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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

16 Pags., 4 Tabls., 4 Figs. The definitive version is available at: http://onlinelibrary.wiley.com/journal/10.1002/(ISSN)1099-145X ; The Ebro River valley in Northeast Spain experiences regularly strong west-northwest winds that are locally known as cierzo. When the cierzo blows, wind erosion may potentially occur on unprotected agricultural lands. In this paper the first results of field measurements of soil characteristics and saltation transport in the Ebro River valley near Zaragoza are presented. An experiment was conducted on a silt loam soil in the summers of 1996 and 1997. Two plots of 135×180 m were both equipped with a meteorology tower, three saltiphones (acoustic sediment sensors) and ten sediment catchers. The plots were different with respect to tillage practices. One plot received mouldboard ploughing followed by a pass of a compacting roller (conventional tillage—CT), whereas the other plot only received chisel ploughing (reduced tillage—RT). Soil characterizations indicated that soil erodibility was significantly higher in the CT plots than in the RT plots. Consequently, no significant saltation transport was observed in the RT plots during both seasons. In the CT plot, four saltation events were recorded during the 1996 season and nine events during the 1997 season. Most events were preceded by rainfall during the previous one or two days, which reduced saltation transport significantly. It is concluded that the occurrence of wind erosion in the Ebro River valley depends on the timing and type of tillage, distribution of rainfall and soil-surface crusting. ; The WELSONS project is funded by the European Union under Contract No. ENV4‐CT95‐0182. ; Peer reviewed

The definitive version is available at: http://www.sciencedirect.com/science/journal/11610301 ; In Central Aragón (NE Spain), where strong and dry winds are frequent all year round, fallow lands are susceptible to wind erosion due to insufficient crop residues on the surface and loose, finely divided soils by multiple tillage operations. Effects of conventional tillage (mouldboard ploughing followed by a compacting roller) and reduced tillage (chisel ploughing) on soil surface properties affecting wind erosion were studied during three experimental campaigns in a dryland field of Central Aragón. Reduced tillage provided higher soil protection than conventional tillage through a lower wind erodible fraction of soil surface (on average, 10% less) and a significantly higher percentage of soil cover with crop residues and clods (30% higher). Random roughness was also higher after reduced tillage than after conventional tillage (15% vs. 4%). These results indicate that reduced tillage can be an effective soil management practice for wind erosion prevention during the fallow period in semiarid Aragón. The study shows, likewise, that significant changes in soil aggregate size distribution associated with wind erosion processes may occur in short periods of time. Thus, temporal variability of soil surface properties, including crust and clods stability, needs to be considered in wind erosion research in agricultural soils. ; This work was supported by the WELSONS project funded by the European Union (Contract No. ENV4-CT95-0182). The first author is grateful to the Spanish Ministry of Education and Culture for her PNFPI contract. ; 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://www.ametsoc.org/ ; During the second phase of the EFEDA experiment (ECHIVAL Field Experiment in a Desertification Threatened Area), the spatial variability of the soil water retention and hydraulic conductivity characteristics of layers 2-12 and 17-27 cm depth was characterized. A simplified method, based on particle size distribution and simple infiltration tests was used. It provided these characteristics at the nodes of a 1 km grid over 10x10 km2 around the town of Tomelloso (Castilla- La Mancha, Spain). A total number of 78 sample points were used to address the problem of soil surface properties variability and its consequences on the monthly and annual water balance. The SiSPAT (Simple Soil Plant Atmosphere Transfer model) 1-D Soil-Vegetation-Atmosphere Transfer (SVAT) model was run with a one-year climatic forcing for the 78 soil profiles until equilibrium was reached. As no runoff was generated, the spatial variability of the water budget components only concerned soil evaporation, transpiration and deep drainage. It was found that i) the choice of the type of boundary condition at the bottom of the soil profile was greatly influencing the final variability, ii) the variability of transpiration was the largest in situations of water stress for the vegetation, iii) soil evaporation was the most sensitive component when plants were well supplied with water. Various aggregation methods of soil surface parameters (use of the arithmetic mean, median of the parameters or parameters associated to the average soil texture of the Clapp and Hornberger (1978) classification) were assessed. The use of median parameters in a single 1-D simulation was found to provide the best agreement with the average of the 78 simulations performed for each grid cell using locally measured soil properties. The use of average soil texture parameters led to a significant bias, especially in the case of water stress. ; This study was funded by the European Union in the context of the ECHIVAL Experiment in a Threatened Desertification Area (EFEDA) project (EPOCH-CT 90-0030 and EV5V-CT93-0272). ; Peer reviewed

In semiarid Mediterranean agroecosystems, low and erratic annual rainfall together with the widespread use of mouldboard ploughing (conventional tillage, CT), as the main traditional tillage practice, has led to a depletion of soil organic matter (SOM) and with increases in CO2 emissions from soil to the atmosphere. In this study, we evaluated the viability of conservation tillage: RT, reduced tillage (chisel and cultivator ploughing) and, especially, NT (no-tillage) to reduce short-term (from 0 to 48 h after a tillage operation) and mid-term (from 0 h to several days since tillage operation) tillage-induced CO2 emissions. The study was conducted in three long-term tillage experiments located at different sites of the Ebro river valley (NE Spain) across a precipitation gradient. Soils were classified as: Fluventic Xerocrept, Typic Xerofluvent and Xerollic Calciorthid. Soil temperature and water content were also measured in order to determine their influence on tillage-induced CO2 fluxes. The majority of the CO2 flux measured immediately after tillage ranged from 0.17 to 6 g CO2 m−2 h−1 and was from 3 to 15 times greater than the flux before tillage operations, except in NT where soil CO2 flux was low and steady during the whole study period. Mid-term CO2 emission showed a different trend depending on the time of the year in which tillage was implemented. Microclimatic soil conditions (soil temperature and water content) had little impact on soil CO2 emission following tillage. In the semiarid Mediterranean agroecosystems studied, NT had low short-term soil CO2 efflux compared with other soil tillage systems (e.g., conventional and reduced tillage) and therefore can be recommended to better manage C in soil. ; This research was supported by the Comisión Interministerial de Ciencia y Tecnología of Spain (Grants AGL 2001-2238-C02-01 and AGL 2004-07763-C02-02) and the European Union (FEDER funds). The first author was awarded a FPI fellowship by the Spanish Ministry of Science and Education.

Long-term tillage negatively affects soil aggregation, but little is known about the short-term effects of tillage. We investigated the effects of intensive tillage (moldboard plowing) and conservation tillage (chisel plowing) on aggregate breakage during tillage in a long-term study located in the semiarid Ebro river valley (NE Spain). The type of tillage resulted in different soil aggregate distributions. In the 0–5-cm and 5–10-cm soil layers, chisel plowing decreased dry mean weight diameter (DMWD) 29% and 35%, respectively, while moldboard plowing decreased DMWD by only 2% and 16%, respectively. The decrease in DMWD was mainly due to breaking of large aggregates ranging (2–8 mm) into small aggregates (<0.5 mm). Tillage method had no effect on water stability of 1–2 mm aggregates. The differences in DMWD demonstrate that the choice of the tillage implement can be a key factor in improving soil management and productivity. The surprising result that aggregate breakdown was greater with chisel than moldboard plowing needs further research to determine the mechanisms controlling aggregate breaking during tillage. ; This research was supported by the Comisión Interministerial de Ciencia y Tecnología of Spain (Grants AGL2001-2238-CO2-01, AGL 2004-07763-C02-02, AGL2007-66320-CO2-02/AGR) and the European Union (FEDER funds).

Losses of soil organic carbon (SOC) have contributed to CO2 emissions from soils to the atmosphere and to global climate change. We hypothesized that in semiarid agroecosystems of the Mediterranean region, a shift from the traditional management system (including conventional tillage [CT] and a cereal–fallow rotation) to a more conservative system, including no-till (NT) and continuous cropping, could reduce CO2 emissions during the cropping season. Thus, in this study, we studied the effects of tillage and cropping systems on C inputs and soil CO2 fluxes during three cropping seasons at three different sites in the Ebro River valley (northeast Spain). Carbon inputs ranged from 650 to 6000 kg ha–1 and seasonal average CO2 flux ranged from 0.10 to 1.76 g CO2 m–2 h–1. Differences in rainfall led to marked differences in C inputs and soil fluxes among growing seasons. Although differences among tillage treatments were weak, CO2 fluxes under NT were always lower. Intensification of cropping systems led to an increase in C input. A move from CT to NT together with cropping intensification is suitable to increase C inputs and to reduce soil CO2 fluxes in semiarid Mediterranean agroecosystems. ; This research was supported by the Comisión Interministerial de Ciencia y Tecnología of Spain (Grants AGL2001-2238-CO2-01 and AGL 2004-07763-C02-02) and the European Union (FEDER funds). The first author was awarded a FPI fellowship by the Spanish Ministry of Science and Education.

37 Pags.- 6 Tabls.- 3 Figs. The definitive version is available at: http://www.sciencedirect.com/science/journal/01671987 ; The inherent complexity of soil organic matter (SOM) and its stabilization processes make suitable the identification of SOM fractions that reflect the management-induced changes in soil organic carbon (SOC) dynamics. This is of special interest in semiarid regions where the capacity of soil for agricultural production is limited. This study aims to evaluate the effect of different tillage and soil management practices on the distribution of C among SOM fractions and determine the influence of soil texture on the protection of SOC in a semiarid Mediterranean region (Aragon, NE Spain). Under on-farm conditions, pairs of adjacent fields under long-term no tillage (NT) and conventional tillage (CT) were compared in five different cereal production areas. In all cases, a nearby undisturbed soil under native vegetation (NAT) was included. Results indicate that the two isolated mineral-associated OM (Min) fractions, d-Min and μagg-Min (outside and within stable microaggregates, respectively), constituted the main part of total SOC (mean contributions of 54 and 26%, respectively) and were not consistently affected by soil management. Soil clay was a determinant factor for d-Min-C and total SOC (r2 = 0.60–0.70; P NT > CT). The highest differences between NT and CT corresponded to fPOM at the soil surface where this fraction was 1.2–3 times higher under NT. Higher soil stratification ratios in NT, always >2 for the POM fractions, indicate an improvement in soil quality with long-term NT adoption in this semiarid Mediterranean region. ; 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 was awarded a FPI Fellowship by the Spanish Ministry of Science and Innovation. ; Peer reviewed

29 Pags., 4 Figs., 5 Tabls. The definitive version is available at: http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1475-2743 ; Soil organic carbon (SOC) plays an essential role in the sustainability of natural and agricultural systems. The identification of sensitive SOC fractions can be crucial for an understanding of SOC dynamics and stabilization. The objective of this study was to assess the effect of long-term no-tillage (NT) on SOC content and its distribution between particulate organic matter (POM) and mineral-associated organic matter (Min) fractions in five different cereal production areas of Aragon (north-east Spain). The study was conducted under on-farm conditions where pairs of adjacent fields under NT and conventional tillage (CT) were compared. An undisturbed soil nearby under native vegetation (NAT) was included. The results indicate that SOC was significantly affected by tillage in the first 5 cm with the greatest concentrations found in NT (1.5–43% more than in CT). Below 40 cm, SOC under NT decreased (20–40%) to values similar or less than those under CT. However, the stratification ratio (SR) never reached the threshold value of 2. The POM-C fraction, disproportionate to its small contribution to total SOC (10–30%), was greatly affected by soil management. The pronounced stratification in this fraction (SR>2 in NT) and its usefulness for differentiating the study sites in terms of response to NT make POM-C a good indicator of changes in soil management under the study conditions. Results from this on-farm study indicate that NT can be recommended as an alternative strategy to increase organic carbon at the soil surface in the cereal production areas of Aragon and in other analogous areas. ; 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 a FPI Fellowship by the Spanish Ministry of Science and Innovation. ; Peer reviewed

10 Pag., 1 Fig. The definitive version is available at: http://sjss.universia.net/ ; [EN] This paper assesses the long-term effect of no-tillage (NT) on soil organic carbon (OC) content and its distribution among different organic matter fractions in rainfed agrosystems of Aragón (NE Spain). Adjacent fields of NT, conventional tillage (CT) and natural soils (NAT) were compared in three different cereal production areas. In the soil surface, the higher OC content found in the NAT soils was due to the particulate organic matter. In the case of agricultural soils, in general, the fractions responsible for the OC increase under NT were the fine particulate organic matter and the mineral-associated organic matter occluded within stable microaggregates. ; [ES] En este trabajo se evalúa el efecto a largo plazo del no laboreo (NT) en el contenido de carbono orgánico del suelo (OC) y su distribución en diferentes fracciones de materia orgánica en agrosistemas de secano en Aragón (NE España). En tres diferentes zonas cerealistas se compararon campos adyacentes de NT, laboreo tradicional (CT) y suelo natural (NAT). En la superficie del suelo, el mayor contenido en CO encontrado en los suelos NAT se debió a la materia orgánica particulada. En el caso de los suelos agrícolas las fracciones responsables del incremento de OC en NL fueron, en general, la materia orgánica particulada fina y la fracción órgano-mineral de los microagregados estables. ; [PO] Este trabalho avalia o efeito a longo prazo do plantio direto (NT) no conteúdo de carbono orgânico no solo (OC) e a sua distribuição em diferentes frações da matéria orgânica em sistemas agrícolas de sequeiro em Aragon (NE Espanha). Campos adjacentes do NT, plantio convencional (CT) e solos naturais (NAT) foram comparados em três diferentes áreas de produção de cereais. Na superfície do solo, o maior teor de OC encontrado nos solos NAT deveu-se à matéria orgânica particulada. No caso dos solos agrícolas, as frações responsáveis pelo aumento de OC em NL foram, em geral, à matéria orgânica particulada fina e a fração organo-mineral de microagregados estáveis. ; This research was supported by the Comisión Interministerial de Ciencia y Tecnología of Spain (Grants AGL2007-66320-CO2- 02/AGR and AGL2010-22050-CO3-02/AGR) and the European Union (FEDER funds). The first author 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

Losses of soil organic carbon (SOC) have contributed to CO2 emissions from soils to the atmosphere and to global climate change. We hypothesized that in semiarid agroecosystems of the Mediterranean region, a shift from the traditional management system (including conventional tillage [CT] and a cereal–fallow rotation) to a more conservative system, including no-till (NT) and continuous cropping, could reduce CO2 emissions during the cropping season. Thus, in this study, we studied the effects of tillage and cropping systems on C inputs and soil CO2 fluxes during three cropping seasons at three different sites in the Ebro River valley (northeast Spain). Carbon inputs ranged from 650 to 6000 kg ha–1 and seasonal average CO2 flux ranged from 0.10 to 1.76 g CO2 m–2 h–1. Differences in rainfall led to marked differences in C inputs and soil fluxes among growing seasons. Although differences among tillage treatments were weak, CO2 fluxes under NT were always lower. Intensification of cropping systems led to an increase in C input. A move from CT to NT together with cropping intensification is suitable to increase C inputs and to reduce soil CO2 fluxes in semiarid Mediterranean agroecosystems. ; This research was supported by the Comisión Interministerial de Ciencia y Tecnología of Spain (Grants AGL2001-2238-CO2-01 and AGL 2004-07763-C02-02) and the European Union (FEDER funds). J. Álvaro-Fuentes was awarded an FPI fellowship by the Spanish Ministry of Science and Education. ; 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

The final version is available at: http://www.sciencedirect.com/science/journal/01671987 ; Long-term tillage negatively affects soil aggregation, but little is known about the short-term effects of tillage. We investigated the effects of intensive tillage (moldboard plowing) and conservation tillage (chisel plowing) on aggregate breakage during tillage in a long-term study located in the semiarid Ebro river valley (NE Spain). The type of tillage resulted in different soil aggregate distributions. In the 0–5-cm and 5–10-cm soil layers, chisel plowing decreased dry mean weight diameter (DMWD) 29% and 35%, respectively, while moldboard plowing decreased DMWD by only 2% and 16%, respectively. The decrease in DMWD was mainly due to breaking of large aggregates ranging (2–8 mm) into small aggregates (<0.5 mm). Tillage method had no effect on water stability of 1–2 mm aggregates. The differences in DMWD demonstrate that the choice of the tillage implement can be a key factor in improving soil management and productivity. The surprising result that aggregate breakdown was greater with chisel than moldboard plowing needs further research to determine the mechanisms controlling aggregate breaking during tillage. ; This research was supported by the Comisión Interministerial de Ciencia y Tecnología of Spain (Grants AGL2001-2238-CO2-01, AGL 2004-07763-C02-02, AGL2007-66320-CO2-02/AGR) and the European Union (FEDER funds). The first author was awarded a FPI fellowship by the Spanish Ministry of Science and Education. ; Peer reviewed