Mansoreh Bameri; Farhad khormali; Hossein kheirabadi
Abstract
Introduction. Soil is an essential part of the environment. It is important for the production of food and other crops. Soil erosion and sedimentation are complicated and least well-known environmental problems worldwide (Mahmoodabadi et al, 2014). Recently, the application of compounds that modify and ...
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Introduction. Soil is an essential part of the environment. It is important for the production of food and other crops. Soil erosion and sedimentation are complicated and least well-known environmental problems worldwide (Mahmoodabadi et al, 2014). Recently, the application of compounds that modify and improve soil quality and also reduce soil erodibility has been more thoroughly researched. These compounds are known by the common name of soil amendments with a relatively high variety such as gypsum, basanite, zeolite, chemical amendments, organic additives, a variety of chemical, biological and composite polymers, soiltac, fungi, polyvinyl acetate, vermicompost and cattle manure, biochar, straw mulching and cyanobacteria and bacteria (Behzadfar et al, 2017). The objective of this study was to investigate the influence of bentonite clay and slope gradient on runoff and sediment concentration and some hydraulic Characteristics in the Loess soil using a rainfall simulator. Materials and Methods The experiments were conducted using a rainfall simulator at the Soil Erosion and Conservation Laboratory, Gorgan University of Agricultural Sciences and Natural Resources, Iran. The soil used for the experiments is taken from the surface layer (0-30 cm depth) of loess lands from Golestan province (37° 55ʹ N and 55° 29ʹ E). The soil sample at first was air-dried, thoroughly mixed and then crushed to pass through 10 mm sieve size. Experiments were done as factorial based on completely random design with three replications. The factors were the bentonite clay at four level (0, 2, 5 and 10 % weight) and slope steepness at three level (10, 20 and 30%). In all experiments, each soil sample was put in the flume, then was saturated from the bottom for 24 h. Afterwards, the drainage water was removed out of the tray, and the experiment lasted for 45 min. For each rainfall event, the sediment-laden overland flow was sampled at selected time intervals and volumetrically measured. The sediment-laden overland flow was sampled at several time intervals and the sediment concentration was determined . The sediment in the collected samples was allowed to settle, separated from the water, and dried in an oven at 105 °C for 24 h. The sediment concentration was determined as the ratio of dry sediment mass to sampled runoff volume for each time interval.Different hydraulic parameters including flow depth, shear stress, stream power, and unit stream power were measured.Results and Discussion The result showed that the sediment concentration decreased with increasing levels bentonite at all slopes. At 10 % slope steepness, the mean sediment concentration varied 32.48 in the control treatment to 24.67 kg m-3 at level 3 bentonite treatment. At 30% slope the corresponding value were 474.52 and 224.14 kg m-3. Therefore, with increasing slope steepness the sediment concentration increased. Totally, the use of bentonite at level 10 % weight could decrease 46% of sediment concentration in comparison with control treatment. Defersha and Melesse (2012) found that rain intensity and slope gradient had significant influences on sediment concentration. Slope gradient is important as more soil particles are splashed down-slope than up-slope (Dunne et al. 2010; Grismer 2012). According to Fig. 2, the obtained flow depth was 1.92×10−4, 1.92×10−4, 1.92×10−4 and 1.92×10−4 m for 0, 2, 5, 10% clay treatment, respectively. Also, the depth flow ranged from 3.6×10− 4 to 1.96×10−4 m on 10 to 30 % slopes. Totally, the depth of flow decreased with increasing slope steepness for all treatments. In fact, due to higher flow velocities at steeper slopes, shallower flow depths were achieved. Statistical analysis (Table 2) confirmed a significant positive main effects of application levels of bentonite and slope on shear stress, power flow and unit power flow. The clay treatment showed significant reductions ranging from 2 to 50% compared to the control treatment for all slopes. Unit stream power varied from 0.0084 to 0.0095 ms-1, 0.0176 to 0.0241 ms-1 and 0.030 to 0.057 ms-1 for 10, 20 and 30 % slope, respectively. Totally, with increasing slope steepness, all the hydraulic parameters, except flow depth, increased. While with increasing percentage of bentonite clay, shear stress and depth flow and stream power, decreased. Consequently, the maximum values were observed at the steepest slope (30 %) and control treatment (0%). Conclusion Based on the results obtained during the present study, it can be concluded that the bentonite can be considered as an effective modifier of soil physicochemical properties leading to better performance in soil and water conservation in loess lands. Keywords: Bentonite, Simulator Rain, Slope, Sediment Concentration, Hydraulic Characteristics
Soil Physics, Erosion and Conservation
shamsollah ayoubi; zanyar feizi; Mohammad reza Mosaddeghi; Ali asghaar besaltpour
Abstract
Investigating the application of biochar, bentonite clay and polyvinyl acetate polymer on some mechanical properties of sand deposits IntroductionWind erosion seriously threatens bare soils and is recognized as a global environmental problem; however, little is known about this process in comparison ...
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Investigating the application of biochar, bentonite clay and polyvinyl acetate polymer on some mechanical properties of sand deposits IntroductionWind erosion seriously threatens bare soils and is recognized as a global environmental problem; however, little is known about this process in comparison to rainfall or tillage erosion. Due to the heavy costs of controlling wind erosion and the difficulty of detecting which control measure is the most effective, the correct selection of technical methods is indispensable for a suitable land management. Since the last decades, the methods of sand stabilization studied are diverse, but basically based on wind speed reduction by including chemical, mechanical and biological methods. One of the most important methods of stabilizing sandy soils is the use of mulches. In recent years, due to the disproportionate development of residential in peri-urban areas, humans use polymeric and oil mulches to stabilize sandy soils. Therefore, in this research, the effects of bentonite clay, polyvinyl acetate and palm biochar on reducing soil erosion by wind in peri-urban areas were investigated.Methods and Materials Three selected treatments were compared with a control plot without any treatment: palm biochar, polyvinyl acetate and bentonite clay. In order to prepare the palm biochar, palm remnants including the trunk, foliage and palm leaves were poured into the mill and turned into small pieces. The fragments were passed through a 2 mm sieve. The remnants transmitted from the sieve were poured into the trays of the discharger unit and placed inside a discharger at 350°C for 4 hours, and the biochemicals were prepared to the extent necessary for this research. Polyvinyl acetate treatment was provided by Isfahan Resin Co. and the bentonite clay by the Derin Kashan enterprise (both of them from Isfahan, Iran). To apply the treatments, each of them was mixed with a certain proportion of water per m2: i) 20 g l-1of palm biochar treatments; ii) 7 g l-1 of polyvinyl acetate treatment; and, iii) 20 g l-1 of bentonite clay.In order to apply the treatments, 36 galvanized trays with a same size (5×35×105 cm) were prepared and filled up from the air to the top edge with sand. After 1, 2, 4, 10 and 20 weeks some mechanical and physical properties were measured in laboratory. Results and Discussion A significant difference was observed among different treatments in terms of the impact on aggregates formations and stabilities at different moments. The application of bentonite clay treatment significantly increased the stability of formed aggregates compared to control treatment. The rest of treatments showed lower aggregability. The mean weigh diameter (MDW) for the control plot was 0.28 mm. The lowest MWD was obtained by the palm biochar treatment, which increased by 20.1, 14.9, 9, 2.5 and 1.6% after the first, second, fourth, tenth and twentieth weeks of application, respectively. Polyvinyl acetate treatment increased MDW by 65.1, 61.6, 58.8, 41.9 and 31.5% after the first, second, fourth, tenth and twentieth weeks, respectively. The highest MWD was obtained by bentonite clay treatment, which generated an increase by 77.8, 71, 65.1, 59.9 and 49.7% in the first, second, fourth, tenth and twentieth weeks, respectively). The images from thin sections of bentonite clay and polyvinyl acetate treatments showed that soil particles were joined to form larger aggregates in all of cases.No significant differences was observed for hydraulic conductivity at different times were observed. There was a significant difference among different treatments at different monitoring periods. The application of bentonite clay significantly reduced the fractal dimension. On the contrary, the lowest effect was registered for the palm biochar treatment. The effect of bentonite clay treatment on soils was higher than other selected treatments showing a reduction by 10.6, 9.7, 8.7 6.7 and 6.3% in the first, second, fourth, tenth and twentieth weeks, respectively. The impact of different treatments on shear resistance showed that the application of the selected treatments significantly increased the shear strength in all the cases. Among the selected treatments, the effect of bentonite clay treatment on shear resistance was higher than other treatments. The lowest and the highest shear resistance were registered for the palm biochar and bentointe clay, respectively. Palm biochar increased shear resistance by 9.3, 9.3, 8, 5.3 and 3.3% compared to the control plot in the first, second, fourth, tenth and twentieth weeks after its application. On the other, bentonite clay registered the highest improvement in shear resistance by 44.7, 44.7, 42.7, 37.3 and 31.3% in the first, second, fourth, tenth and twentieth weeks, respectively. Keywords: Mulches, Bentonite, Clay, Biochar, Palm, Mechanical properties
