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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

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