جستجوی مقالات مرتبط با کلیدواژه « منحنی مشخصه رطوبتی خاک » در نشریات گروه « آب و خاک »

Although several mathematical models have been proposed to describe the soil moisture characteristic curves, not one model is suitable for all soil types. The purpose of this study was to determine the best model and Pedotransfer function to describe this curve in Mahidasht plain, Kermanshah province. Soil samples were collected from four locations at three depths. The soil moisture characteristic curve of the samples was determined using sandbox and pressure plates. The coefficients of van Genuchten and Brooks-Cory were determined based on measured data using RETC software. The estimated curve by RETC software was compared with the curve drawn based on measured data. The results showed that all models have almost the same estimations and only the Brooks-Corey model overestimates the moisture at low suctions. Based on the results, it can be stated that among the four studied models, the van Genuchten-Bordin model with m = 1-2/n (RMSE = 0.01 and ME = 0.002) is the most suitable model in the study area. The results also showed that the studied Pedotransfer functions have acceptable accuracy for estimating the soil moisture characteristic curve and the modified Sepaskhah-Bondar model (RMSE = 0.1 and ME = 0.02) is the best Pedotransfer function for soils of the Mahidasht. Then the parameters of the most suitable PEDOTRANSFER function for the soils of the study area were calibrated. Although the results of this study can be useful for use in other soils, the coefficients of these functions should be calibrated in each region.

Today, one of the most important challenges of the present and the future, especially in the arid regions of the world, is the issue of water shortage and in some cases the water crisis. One of the ways to improve water productivity and better water management in agricultural sector as the largest consumer of water is the use of super-absorbent materials to improve soil texture, increase soil water retention, reduce erosion and increase germination. The aim of this study is to evaluate the effect of Aquasource superabsorbent polymer on physical parameters and soil-water characteristic curves (SWCC) of different soil textures.  

Aquasource is a new generation of potassium-based superabsorbent polymers that are biodegradable and free of destructive acrylamide compounds. In order to evaluate the effect of Aquasource hydrogel on hydro-physical properties of soils, some experiments in the form of a completely randomized design with 3 replications was performed. The first factor was different levels of superabsorbent (0, 0.5, 1 and 2% by weight of superabsorbent/soil) and the second factor was three different soil textures (sandy-loam, clay-loam and silty-clay). SWCCs related to all treatments were determined by determining the moisture content of the samples at different pressures (0, 0.3, 0.5, 1, 3, 6, 9 and 15 bars) using a pressure plate device. Then, to obtain the soil moisture characteristic curve parameters  in each sample, two softwares RETC (v.6.02) and Rosetta (v. 1.1) were used.  

The results of variance analysis and mean comparisons based on Duncan's test showed that in all soil textures studied, the application of superabsorbent and the increase Aquasource amounts, increased the moisture contents at the field capacity and permanent wilting point. However, the highest amount of soil available water for plant use in sandy loam, clay loam and silty clay textures was 9.8%, 13.8% and 12.7%, respectively, and they are related to the use of 0.5% w/w of superabsorbent in these treatments (Fig. 1). The use of larger amounts, up to 2%w/w, reduced the soil available water for plant use. This issue can be related to the reducing the interaction of soil particles and polymers with increasing the amount of superabsorbent application in soil. At high levels of superabsorbent consumption, the contact of the hydrogel with the soil particles is reduced, followed by the aggregation of the superabsorbent. This prevents the proper exchange  between the superabsorbent and the surrounding soil, and thus despite the presence of moisture in the soil-superabsorbent system, this moisture cannot be used for the plant, so that in all three soil textures the lowest amount of plant available water belongs to the treatments of 2% w/w of Aquasource. The results of statistical analysis for estimating the parameters of the soil-water characteristic curve due to the application of different levels of superabsorbent in different soil textures using two software RETC (v.6.02) and Rosetta (v. 1.1) showed that the fit The Van-Genuchten (Moallem) model in RETC software in all treatments has provided a good approximation of the parameters of the soil-water characteristic curve (R2> 0.98). Also, with increasing the amounts of superabsorbent, the accuracy of the model in estimating the parameters decreased to some extent.    

Application of Aquasource superabsorbent and increasing the application level of this superabsorbent polymer (from 0 to 2% by weight of superabsorbent/soil) in sandy-loam, clay-loam and silty-clay soil textures caused an increase in the moisture content at field capacity and permanent wilting point. Application of 2% W/W in sandy-loam, clay-loam and silty-clay soil textures increased the moisture content at the field capacity by about 2.4, 1.6 and 1.5 times, respectively, compared to the control treatments of each soil textures. However, the highest amounts of plant available water in all three soil textures were obtained by applying 0.5% W/W (superabsorbent/soil). Application of 0.5% W/W in sandy loam, clay loam and silty clay textures increased the plant available water by about 1.23, 1.19 and 1.12 times compared to the control treatments in each soil textures, respectively. However, the use of larger amounts reduced the plant available water. At low levels of Aquasource application, the interaction between the   superabsorbent polymer and the soil particles in the soil/polymer system facilitates the transfer of moisture stored in the superabsorbent to soil particles. However, increasing the application level of this polymer up to 2% W/W has an inhibitory effect and in this case, the interaction between the polymer and soil particles is reduced, which leads to a lack of proper drainage of moisture from the polymer.   Acknowledgement The authors would like to thank Agricultural Engineering Research Institute for supporting this research.

Soil moisture characteristic curve (SMCC) is an important hydraulic properties in modelling of water movement and solute transport in unsaturated zone of soil, which its direct measurement in a laboratory is expensive, time-consuming and laborious. Therefore, the objective of this study was to compare the fitting capabilities of several SMCC fractal (Tyler and Weatcraft, 1990; Rieu and Sposito, 1991; Perfect, 1999 and Bird et al., 2000) and empirical models (Brooks and Corey, 1964; Campbell, 1974 and van Genuchten, 1980) to the observed data and to select the appropriate models. For this purpose, fifty-four soil samples were randomly collected from Ghorveh-Dehgolan plain and some important physical and chemical properties of soils were measured in the soil laboratory. The SMCC fractal and empirical models were fitted to the measured data based on the least esquare error approach using the solver toolbox of EXCEL software. In order to evaluate fitting quality of the proposed models, three statistical parameters including coefficient of determination (R2), root mean square error (RMSE) and Akaike information criterion (AIC) were used. The results indicated that all models did well with R2 ranging from 0.75 to 0.99. Bird et al., (2000) and van Genuchten (1980) models are selected as the best models, respectively, based on the highest R2 and the lowest RMSE and AIC. Rieu and Sposito (1991) model was the weakest, although the average R2 was greater than 0.75 and the average RMSE was smaller than 0.071 cm3/cm3.

In this study, one-dimensional equation of  water flow in saturated-unsaturated soil was solved using finite volume method and implicit scheme. The relationship between unsaturated moisture content and pressure load was determined using Van Genechten and Brooks-Corey hydraulic functions. The validation results of the model showed that the model accurately estimated the load pressure values. The Root Mean Square Error of the pressure load for the Van Genuchten and Brooks-Corey hydraulic functions was 0. 0181 and 0. 0439 meter, respectively. After confirmation of the results of the model, the effects of three different methods for estimating the hydraulic parameters of soil by ROSETTA software were evaluated on the soil moisture characteristics curve. In the first method the complete ROSETTA model, in the secound mehtod  only soil texture and in the third method in addition of soil texture, poros medial shape parameter (l=0. 5) were considered. Comparison of the results of the model with the Hydrus 1D model showed that the prepared model had very good accuracy in all cases. Also, the results showed that with time passage and more soil drying, due to the effect of physical properties and soil porosity, the difference between three methods increases.

The range of soil water content where plant growth is least limited by water potential, soil aeration or mechanical resistance is called least limiting water range (LLWR). This study evaluated the values of LLWR determined according to the procedures proposed by da Silva et al. with those calculated on the basis of sunflower plant (Helianthus annuus L) response (LLWRP). In both methods LLWR is taken as the difference between the two soil moisture limits designated as upper (θUL) and lower (θLL). In the first method, the two limits are determined basically from the soil moisture and soil resistance characteristic curves, almost overlooking the plant type and its particular needs or behaviors. In the second method, as proposed in this research, the two limits are determined based on the stomatal response in a sandy clay loam soil packed into PVC tubes (called pots hereafter) with 30 cm diameter and 70 cm height at three compaction levels (soil bulk density equal to 1.75, 1.55 and 1.35 Mg.m-3) designated as D1, D2 and D3. Each pot was planted with three pre-soaked sunflower seeds and pots were kept under optimum condition until onset of the flowering stage. At this time two successive drying cycles were imposed and soil moisture and midday stomatal conductance were routinely measured. LLWRP were computed on the basis of relationship between soil matric suction and stomatal conductance. Results showed that on the basis of stomatal conductance behavior water uptake began at the soil matric suctions of 44, 16, 60 and continued up to 17394,31614, 39983 cm in D1, D2 and D3 treatments, respectively. Appreciable differences were observed between LLWR and LLWRP particularly when the lower limit moisture suction (equivalent to θUL for LLWR) was set at 330 cm (LLWR330). LLWR330 values of 0.148, 0.147 and 0.080 cm3cm-3 were obtained for D1, D2, D3 treatments, respectively, which were 51, 49 and 63 percent lower than the corresponding LLWRP values. This differences imply that the two moisture limits (θUL and θLL) proposed by da Silva et al. may not be applied indiscriminately for all plants and thus need to be modified according to plant needs or responses.

Suitable land management result in improving the soil hydro-physical properties and erosion control in arid and semi-arid regions. Application the cover crop as bioengineering tool is a good choice to improve soil hydro-physical properties and to protect the soil against erosive factors. Anionic polyacrylamide (PAM) has been widely used in this field, as well. In literature, the individual effect of Vetiver and PAM on Soil structural stability and erosion indices has been investigated. The objective of this study was to investigate and compare the effect of vetiver cultivation system, PAM and their combination on hydraulic properties and physical quality index of soil in experimental plots.
This study was performed in loamy soil plots of a loamy soil in Agriculture Campus, Ferdowsi University of Mashhad. The experimental treatments include vetiver cultivation (VP0), PAM (20 (P2) and 40 (P4) kg ha-1), simultaneous application of vetiver and PAM concentrations (VP2, and VP4). In addition, P0 (no PAM and vetiver) was regarded as control treatment. The soil moisture contents for different treatments were measured at 0, 5, 10, 50, 100, 300, 500, 1000, and 1500 kPa. According to this data the van Genuchten’s equation was fitted to the soil moisture characteristic curve using the RETC software, and the parameters of model were estimated by the least square error methods. Also, saturated hydraulic conductivity and soil physical quality index were determined. This study was designed based on randomized complete blocks in a factorial arrangement with 3 replications. Data of van Genuchten’s parameters, Sgi index, and Ks were analyzed using SPSS 23 software.
The results showed that vetiver and PAM through increasing the aggregation and stability of soil structure, and improving the structural properties increased θs, and ks. However, the effect of PAM on ks depends on its concentration and viscosity. Vetiver decreased θr, and the hydrophilic molecules of PAM polymer increased θr. Vetiver increased considerably the value of α parameter and decreased air entry value by increasing the soil macro-pores. Although, the value of α parameter was not affected by PAM. Vetiver increased the value of n parameter, while PAM decreased its value. Also, vetiver and PAM increased the Sgi through the aggregation and improving the soil structure and physical condition. In general, vetiver had more effect on parameters of van Genuchten model and improvement of soil hydraulic properties than the PAM and the combination of vetiver and PAM showed the greatest effect.
Generally, the results of this research indicated that the very low cost and long-term bioengineering technique based on vetiver system can be recommended to improve physical and structural properties of soil in semi-arid regions such as Iran.

The need for water storage is steadily growing because of increasing water demands due to growing population in arid and semiarid areas such as Iran where droughts occur in succession. The use of superabsorbent polymer materials in agriculture is one of the considered approaches to improve the soil structure in semi- heavy and heavy soils. In this study, the use of superabsorbent A300 and its effects on saturated hydraulic conductivity, available water content, porosity and moisture characteristic curve was evaluated in silty loam soil. A completely randomized design with four levels (zero, 1, 2, 3 g/kg soil) and three treatments was used for statistical analysisin research field of Shahid Chamran university. The results show that increase 1.68 saturated hydraulic conductivity soil in 0.3 weight precent to the control. The increase of porosity for treatments0.1, 0.2 and 0.3 weight percent of controls versus 8.03, 9.76 and 22.11 respectively. Statistical indicators applied in RETC software shows the Van Genuchten model (m=1-1/n) has the best simulation accuracy by comparing the observed and predicted soil moisture values.

Hydraulic conductivity is an important parameter in the design of geotechnical structures such as earth dam، floor construction، retaining walls and environmental structures. In unsaturated soils، hydraulic conductivity is a function of moisture content and soil water suction i. e. soil moisture characteristic curve. In this study، the values of unsaturated hydraulic conductivity in two soil types (Ramjerdi and Molasadra core dam series) at 5 different compactions using Gardner method were measured. Then، the unsaturated hydraulic conductivity was estimated by different models using the soil moisture characteristic curve and was compared with measured values. The results showed that Fredlund and Xing models predict the soil moisture characteristic curves more accurately compared with van Genuchten model. For Ramjerdi soil series and up to nearly 0. 25 volumetric water content، (VGM) and (FM) models indicated a good estimation for unsaturated soil conductivity. Also، for Molasadra core dam none of the models resulted in acceptable estimations for unsaturated hydraulic conductivity.