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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. [ABSTRACT FROM AUTHOR]

The water retention curve (θ(ψ)), which defines the relationship between soil volumetric water content (θ) and matric potential (ψ), is of paramount importance in characterizing the hydraulic behaviour of soils. However, few methods are so far available for estimating θ(ψ) in undisturbed soil samples. We present a new design of TDR-pressure cell (TDR-Cell) for estimating θ(ψ) in undisturbed soil samples. The TDR-Cell consists of a 50-mm-long and 50-mm internal diameter stainless steel cylinder (which constitutes the outer frame of a coaxial line) attached to a porous ceramic disc and closed at the ends with two aluminium lids. A 49-mm-long and 3-mm-diameter stainless steel rod, which runs longitudinally through the centre of the cylinder, constitutes the inner rod of a coaxial TDR probe. The TDR-Cell was used to determine the θ(ψ) curves of a packed sand and seven undisturbed soil samples from three profiles of agricultural soils. These θ(ψ) curves were subsequently compared to those obtained from the corresponding 2-mm sieved soils using the pressure plate method. Measurements of bulk electrical conductivity, σa, as a function of the water content, σa(θ), of the undisturbed soil samples were also performed. An excellent correlation ( R2 = 0·988) was found between the θ values measured by TDR on the different undisturbed soils and the corresponding θ obtained from the soil gravimetric water content. A typical bimodal θ(ψ) function was found for most of the undisturbed soil samples. Comparison between the θ(ψ) curves measured with the TDR-Cell and those obtained from the 2-mm sieved soils showed that the pressure plate method overestimates θ at low ψ values. The σa(θ) relationship was well described by a simple power expression ( R2 > 0·95), in which the power factor, defined as tortuosity, ranged between 1·18 and 3·75. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In semiarid agroecosystems of the Ebro valley (NE Spain) soils are characterized by tow soil organic matter (SOM) and a weak structure. In this study we investigated the individual and combined effect of tillage system (no-tillage, NT; reduced tillage, RT; conventional tillage, CT) and cropping system (barley-fallow rotation at the Peflaflor site, PN-BF and continuous barley at the Peñaflor site, PN-BB) on soil organic carbon (SOC) storage as well as the physical protection of SOM fractions by soil aggregates in three long-term experimental sites. In both cropping systems, total SOC content was more than 30% higher in NT compared with CT in the 0- to 5-cm depth. The suppression of fallowing in the PN-BB cropping system led to a greater SOC stabilization only in NT. In all the three sites, greater proportion of water-stable macroaggregates (>250 pm) was found under NT than under CT in the 0- to 5-cm depth. Macroaggregate organic C concentration (250-2000 pm) was greater in NT compared with CT in the BB cropping system, but did not differ with tillage treatment in the PN-BF rotation. Greater proportion of microaggregates within macroaggregates in NT compared with CT was only found in the Agramunt site (AG). However, greater C stabilized inside these microaggregates was observed in AG, Selvanera site (SV), and PN-BB in the 0- to 5-cm depth. The results of this study demonstrate that in the semiarid Mediterranean agroecosystems of the Ebro valley, the adoption of NT together with the suppression of long-fallowing period can significantly increase the amount of SOC stabilized in the soil surface and improve soil structure and aggregation. [ABSTRACT FROM AUTHOR]

Time domain reflectometiy (TDR) is a technique that allows simultaneous estimates of apparent permittivity (ϵa) and hence volumetric water content (θ) and bulk electrical conductivity (σa). Difficulties arise for θ and σa determination, however, when uncoated TDR probes (UP) are used in highly conductive media. This work shows that σa can be estimated in highly conductive media using a TDR probe coated with a high-dielectric insulator (CP). To this end, the Dalton method for σa estimations was applied to a 10-cm-long three-rod TDR probe insulated with a 0.2-mm-thick epoxy-ceramic composite coating with a relative permittivity, ϵr, of 32.3. This method was calibrated on different NaCl-water solutions (0-15 dS m-1) and compared with the standard long-time TDR method for σa estimations using an UP. The method was subsequently used for determining σa in four different soils with different values of θ and σa (0-6 dS m-1) and again compared with the standard TDR procedure. The low error (RMSE = 1.5) for the comparison between the ϵa measured with the CP and that calculated with the analytical solution for coaxial probes indicates that the CP is accurate enough for ϵa estimations. For σa values <4 dS m-1, the UP allows determinations of ϵa and the most accurate estimations of σa using the standard TDR method (R2 = 0.99). For higher σa values, however, estimations of ϵa were only possible using the CP, where σa was satisfactorily determined (R2 = 0.99) using the Dalton method. To this end, a previous calibration between the real and the apparent bulk electrical conductivity estimated with the CP was required. [ABSTRACT FROM AUTHOR]

Under semiarid conditions, soil quality and productivity can be improved by enhancing soil organic matter content by means of alternative management practices. In this study, we evaluated the feasibility of no-till (NT) and cropping intensification as alternative soil practices to increase soil organic C (SOC). At the same time, we studied the influence of these management practices on two SOC fractions (particulate organic matter C, POM-C, and the mineral-associated C, Min-C), in semiarid agroecosystems of the Ebro River valley. Soil samples were collected from five soil layers (0-5-, 5-10-, 10-20-, 20-30-, 30-40-cm depth) during July 2005 at three long-term tillage experiments located at different sites in the Ebro River valley (northeast Spain). Soil bulk density, SOC concentration and content, SOC stratification ratio, POM-C, and Min-C were measured. Higher soil bulk density was observed under NT than under reduced tillage (RT), subsoil tillage (ST), or conventional tillage (CT). At the soil surface (0-5-cm depth), the highest total SOC concentration, POM-C, and Min-C were measured under NT, followed by RT, ST, and CT, respectively. In the whole soil profile (0-40 cm), similarly, slightly greater SOC content was measured under NT than under CT with the exception of the Selvanera site, where deep subsoil tillage combined with moldboard plowing accumulated more SOC than NT. In semiarid Mediterranean agro-ecosystems where CT consists in moldboard plowing, NT is a viable management practice to increase SOC. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Pseudomonas species causing pith necrosis symptoms on tomato and pepper collected in different areas of Argentina were identified as Pseudomonas corrugata , P. viridiflava and Pseudomonas spp. Their diversity was analysed and compared with reference strains on the basis of their phenotypic characteristics, copper and antibiotic sensitivity tests, serology, pathogenicity, DNA fingerprinting and restriction fragment length polymorphism (RFLP) analysis of a 16S rRNA gene fragment. All P. corrugata strains tested were copper-resistant while P. viridiflava strains were more variable. Numerical analysis of phenotypic data showed that all P. corrugata strains formed a single phenon that clustered at a level of about 93%, while all the P. viridiflava strains clustered in a separated phenon at a level of 94%. Genomic analysis by repetitive (rep)-PCR and 16S rRNA-RFLP fingerprinting and serological analysis showed that the two species contained considerable genetic diversity. Inoculations of tomato and pepper plants with strains from both hosts caused similar pith necrosis symptoms. Strains of both P. corrugata and P. viridiflava were grouped according to their geographical origin and not according to the original host. This is the first report of Pseudomonas viridiflava causing pith necrosis on pepper. [ABSTRACT FROM AUTHOR]

The time domain reflectometry (TDR) technique allows simultaneous estimation of apparent permittivity (εa) and bulk electrical conductivity (δa). In highly conductive media, however, the signal is completely attenuated, which precludes permittivity measurements. This study showed that δa can be estimated in conductive media by applying 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 coated with an insulator with a relative permittivity (εr) of 32.3. A good relationship (r² = 0.99) was found between the εa estimated, if possible, with P0 immersed in several conductive and nonconductive media and the corresponding values estimated with P50, P75, and P95 The results also show that, for δa values ranging between 0.4 and 0.75 S m-1, simultaneous measurements of εa and δa were only possible using the partially coated probes. A good correlation was found between the δa estimated with P0 inserted in different soil columns wetted with highly saline solutions (i.e., δa > 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 δa < 0.2 S m-1, the accuracy of the partially coated TDR probes for estimations of δa decreased as the percentage of the rod coating increased, with errors up to 292% when δa determined by P95 was compared with that estimated by P0. [ABSTRACT FROM AUTHOR]

Aims: To analyze the association between alcohol intake and the severity of injuries sustained from traffic accidents on a Mexican highway., Design: An observational unit evaluated drivers involved in auto accidents., Setting: Mexico-Cuernavaca Highway, Mexico. A 60 km-long road with many altitude variations and sharp curves., Participants: Three hundred and eighty-six drivers involved in traffic accidents between March and September, 1994., Measurements: A questionnaire was applied to the driver, an occupant or witness at the site of the accident to collect information about the driver, vehicle characteristics, type of accident, day-night occurrence, road section (Mexico-Cuernavaca or Cuernavaca-Mexico) and weather conditions. A physical examination was carried out to determine the presence and severity of injuries., Findings: There were 177 injured people, including 12 deaths, with rates of 67.5 injuries and 4.58 deaths per 10,000 km driven. Variables associated with alcohol intake (p < 0.05) included: severity of injuries, non-use of seat belt, vehicle size and occurrence at night. Risk factors for severe injuries were: alcohol intake (adjusted OR 6.1 CI 95% 1.6-24.0); non-use of seat belt (OR 4.9 CI 2.2-10.8), age < 25 years (OR 3.6 CI 1.0-12.7), age > 54 years (OR 6.0 CI 1.4-25.0), speed > 90 km/h (OR 2.6 CI 1.1-6.3) and occurrence at night (OR 2.6 CI 1.3-5.3)., Conclusions: Alcohol intake is a major risk factor for severe injuries from highway traffic accidents. Its association with other risk factors such as non-use of seat belt and excessive speed suggests the importance of designing interventions aimed at reducing alcohol intake among automobile drivers.