Evaluation of soil erodibility factor(k)for loess derived landforms of Kechik watershed in Golestan Province,North of Iran

The technique proposed by Wischmeier ＆ Smith for estimating the soil erodibility factor is among the most important methods in this regard. Given the high amounts of silt and lime content in loess soils of eastern parts of Golestan province in Iran, this study aims to evaluate the ability of Wischmeier ＆ Smith index to estimate the soil erodibility of this region. Soil erodibility was first obtained by Wischmeier nomograph and then was compared with the actual values obtained by selecting six plots and then performing physical and chemical tests on these samples. Using the nomograph, Wischmeier index was calculated to be about 0.05-0.092 Mg h MJ？1 mm？1. The results showed that Wischmeier index was 182, 4.11, 6 and 0.35 times than actual value in field with half-hour rainfall, Fournier index, SWAT value with half-hour rainfall and SWAT value with Fournier index, respectively. Obtained results showed that erodibility estimated by Wischmeier ＆ Smith index was higher than the actual measured value. Poor performance of this index in loess soils indicates the need for further research in this field.

Prediction of soil–water characteristic curve for Malan loess in Loess Plateau of China

To predict the soil-water characteristic curve(i.e.SWCC)of natural and remoulded Malan loess from soil physical properties,one-point methods for determining the SWCC that are much simpler than experimental methods are proposed.The predicted SWCC is presented in the form of the BRUTSAERT equation,in which the four model parameters can be estimated from soil physical properties using the best correlations obtained in the present study along with one measured data point.The proposed one-point methods are validated using the measured SWCC data reported in the literature.The results of validation studies suggest that the proposed one-point methods can provide reasonable prediction of the SWCC for natural and remoulded Malan loess.The measured data point should be within the transition zone;the measured suction is suggested between25to100kPa for natural loess,while between100to500kPa for remoulded loess.

Mechanical characteristics of intact Middle Pleistocene Epoch loess in northwestern China

In order to research the mechanical characteristics of intact Middle Pleistocene Epoch loess, triaxial shear tests and isotonic compression test of intact Middle Pleistocene Epoch loess were conducted by improved SJ-IA triaxial shear equipment. According to test results, it can be found that the intact Middle Pleistocene Epoch loess has the properties of shear dilatancy and shear shrinkage. With the increase of confining pressure, stress-strain curve develops from softening to hardening. The failure mode of intact Middle Pleistocene Epoch loess is shear failure with the rupture angle between 55° and 61°. And it is better to determine the yield stress （py, qy） of the intact loess under different confining pressures by using the εv-q/p curve. Along with the increase of confining pressure, yield deviatoric stress qy and yield spherical stress py present logarithmic relationship. Besides, the strength parameters, elastic modulus K and G of intact loess, are obtained, which are benefit for loess projects design.

Seismic Data Acquisition Techniques on Loess Hills in the Ordos Basin

High-resolution exploration for lithologic targets confronted with difficulties due to the original brought out from geophysical and geologic characteristics of the loess hills and the very thick deserts in Ordos. Scientific research since mid 1990s has conducted three acquisition techniques including the high-resolution crooked line survey in valleys, high-resolution multiple straight line survey and 3D survey, under different surface conditions and for different geological targets.

Relationships between Soil Depth and Terrain Attributes in a Semi Arid Hilly Region in Western Iran

Soil depth generally varies in mountainous regions in rather complex ways.Conventional soil survey methods for evaluating the soil depth in mountainous and hilly regions require a lot of time,effort and consequently relatively large budget to perform.This study was conducted to explore the relationships between soil depth and topographic attributes in a hilly region in western Iran.For this,one hundred sampling points were selected using randomly stratified methodology,and considering all geomorphic surfaces including summit,shoulder,backslope,footslope and toeslope;and soil depth was actually measured.Eleven primary and secondary topographic attributes were derived from the digital elevation model(DEM) at the study area.The result of multiple linear regression indicated that slope,wetness index,catchment area and sediment transport index,which were included in the model,could explain about 76 % of total variability in soil depth at the selected site.This proposed approach may be applicable to other hilly regions in the semi-arid areas at a larger scale.

Influence of environmental factors on land-surface water and heat exchange during dry and wet periods in the growing season of semiarid grassland on the Loess Plateau

On the basis of information from the project ＂Land-surface Processes and their Experimental Study on the Chinese Loess Plateau＂, we analyzed differences in land-surface water and heat processes during the main dry and wet periods of the semiarid grassland growing season in Yuzhong County, as well as the influences of these environmental factors. Studies have shown that there are significant differences in changes of land-surface temperature and humidity during dry and wet periods. Daily average normalized temperature has an overall vertical distribution of ＂forward tilting＂ and ＂backward tilting＂ during dry and wet periods, respectively. During the dry period, shallow soil above 20-cm depth is the active temperature layer. The heat transfer rate in soil is obviously different during dry and wet periods. During the dry period, the ratio of sensible heat flux to net radiation （H/Rn） and the value of latent heat flux to net radiation （LE/Rn） have a linear relationship with 5-cm soil temperature; during the wet period, these have a nonlinear relationship with 5-cm soil temperature, and soil temperature of 16℃ is the critical temperature for changes in the land-surface water and heat exchange trend on a daily scale. During the dry period, H/Rn and LE/Rn have a linear relationship with soil water content. During the wet period, these have a nonlinear relationship with 5-cm soil water content, and 0.21 m^3 m^-3 is the critical point for changes in the land-surface water and heat exchange trend at daily scale. During the dry period, for vapor pressure deficit less than 0.7 kPa, H/Rn rises with increased vapor pressure deficit, whereas LEIRn decreases with that increase. When that deficit is greater than 0.7 kPa, both H/Rn and LE/Rn tend to be constant. During the wet period, H/Rn increases with the vapor pressure deficit, whereas LE/Rn decreases. The above characteristics directly reflect the effect of differences in land-surface environmental factors during land-surface water and heat exchange processes, and indirectly reflect the influences of cloud precipitation processes on those processes.

Apatite Loss in Pothwar Loess Plain(Pakistan) Fits a Simple Linear Reservoir Model

Apatite is the dominant phosphorus(P) mineral in early stages of soil development, and its redistribution as labile forms under pedogenesis controls terrestrial bioavailability. Quantitative distribution of labile forms of P and apatite-P was examined in Pothwar Loess Plain, Pakistan where the degree of pedogenesis varied with relief. Four soil types, Typic Ustorthents(Rajar), Typic Calciustepts(Missa), Udic Calciustepts(Basal), and Udic Haplustalfs(Guliana), were sampled from three replicated locations at genetic horizon level. With the exception of total P value at surface, the mean total and apatite-P decreased towards the surface in Udic Haplustalfs and Udic Calciustepts where dicalcium and octacalcium phosphate increased toward surface. Iron(oxides and oxyhydroxides) adsorbed and occluded P forms were also in greater quantities in Udic Haplustalfs and increased toward the surface, whereas they were lowest and uniform in the Typic Ustorthents. Aluminum- and organic P correlated with soil organic matter. Apatite-P decreased exponentially with an increase in the sum of iron adsorbed and occluded P fractions, and fitted the equation M(x)= M0 [1- exp(-wx)] with r2= 0.996, where M(x)is the mean apatite-P concentration in solum, M0 is the apatite-P content in the loess sediments, x is the cumulative iron adsorbed and occluded P, and w is an empirical factor indicating the change rate of apatite-P in the loess. From the calculated apatite-P of 740 mg kg-1at the time of deposition, mean apatite-P loss was 60% in Udic Haplustalfs, 33% in Udic Calciustepts, 23% in Typic Calciustepts, and 8% in Typic Ustorthents. The transformation of soil P to labile forms was faster and deeper in level or slight depressions followed by gently sloping areas in wide plains, and was the least in the gullied land.