The generalized second law of gravitational thermodynamics on the apparent horizon in f(R)-gravity

We investigate the generalized second law (GSL) of thermodynamics in the framework of $f(R)$-gravity. We consider a FRW universe filled only with ordinary matter enclosed by the dynamical apparent horizon with the Hawking temperature. For a viable modified gravity model as $f(R)=R-\alpha/R+\beta R^{2}$, we examine the validity of the GSL during the early inflation and late acceleration eras. Our results show that for the selected $f(R)$-gravity model minimally coupled with matter, the GSL in the early inflation epoch is satisfied only for the special range of the equation of state parameter of the matter. But in the late acceleration regime, the GSL is always respected.Comment: 10 pages, accepted by Europhys. Lett. 201

Effect of Pretreatment with Indole-3-Butyric Acid on Germination Characteristics of Pinto Bean Seed under Salt Stress

In order to study the effect of seed priming by indole-3-butyric acid (IBA) on germination characteristics of pinto bean under salinity stress, a factorial laboratory experiment, based on completely randomized design with three replications, was carried out at the Faculty of Agricultural Sciences, University of Guilan, Rasht, Iran, in 2011-2012. Three levels of pretreatment (0, 10 and 20 mg/L IBA) and five levels of salinity stress due to NaCl (0, 1, 2, 3 and 4 dS/m) were considered. Results represented the significant effect of IBA on shoot length, root dry matter as well as allometric coefficient. Salinity had significant effect on shoot and root length, shoot dry weight, vigor index and allometric coefficient. While, interaction effect of IBA and salinity was significant only for allometric coefficient. In this experiment, the rate and percentage of germination were not affected by any of the treatments. Comparison of means showed that increasing IBA concentration resulted in an increase in shoot length (1.9 to 2.1 cm), shoot dry weight (0.03 to 0.05 gm) and allometric coefficient (0.71 to 1.06 cm), while increased salinity resulted in a decrease in root length (2.6 to 2 cm), vigor index (202.8 to 147.7) as well as allometric coefficient (1.1 to 0.78 cm). Increasing salinity increased shoot length first, and then reduced it. Overall, it appears that application of IBA for pretreatment of pinto been seeds could enhance seedling establishment under saline conditions through the improvement of root length

Letter to the Editor

Depression and Posttraumatic Stress Disorder among Road Traffic Accident Victims Managed in a Tertiary Hospital in Southern Nigeria: The Methodological Issu

Spatial analysis of soil surface hydraulic properties : is infiltration method dependent ?

The management of irrigated agricultural fields requires reliable information about soil hydraulic properties and their spatio-temporal variability. The spatial variability of saturated hydraulic conductivity, K-s and the alpha-parameter alpha(VG-2007) of the van Genuchten equation was reviewed on an agricultural loamy soil after a 17-year period of repeated conventional agricultural practices for tillage and planting. The Beerkan infiltration method and its algorithm BEST were used to characterize the soil through the van Genuchten and Brooks and Corey equations. Forty field measurements were made at each node of a 6 m x 7.5 m grid. The soil hydraulic properties and their spatial structure were compared to those recorded in 1990 on the same field soil, through the exponential form of the soil hydraulic conductivity given by the Gardner equation, using the Guelph Pressure Infiltrometer technique. No significant differences in the results obtained in 1990 and 2007 were observed for either particle-size distribution or dry bulk density. The mean value of alpha(vG-2007) was found to be identical to that of alpha(G-1990), while that of Ks-2007 was significantly smaller than that of Ks-1990. In contrast to the Gardner equation, the van Genuchten/Brooks and Corey expression was found to be more representative of a well-graded particle-size distribution of a loamy soil. The geostatistical analysis showed the two parameters, K-s and alpha(vG-2007), were autocorrelated up to about 30 and 21 m, respectively, as well as spatially positively correlated within a range of 30 m. Despite the difference in the mean values of K-s between the two studies, the spatial structures were similar to those found in the 1990 experiment except for the covariance sign. The similarity in autocorrelation ranges indicate that the spatial analysis of soil hydraulic properties is independent of the infiltration methods (i.e., measurement of an infiltration flux) used in the two studies, while the difference in the covariance sign may be linked to the use of two different techniques of soil hydraulic parameterization. The covariance values found in the 2007 campaign indicates a positive relationship between the two parameters, K-s and alpha(vG-2007). The spatial correlations of soil hydraulic parameters appear to be temporally stabilized, at least within the agro-pedo-climatic context of the study. This may be attributed to the soil textural properties which remain constant in time and to the structural properties which are constantly renewed by the cyclic agricultural practices. However, further experiments are needed to strengthen this result

Temporal variability in soil hydraulic properties under drip irrigation

Predicting soil hydraulic properties and understanding their temporal variability during the irrigated cropping season are required to mitigate agro-environmental risks. This paper reports field measurements of soil hydraulic properties under two drip irrigation treatments, full (FT) and limited (LT). The objective was to identify the temporal variability of the hydraulic properties of field soil under high-frequency water application during a maize cropping season. Soil hydraulics were characterized using the Beerkan infiltration method. Seven sets of infiltration measurements were taken for each irrigation treatment during the cropping season between June and September 2007. The first set was measured two weeks before the first irrigation event. The results demonstrated that both soil porosity and hydraulic properties changed over time. These temporal changes occurred in two distinct stages. The first stage lasted from the first irrigation event until the root system was well established. During this stage, soil porosity was significantly affected by the first irrigation event, resulting in a decrease in both the saturated hydraulic conductivity K-s and the mean pore effective radius xi(m) and in an increase in capillary length alpha(h). These hydraulic parameters reached their extreme values at the end of this stage. This behavior was explained by the "hydraulic" compaction of the surface soil following irrigation. During the second stage, there was a gradual increase in both K-s and xi(m) and a gradual decrease in alpha(h) when the effect of irrigation was overtaken by other phenomena. The latter was put down to the effects of wetting and drying cycles. soil biological activity and the effects of the root system, which could be asymmetric as a result of irrigation with only one drip line installed for every two plant rows. The processes that affected soil hydraulic properties in the two irrigation treatments were similar. No significant change in xi(m) and alpha(h) was observed between FT and LT. However, as a result of daily wetting and drying cycles, which were strongest in LT, the soil in this treatment was found to be more conductive than that of FT. This showed that most of the changes in pore-size distribution occurred in the larger fraction of pores. The impact of these temporal changes on the dimensions of the wetting bulb was studied using a simplified modeling approach. Our results showed that there were marked differences in the computed width and depth of wetting bulb when model input parameters measured before and after irrigation were used. A temporal increase in capillary length led to a more horizontally elongated wetting bulb. This could improve both watering and fertilization of the root zone and reduce losses due to deep percolation. As a practical result of this study, in order to mitigate agro-environmental risks we recommend applying fertilizers after the restructuration of tilled soil. Further studies using improved models accounting for temporal changes in soil hydraulic properties are needed

Les impacts du semis direct et le système conventionnel sur certaines caractéristiques hydrauliques de la couche arable dans le climat méditerranéen

Soil tillage is the guiding component of soil management and consequently has far-reaching implication for agroecosystems. Understanding structures and functions of soil under conventional tillage and no-tillage is an essential requirement for any future farming concepts. Tillage greatly affects soil structure in topsoil and, to a certain degree, in the subsoil. It can change soil behaviour at the topsoil with regard to infiltration, runoff, etc. Several methods have been developed to study hydraulic characteristics of topsoil. In this study Beerkan method, which is a simple in situ method using a single ring infiltration, was used to better understand tillage and no-tillage impacts on transmission properties of topsoil. This method depends on an algorithm namely BEST. This study was carried out at Lavalette experimental station in Montpellier in the South of France. Two different tillage measurement series were done. The first series was performed after harvest of durum wheat and the second one was performed after sowing. By using those two series as input data, BEST model can estimate saturated hydraulic conductivity, sorptivity, the mean characteristics of hydraulically functional pore size and capillary length. The results indicate that after harvest hydraulic properties of topsoil were not significantly different. However after sowing, saturated hydraulic conductivity was significantly higher (