increase of distribution uniformity from 82 to 96%. The topographic optimization methodology offers new information about topography influence on irrigation performance indicators. The main practical conclusion is that this method can be useful to determine the best slope, set of slopes or curved shape when levelling any field for surface irrigation. ; This work was supported by the Government of Arag ´on (Spain) and the European Social Fund (European Union). ; Peer reviewed

sta comunicación presenta varios avances realizados en la t écnica de infiltrometría de tensión. (i) Nuevas bases de disco que permiten medidas de infiltración sin utilizar arena de contacto (disco de base adaptable) o sobre cobertura vegetal (base con forma de sombrero). (ii) Estimación de la conductividad hidráulica (K) y sorptividad (S) del suelo a partir de la solución numérica de la ecuación cuasi- analítica de la curva de infiltración acumulada 3D (NSQE). Los resultados muestran que los prototipos presentados permiten medir de forma satisfactoria la curva de infiltración acumulada de agua en el suelo. Paralelamente, el método NSQE aplicado sobre 400 medidas de infiltración ha re sultado ser robusto y ofrece estimaciones más precisas de K y S. ; This research was supported by the Ministerio de Ciencia e Innovación of Spain (grant AGL2010-22050-C03-02) and by the Aragón regional government and La Caixa (Grants: GA-LC020/2010; GA-LC006/2008; 2012/ GA LC 074). T ; Peer Reviewed

19 Pags. The definitive version, with 2 Tabls. and 6 Figs., is available at: http://onlinelibrary.wiley.com/journal/10.1002/(ISSN)1099-1085 ; The correct use of the tension disc infiltrometer requires the membrane of the disc base to be completely in contact with the soil surface. To achieve this contact, a thick layer of sand is commonly placed between the soil surface and the disc base. This paper presents an alternative disc (MDB), which, by incorporating a malleable membrane, allows direct infiltration measurements without using a contact sand layer. Infiltration curves obtained with this new design in a soil under three different tillage management treatments were compared with the corresponding curves obtained with a conventional disc (CDB) that uses a contact sand layer. The cumulative infiltration curves measured with CDB were analysed by the differentiated linearization (DL) method, and the corresponding curves obtained with MDB were analysed using both the DL and the cumulative linearization (CL) models. The values of hydraulic conductivity (K0) and sorptivity (S0) estimated with CDB were also compared with those obtained with MDB. Finally, the cumulative infiltration curves measured with CDB and MDB were compared with the corresponding modelled function for the respective K0 and S0 values calculated with the CL and DL models. The results show that, compared with CDB without a contact sand layer, MDB allows complete soil surface wetting even when non-smoothed soil surfaces are used. The CDB, which yielded average K0 values 18% lower than those estimated with MDB, gave the highest values of standard error for the hydraulic parameters calculated. Furthermore, the subjective method employed in the CDB-DL technique, which requires the first points of the differential infiltration line corresponding to the sand layer to be manually removed, introduces additional uncertainties in estimating S0 and K0. Comparison between the modelled and measured infiltration curves demonstrates that the DL or CL methods applied to MDB gave excellent estimates of S0 and K0. ; This research was supported by the Ministerio de Ciencia e Innovación of Spain (grant AGL2010-22050-C03-02) and by the Aragón regional government and La Caixa (grant GA-LC020/2010). ; Peer reviewed

El pdf del artículo es la versión pre-print. ; Tensile strength (TS) of soil aggregates is recognized as a useful parameter to detect structural changes associated with soil management. Although conservation tillage has been encouraged as a management alternative to preserve soil and water resources in semiarid Aragon (NE Spain), little information concerning soils on which these techniques are applied is available for this region. The main objective of this study was to assess the effect of long-term no tillage (NT) on TS, rupture energy (E) and organiccarbon (OC) of soil surface aggregates (0–5 cm depth) in five different cereal production areas of Aragon. In four of the sites, the study was conducted under on-farm conditions where pairs of adjacent fields under NT and conventional tillage (CT) were compared. In the last site, the study was carried out in research plots from a long-term tillage experiment where a third tillage treatment was also considered (reduced tillage). In all cases, a nearby undisturbed soil under native vegetation was included. Results indicate that NT reduced aggregate TS and E with respect to CT systems through lower soil disturbance and higher OC content. Aggregate size (16–8, 8–4, 4–2 and 2–1 mm in diameter) and aggregate-associated OC explained 70–80% of the variation in TS and E. Strength properties varied with OC in quadratic way with minimum values at about 20 g kg− 1 of OC. This behavior can be explained by the significant interactions found between clay and OC in such a way that in the soils with the highest values of clay and OC, aggregate strength increased considerably. This study shows that, under the rainfed conditions of semiarid Aragon, NT improves soil physical conditions by reducing aggregatestrength at the soil surface. This means, for example, that NT could provide a more favorable environment for seedling emergence and root growth than the traditional practices in the area. ; This research was supported by the Comisión Interministerial de Ciencia y Tecnología of Spain (grants AGL2010-22050-CO3-02/AGR and AGL2007-66320-C02-02/AGR) and the European Union (FEDER funds). N. Blanco-Moure was awarded with a FPI fellowship by the Spanish Ministry of Science and Innovation. ; Peer reviewed

The definitive version is available at: http://vzj.scijournals.org/ ; Time Domain Reflectometry (TDR) is a valuable technique that allows simultaneous estimation of the apparent permittivity (a) and the bulk electrical conductivity (a). However, in highly conductive media the signal is completely attenuated which precludes permittivity measurements. This paper shows that a can be estimated in conductive media by applying the long-time TDR waveform analysis to a TDR probe partially insulated with a high-dielectric coating. Four 10-cm-long three-rod TDR probes with identical geometry but different percentages of rod-coating were tested: an uncoated sensor (P0) and probes with 50% (P50), 75% (P75) and 95% (P95) of the rod-length, respectively, coated with an insulator with a relative permittivity (r) equal to 32.3. A good relationship (r2 = 0.99) was found between the a estimated, if possible, with P0 immersed in several conductive and nonconductive media and the corresponding values estimated with P50, P75 and P95. The cell constant value (m-1) for P0 (5.10), P50 (9.60), P75 (16.92) and P95 (51.31), which were experimentally determined in different NaCl-water solutions, were on average 10% greater than the corresponding values calculated using a numerical model. The results show that, for a values ranging between 0.4 and 0.75 S m-1, simultaneous measurements of a and a were only possible using the partially coated probes. A good correlation was found between the a estimated with P0 inserted in different soil columns wetted with highly saline solutions (i.e. a > 0.2 S m-1) and those values estimated with P50, P75 and P95 (R2 = 0.96, RMSE = 1.08 and SD = 0.38). For a values lower than 0.2 S m-1 the accuracy of the partially coated TDR probes for estimations of a decreases as increases the percentage of the rod-coating, with errors up to 292% when a determined by P95 was compared to that estimated by P0. ; This research was supported by the Comisión Interministerial de Ciencia y Tecnología of Spain (grant AGL2007-66320-CO2-02/AGR) and the European Union (FEDER funds). ; Peer reviewed

45 Pags.- 4 Tabls.- 5 Figs. The definitive version is available at: http://www.sciencedirect.com/science/journal/00221694 ; Based on the analysis of Haverkamp et al. (1994), this paper presents a new technique to estimate the soil hydraulic properties (sorptivity, S, and hydraulic conductivity, K) from the full-time cumulative infiltration curves. The proposed method, which will be named as the Numerical Solution of the Haverkamp equation (NSH), was validated on 12 synthetic soils simulated with HYDRUS-3D. The K values used to simulate the synthetic curves were compared to those estimated with the NSH method. A procedure to detect and remove the effect of the contact sand layer on the cumulative infiltration curve was also developed. A sensitivity analysis was performed using the water level measurement as uncertainty source and the procedure was evaluated considering different infiltration times and data noise (e.g. air-bubbling in the infiltrometer). The good correlation between the K used in HYDRUS-3D to model the infiltration curves and those obtained by the NSH method (R2 =0.98) indicates this technique is robust enough to estimate the soil hydraulic conductivity from complete infiltration curves. The numerical procedure to detect and remove the influence of the contact sand layer on the K and S estimates resulted to be robust and efficient. A negative effect of the curve infiltration noise on the K estimate was observed. The results showed that infiltration time was an important factor to estimate K. Smaller values of K or lower uncertainty required longer infiltration times. In a second step, the technique was tested in field conditions on 266 different soils at saturation conditions, using a 10 cm diameter disc infiltrometer. The NSH method was compared to the standard differentiated linearization procedure (DL), which estimates the hydraulic parameters using the simplified Haverkamp et al. (1994) equation, valid only for short to medium times. Compared to DL, NSH was considerably less affected by the infiltration bubbling and the contact sand layer, and allowed more robust estimates of K and S. Although comparable S values were obtained with both methods, the NSH technique, which is not limited to short times, resulted in more accurate and robust estimates for K. This paper demonstrates the NSH method is a significant advance to estimate of the soil hydraulic properties from the transient water flow. ; This research was supported by the Ministerio de Ciencia e Innovación of Spain (grant AGL2010-22050-C03-02) and by the Aragón regional government and La Caixa (Grants: 2012/ GA LC 074). ; Peer reviewed

15 Pags., 3 Tabls., 6 Figs. the definitive version is available at: http://link.springer.com/journal/10021 ; Water redistribution from bare soil to vegetation patches is a key feature of semi-arid ecosystems, and is responsible for their patchy vegetation patterns. The magnitude of water redistribution depends on the properties of the bare soil (which determine the amount of water run-off) and the capacity of vegetation patches to trap water run-on. We examined the relationships between plant spatial patterns, water infiltration into bare soil, and plant community composition in semi-arid sites with different hydro-physical properties (silty and gypseous soils) in NE Spain. We also studied the effect of two stressors, aridity and grazing, on water infiltration and plant spatial patterns. Our results indicate a negative correlation of bare soil sorptivity (the capacity to absorb water by capillarity) and vegetation aggregation. There was a strong positive correlation between perennial grass cover and the spatial aggregation of vegetation, but aggregation was not associated with positive associations of different plant types. The aggregation of vegetation was positively correlated with species richness and the overall extent of vegetation cover. Grazing reduced water infiltration into silty soils, which are prone to compaction. In contrast, soil crust affected the hydrology of gypseous soils, especially in the most arid sites, where grazing increased infiltration, reducing surface sealing due to breaking of the soil crust. Together, our results suggest that biotic and abiotic factors affect the hydro-physical properties of soils in the semi-arid ecosystems of NE Spain, which is linked to the plant communities through the spatial distribution of plants. ; The projects GA-LC-010/2008, GA-LC-020/2010 (from Aragon regional government), and CGL2011-27259 (from the Spanish Ministry of Science and Innovation co-financed with FEDER) provided financial support for this study. ; Peer reviewed

The final version of this article is available at: http://www.sciencedirect.com/science/journal/01671987 ; This paper presents a new type of pressure cell associated with a zigzag-shaped time domain reflectometry (TDR) probe for determining the soil-water retention (θ(ψ)) curve of disturbed thin soil samples. The pressure cell, designed for pressures ranging between 0 and −500 kPa, consisted of a zigzag copper rod (150-mm long, 2 mm in diameter) vertically installed in a clear plastic cylinder (60-mm high, 50 mm in internal diameter) with six vertical copper rods (60-mm long, 2 mm in diameter) arranged around the inner wall of the plastic cylinder. The cylinder was closed at the base with a nylon cloth and placed on a porous ceramic disc. The inner rod and the six-rod grille of the cell were connected respectively to the inner and outer conductors of a coaxial cable. The results showed that the correlation between the apparent dielectric constant measured with a standard three-rod TDR probe and the zigzag-shaped TDR probe, both immersed in five different non-conductive fluids, was excellent (R2 = 0.99). On the other hand, the volumetric water content measured with the TDR probe of the pressure cell filled up with sand, 2-mm sieved loam and clay-loam soils was highly correlated to the corresponding values calculated from the gravimetric water content and the soil bulk density (R2 = 0.97; RMSE = 2.32 × 10−2). The parameters of the θ(ψ) curves measured for these three different soils with the TDR-pressure cell were within the range of values found in the literature. The cell was also used to study the θ(ψ) changes of a 2–4-mm sample of loam soil aggregates after a slow and a fast-wetting process. While negligible changes in both the soil structure and θ(ψ) were observed following slow wetting, fast wetting resulted in disintegration of aggregates and drastic changes in the shape of the θ(ψ) curve. ; This research was supported by the Comisión Interministerial de Ciencia y Tecnología of Spain (grants AGL2004-07763-C02-02 and AGL2007-66320-CO2-02/AGR) and the European Union (FEDER funds). ; Peer reviewed