Soil science
A.R. Vaezi; R. Bigdeli
Abstract
Introduction
Rill erosion is one of the main factors of soil degradation, especially in rainfed lands in semi-arid regions. These soils have relatively lower organic matter content with weakly-aggregated units, which increases their susceptibility to water erosion processes. Conventional tillage ...
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Introduction
Rill erosion is one of the main factors of soil degradation, especially in rainfed lands in semi-arid regions. These soils have relatively lower organic matter content with weakly-aggregated units, which increases their susceptibility to water erosion processes. Conventional tillage systems are adversely affect on soil structure and surface soil cover in rainfed lands. Raindrop energy and flow shear stress are the main erosive factors in the slope lands. The raindrop impact destroys soil structure and changes it to erodible unites; micro-aggregates and single particles, and so makes them to more detachment. A few studies have been done on the role of raindrop impact to soil erosion by water. Nevertheless, there is no sufficient information on the effect of raindrop impact on soil loss in the rills particularly in semi-arid regions. Therefore, this study was conducted to investigate the role of raindrop impact on soil loss from rills in various soil textures under different rainfall intensities.
Materials and Methods
A laboratory experiment was performed on two soil textures (clay loam and sandy loam) under four rainfall intensities (30, 50, 72 and 83 mm.h-1) in two rainfall conditions (under raindrops impact and without raindrops impact). Soil samples (0-30 cm) were taken from a semi-arid region in Zanjan province in 2020. The experiments were set up in an erosion flume with 100 cm long and 60 cm width and 15 cm depth which were exposed to simulated rainfalls for 30 min duration. Runoff and soil loss were measured at three rills under slope gradient 10% in the two rainfall conditions for each rainfall intensity. Soil loss from rills was determined as the mass of sediment collected from rill outlet per rill surface area (g.m-2). Under raindrop impact, the soil was exposed directly to raindrop impact and under without raindrop impact, a metal mesh sheet was used to eliminate raindrops impact to soil surface. The role of raindrops impact to runoff and soil loss was computed from the difference of runoff and soil loss under raindrops impact and without raindrops impacts. A t-test was used to assess the role of raindrops impact between the two rainfall conditions for the soils and rainfall intensities.
Results and Discussion
Results indicated that runoff production and soil loss were significantly affected by the soil texture and rainfall intensity. Runoff and soil loss under raindrops impact increased in the soils with increasing rainfall intensity. Clay loam showed more runoff production and soil loss than sandy loam which was associated to lower aggregate stability and hydraulic conductivity. Runoff and soil loss in the two soils and four rainfall intensities were significantly affected by raindrops impact. Runoff production and soil loss except to 72 mm.h-1 rainfall intensity were very higher under raindrop impact than without raindrop impact. It seems under 72 mm.h-1 rainfall intensity, raindrops impact varied the rill’s morphology and prevent more runoff production. Runoff production in clay loam and sandy loam under raindrop impact were increased by 44 and 36 percent, respectively (p< 0.01). Soil loss resulted by raindrop impact in clay loam and sandy loam increased by 53 and 62 percent, respectively (p< 0.01). Raindrops impact had more importance in soil loss rather than runoff production. This result is related to the role of raindrops impact in destroying aggregates and producing more erodible soil particles and closing soil macrospores and declining water infiltration. The role of raindrop impact in runoff production and soil loss varied among the rainfall intensities. A slight reduction in the role of raindrop impact in runoff and soil loss was occurred with increasing rainfall intensity, especially in sandy loam.
Conclusion
The role of raindrop impact in runoff production and soil loss was significantly affected by soil type and rainfall intensity. Raindrops impact has more important in runoff and soil loss in the soils having higher aggregate stability and more hydraulic conductivity. The role of raindrop impact in runoff and soil loss in these soils declines with increasing rainfall intensity. In general, maintain soil surface cover is essential to control raindrops impact and decrease runoff and soil loss in semi-arid areas. The importance of soil surface cover is most obvious under different rainfalls in weakly-aggregated soils which are dominant in many slope lands. Also, soil surface cover has important role in controlling runoff and soil loss under heavy rainfalls in soils with more water-stable aggregates. Prevention from intensive tillage and using conservation tillage systems such as minimum tillage are effective strategies in controlling raindrop impact in rainfed lands in semi-arid regions.
A.R. Vaezi; E. Mohammadi; N. Sadeghian
Abstract
Introduction: Rills are usually found on the sloping fields worldwide, especially in semi-arid slopes, where vegetation covers are often poor and soils are weakly aggregated. Rill erosion is recognized as an important process of water erosion on agricultural land in these regions and causes a grate amount ...
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Introduction: Rills are usually found on the sloping fields worldwide, especially in semi-arid slopes, where vegetation covers are often poor and soils are weakly aggregated. Rill erosion is recognized as an important process of water erosion on agricultural land in these regions and causes a grate amount of soil loss. Understanding rill erosion rate is important in the prediction of soil erosion and the prevention of soil loss in the lands. Rill erosion is often easy to observe but difficult to measure because of its complexity and stochastic nature. A common method used to determine rill erosion rate is measuring sediment concentration distribution of eroding rill flow under different flow rates. However, it is not only time-consuming but also had to measure. The volume Replacement Method is an easy method to estimate soil loss from rills in the sloped lands. Limited information is available concerning the ability of this method in different soil textures under slope gradients. Therefore, this study was conducted to evaluate the ability of the method to estimate rill erosion of semi-arid soils. Materials and Methods: This study was conducted on three different soil textures i.e. loam, clay loam and sandy clay loam under four slope gradients including 5, 10, 15 and 20% using factorial arrangement based on completely randomized block design with three replications in the laboratory. A flume with 0.3 m width and 4 m length was subdivided into strips of 0.1 m width and 4 m length to imitate eroding rills. Soil samples for each soil texture were passed from 8-mm sieve and packed into the flumes at its bulk density in the field. Prior to each experimental run, the soil materials were pre-wetted to reach to water-holding capacity. Tap water was introduced into the rill from the upper end, through a water supply tank and a pump at a constant flow rate of 0.5 L.min-1. After erosion, the flume was lowered to the horizontal position for the measurements of eroded rill volumes. The rill volume was determined using soil samples passed from a 2-mm sieve. Soil loss mass eroded from soil surface was computed using rill volume and original soil bulk density packed into the flume. This value was considered as estimated value using the Volumetric Replacement Method for each soil texture under different slope gradients. The performance of the method was assessed using the measured data for each soil and slope gradient using error measures such as root mean square error (RMSE) and mean absolute error (ME). Results and Discussion: Significant differences were found among soil textures and slope gradients as well as their interaction on rill erosion rate. The highest rill erosion rate was observed in clay loam (3.166 g.m-2.s-1), whereas sandy clay loam showed the minimum susceptibility to rill detachment (0.962 g.m-2.s-1). Higher fine particles (clay) and lower aggregation as well as weak aggregate stability are the major reasons for higher susceptibility of clay loam to rill erosion. The rill erosion was more sensitive to slope gradient than soil texture and the strongest dependency of rill erosion on slope gradient was found in clay loam (R2= 0.99). With an increase in slope gradient, rill erosion strongly increased except for loam. The Volumetric Replacement Method overestimated rill erosion in all soils and slope gradients. The highest overestimation was observed in sandy clay loam (RMSE= 2.72 g/m2.sec and ME= 7.02 g/m2.sec), whereas the lowest overestimation value was in loam (RMSE= 0.60 g/m2.sec and ME= 3.86 g/m2.sec). The performance of the Volumetric Replacement Method decreased in higher slope gradients and the highest overestimation was observed under 20% slope gradient (RMSE=1.86 g/m2.sec and ME= 3.84 g/m2.sec). Conclusion: Rill erosion is strongly affected by soil texture and slope gradient. Particle size distribution, aggregates percentage and their stability can control the soil’s susceptibility to detach by concentrated water flow. The Volumetric Replacement Method showed higher uncertainty as evaluated in the semi-arid soil textures especially under steep slopes. The change of soil physical properties by water flow especially bulk density result in errors in determination of rill volume by using this method. The higher change of physical properties by concentrated flow occurs in fine soil textures and steeper slopes. Additionally, continuous sedimentation along the rills imposes other errors in estimating soil loss mass from the rills.
Rasoul Mirkhani; A.R. Vaezi; hamed rezaei
Abstract
Introduction: Awareness of the physical, chemical and biological quality of soil in agriculture and natural resources is essential for optimal land management and achieving maximum economic productivity. Soil has various functions, including crop production ability, carbon storage, water retention, nutrient ...
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Introduction: Awareness of the physical, chemical and biological quality of soil in agriculture and natural resources is essential for optimal land management and achieving maximum economic productivity. Soil has various functions, including crop production ability, carbon storage, water retention, nutrient cycling, water filtering and etc. Thereby, the quality of soils can be taken into consideration depended on the purpose of their use. The soil quality indices are often regional; therefore, a set of indices cannot be used consistently to determine soil quality in all areas. In this study, the Nemero Soil Quality Index (NQI), the Weighted Additive Soil Quality Index (SQIw), and the Additive Soil Quality Index (SQIa) were determined using the total data set (TDS) and minimum data set (MDS) and the impact of properties affecting the soil quality and the yield of irrigated wheat were investigated, in Nazarabad region. Materials and Methods: This study was carried out in 26000 hectares of Nazarabad agricultural lands, known as an area with irrigated farms in western Alborz province. The Nazarabad area was sub-divided into a network consisting of 95 squires of 1650 m × 1650 m. The surface soil (0-30 cm) was sampled from the farms located in the middle of each squire (9+5 soil samples from 95 farms) and the irrigated wheat was sampled from 32 farms. Then, soil physical properties including sand, silt, and clay percentages, soil structural stability (MWD), bulk density (BD), particle density, soil porosity (F), field capacity (FC) and permanent wilting point (PWP), available water (AW), saturated hydraulic conductivity (Ks) and soil chemical properties including salinity (EC), pH, organic matter (OM), equivalent calcium carbonate (TNV), available phosphorus )p < sub>ava(, available potassium )Kava(, sodium absorption ratio (SAR) and soil microbial respiration (SMR) were measured. Effective properties on soil quality were selected using SPSS 24 by principal component analysis method (PCA). For this purpose, components with Eigen values greater than one were selected and in each component, properties with high loading coefficient up to 10% lower than the highest loading coefficient were selected MDS affecting soil quality. Then, the Nemero Soil Quality Index (NQI), the Weighted Additive Soil Quality Index (SQIw) and Additive Soil Quality Index (SQIa) were determined using TDS and MDS. For validating soil quality indices, the correlation between the yield of irrigated wheat and NQI, IQIa and IQIw indices were determined in MDS and TDS. Results and Discussion: The results showed that the correlation between the soil quality indices (NQI, SQIw and SQIa( using total data set and MDS were significant (p <0.01). In addition, a significant correlation was observed between methods of MDS and TDS in IQIw (r=0.76), IQIa (r=0.73) and NQI (r=0.68) indices. According to the results, there was a significant correlation (p <0.01) between the yield of irrigated wheat and IQIw (r=0.68), IQIa (r=0.67) and NQI (r=0.62) using MDS method; and using total data set method this correlation was 0.61, 0.58 and 0.58, respectively. The results indicated that using NQI, SQIw and SQIa indices based on MDS, 42, 57 and 57% of the study area were in very high quality category and 29, 25 and 24% were in high quality category, respectively. However, using NQI, SQIw and SQIa indices based on TDS, 16, 16 and 18% of the study area were in very high quality class and 42, 39 and 45% were in high quality class, respectively. Conclusion: The results showed that in Nazarabad region, the yield of irrigated wheat was affected by texture, p < sub>ava, B, SAR, Bd and TNV. There was no significant difference between IQIw and IQIa and NQI indices. In addition, the correlation between soil quality indices based on MDS and total data set was significant, and the correlation between the yield of irrigated wheat and the soil quality indices was stronger while using MDS rather than the use of TDS. Therefore, the use of MDS is more appropriate due to better results and fewer properties and less cost. According to the results obtained from Nazarabad region using NQI and SQIw indices, nearly 82% and 72% of the area are in the very high and high quality class, about 6% and 8% are in the moderate quality class and about 7% are in very low and low quality class, respectively. The studied area is less restricted in terms of physical properties such as soil texture and bulk density. Consequently, due to the high quality of soils in Nazarabad region, it is possible to improve the yield of wheat by proper management.
ali baliani; Ali Reza Vaezi
Abstract
IntroductionRainfall erosion results from the expenditure of the energy of falling raindrops and flowing water when these two agents act either singly or together. Soil erosion by rainfall is a serious ongoing worldwide environmental issue that contributes to soil and water quality degradation. Understanding ...
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IntroductionRainfall erosion results from the expenditure of the energy of falling raindrops and flowing water when these two agents act either singly or together. Soil erosion by rainfall is a serious ongoing worldwide environmental issue that contributes to soil and water quality degradation. Understanding raindrop-impact-induced erosion processes are key to design and apply soil management techniques that minimize and control soil erosion risk. Water erosion and especially raindrop-impact-induced erosion is the primary agents that cause soil erosion-induced degradation and has been identified as one of the major processes contributing to the soil and water quality degradation. Soil degradation caused by rainfall raindrops impacts the soil surface disperses and splashes the soil, and displaces particles from their original position. Raindrops striking the soil surface develop a raindrop-soil particle momentum before releasing their energy in the form of the splash. Other causes of soil degradation are including compaction and penetration resistance.
Materials and Methods: This study was conducted to investigate the raindrop-impact-induced erosion in relation to slope gradient (0, 10, 20, and 30%) and antecedent moisture content or AMC (air dried, quarter saturation, semi saturation, and saturation). Toward this, six soil texture classes were exposed to simulated rainfalls with 40 mm h-1 in intensity for 15-min in four slope gradients and four antecedent moisture contents. Rainfall was simulated using rainfall simulator from soil erosion laboratory of the University of zanjan with 3-meter height and surface of 2 m2. A total of 288 experimental soil boxes with 25 cm × 35 cm dimensions and 5-cm depth were investigated using the completely randomized block design with three replications. Data of soil erosion processes include splash erosion particles amount caused raindrop impact, soil resistance ratio after rainfall using penetrometer, and compaction percent using bulk density after and before rainfall was measured and then compared using Duncan's test among the slope steepness and antecedent moisture content
Results and Discussion: Significant relationships were found between the splash erosion rate, soil resistance ratio and soil compaction means (P<0.01. (The results showed that silt soil carried the highest mean value in splash erosion rate with 1574.93 gm-2 h-1, soil resistance ratio with 10.53 and soil compaction with 17.43 percent, while sand soil carried the lowest mean value in splash rate with 437.37 gm-2 h-1, soil resistance ratio with 2.66 and soil compaction with 0.25 percent. Soil erosion processes were significantly affected by slope gradient and AMC. Soil erosion processes showed a decreasing rate in 0 slope degree and increasing rate in 30 slope degree and also decreasing rate in air dried and increasing rate in semi saturation AMC. Significant correlations (P< 0.01 and 00.05) were found between soil erosion processes and sand, silt, geometric mean particle diameter, bulk density, saturated hydraulic conductivity, and calcium bicarbonate equivalent. among the physical properties of the studied soils, the sand percentage, bulk density, and Geometric mean diameter showed a negative significant correlation with splash erosion, soil compaction, and soil resistance, and the percentage of silt and calcium carbonate content with splash erosion, soil compaction, and soil resistance were positive significant correlated. The cause of this negative and positive correlation might be dependent on particles size and more percent of coarse particles, the transfer of particles from the soil mass is reduced due to raindrops and degradation processes occur with less intensity. In addition, destruction processes with more intensity occurred with increasing silt and lime percent.
Conclusion: Increasing the slope gradient has an incremental effect on the amount of rainfall erosion processes i.e. sediment load, penetration ratio, and soil compaction value. However, antecedent moisture content in various soil textures has the different effect on the amount of rainfall erosion processes. Among the soil chemical properties, only calcium carbonate equivalent with splash erosion, density, and soil surface resistance was positively correlated and chemical properties such as a percentage of organic matter and exchangeable sodium percent no significant correlated with soil erosion processes. In other words, the physical nature of soil-forming particles such as particle size, as well as some of the chemical properties of soil particles such as organic matter, have a more effect on soil degradation, density, and soil resistance ratio. also the role of soil physical properties such as sand percent and calcium carbonate equivalent on the rainfall processes were more than soil chemical properties. In general, increasing the percent of silt and lime in the soil, unlike sand, was increased the sensitivity of the soil to the rainfall erosion and as a result increasing the splash erosion leads to increased soil compaction and soil resistance ratio.
Ali Reza Vaezi; Mahdi Ebadi
Abstract
Introduction: Soil water erosion on the slope lands involves detachment, transport and deposition of soil materials due to erosive forces of raindrops and surface runoff. Surface runoff can produce relatively high soil loss and is often the dominant hillslope erosion process. The rate of surface runoff ...
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Introduction: Soil water erosion on the slope lands involves detachment, transport and deposition of soil materials due to erosive forces of raindrops and surface runoff. Surface runoff can produce relatively high soil loss and is often the dominant hillslope erosion process. The rate of surface runoff which controls surface erosion on the uniform areas in the hillsolpes, is dependent on rainfall intensity and slope steepness. In various studies, the relationships between rainfall characteristics and surface runoff were well known. Many studies have been performed on the relationship between runoff and rainfall characteristics and soil loss.The effects of slope steepness on the surface runoff and soil loss were also investigated by many researchers. In a few studies, the transportation of soil particles has been studied. For examples, some studies showed that the soil particles have different susceptibility to transport by surface flow . However, limited information is available on the effects of rainfall intensity and slope steepness on the transportability of soil particles by surface runoff in the semi-arid areas. Therefore, the objective of this study was to investigate the effects of rainfall intensity and slope steepness on the transport rate of soil particles by surface runoff in a medium soil texture in semi-arid region.
Materials and Methods: A clay loam soil with similar particle size distribution (33.15% sand, 33.22% silt and 33.63% clay) was provided to study the detachability of soil particles by surface runoff. Soil loss and particle size distribution of eroded material were determined in the soil under zero, 10%, 20%, 30% and 40% slope steepness using simulated rainfall with 10, 20, 30, 40, 50, 60, 70, 80 and 90 mm h-1 in intensity. Soil samples were filled to 32 cm 50 cm flumes with 7 cm depth and exposed to simulated rainfalls. Surface runoff, surface soil erosion and particle size distribution (PSD) of eroded material were determined in the slopes under simulated rainfalls. A total of 135 trials were carried out on 45 soil samples using the factorial completely randomized
design with three replications. Data of surface soil erosion and transportation of soil particles were compared using the Duncan's test among the rainfall intensities and slope steepness.
Results and Discussion: No surface runoff and surface soil erosion were observed in 10 mm h-1 rainfall intensity. Rainfall intensity of 20 mm h-1 appeared to be the threshold rainfall intensity to make surface runoff and surface soil erosion. Based on the results, surface runoff, surface erosion and kind of eroded soil particles were significantly affected by rainfall intensity (P< 0.001). Significant relationships were found between rainfall intensity and surface runoff (R2= 0.98) and surface erosion (R2= 0.99). Surface runoff increased strongly with increasing rainfall intensity. Increases in the rainfall intensity caused more runoff production as well as more detachment of soil surface particles . Surface runoff and surface erosion were affected strongly by the slope steepness. With an increase in the slope steepness, more surface runoff was produced and in consequence, surface soil erosion was considerably increased. Significant differences were found in the PSD of eroded material among the diffrent rainfall intensities (P< 0.001) and the slope steepness (P< 0.001). Silt showed to be the sensitive soil particles to surface erosion in rainfall intensities and slope steepness. Silt included about 66% and 74% of eroded soil particles in the rainfall intensities and the slope steepness, respectively. Sand fractions (very coarse sand, coarse sand, medium sand, fine sand, very fine sand) were the resistant soil particles to surface erosion in the rainfall intensities and the surface slopes. In higher rainfall intensities and slope steepness, more surface soil erosion was produced which was associated with the more transport of silt.
Conclusion: Rainfall intensity was the more important factor than the slope steepness in the soil loss and transportation rate of soil particles by surface runoff. Silt was the most susceptible soil particle to erosion by surface runoff in the rainfall intensities and the slope steepness. The transportation of very coarse sand and clay didn’t appear significant differences for both the rainfall intensities and the slope steepness. Protection of soil surface from raindrop impact is essential for prevention of runoff and soil loss in steep slopes especially for intensive rainfalls.
Ali Reza Vaezi; Mohammad Abbasi; Jalal Heidari
Abstract
Introduction Soil infiltration rate is the major soil hydraulic property which can be affected by the soil physical characteristics and management practices. The use of land can affect various soil properties such as physical and hydraulic properties. Differences of the hydraulic soil characteristics ...
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Introduction Soil infiltration rate is the major soil hydraulic property which can be affected by the soil physical characteristics and management practices. The use of land can affect various soil properties such as physical and hydraulic properties. Differences of the hydraulic soil characteristics such as infiltration rate in various land uses can affect their potential to runoff production as well as soil loss in the catchment. The knowledge of the physical and hydraulic characteristics of various land uses can help to better management of soil and water in the catchment. It is very essential in the semi-arid catchments where vegetation cover is generally poor, the soils are often instable against erosive factors especially when the rainfalls are consecutive and intensive. Therefore, this study was conducted to investigate the soil physical and hydraulic characteristics in the TahamChai catchment, in a semi-arid region, NW Zanjan. Various land uses consist of pastures, rainfed and irrigated lands can be observed in the catchment, which cover about 62%, 33%, and 5% of the catchment area, respectively. The pastures have been covered with poor vegetation and are intensively exhausted by over-grazing. Rainfed lands are mostly under winter wheat cultivation. Soil erosion and sedimentation were the major environmental problem in this catchment.
Materials and Methods The maps of land use and slope gradient were provided for study area. A total of 20 sites were selected based on the surface area of each land use in the catchment located between 34 46-36 53 N latitudes and 48 17-48 37 E longitudes. The study area consisted of ten sites in the pasture, seven sites in the rainfed and three sites in the irrigated lands. The geographical positions of study sites were determined by a global positing system (GPS). Soil infiltration rates were measured by double rings method at three replications in each site. Variation of soil infiltration rate was determined for each land use. Soil samples were collected at three replications from each site to determine other physicochemical soil properties. Particle size distribution, bulk density, saturation percentage, aggregate mean weight diameter, organic matter, and equivalent calcium carbonate were determined using standard methods in the lab. Mean comparisons of infiltration rate along with other physicochemical soil properties among the land uses were done using the Duncan's parametric method. The Pearson’s correlation coefficients were used to determine the relationships between soil properties and soil infiltration rate.
Results and Discussion Based on the results, no significant difference was observed between the land uses in particle size distribution. Soil infiltration rate showed different patterns among the land uses, so that significant difference was observed among them (p< 0.01). Pastures showed the lowest infiltration rate among the land uses (about 86 and 66 times lower than that of the rainfed and the irrigated lands, respectively). This result was associated with increasing soil compaction through the over-grazing in the pastures. Positive correlation was found between soil infiltration rate and aggregate mean weight diameter(r= 0.54, p< 0.05) while its correlation with bulk density was negative (r= -0.74, p< 0.01). Pastures showed the lowest organic matter content (1.35%) as well as aggregate mean weight diameter (1.12 mm) as compared with other land uses. Since the pastures are located on the steeper slopes, they have the highest intrinsic potential to runoff production and soil erosion as compared to other land uses. As a consequence, the over-grazing is the major factor of soil structure breakdown, soil compaction, and in consequence declining soil infiltration rate in the pasture lands.
Conclusion: Pastures with poor vegetation cover appeared the lowest soil infiltration capacity as compared to other land uses in the catchment. Decreasing soil infiltration rate was associated with increasing bulk density in the area. It seems that overgrazing in the pastures increases soil bulk density and leads to decline the soil organic matter content as well as soil aggregation and aggregate stability. According to the results, pastures have the highest potential to runoff production and soil erosion rather than the other land uses (rainfed lands and irrigated lands). Therefore, maintaining vegetation cover and preventing over-grazing in the catchment is recommended to increase soil organic matter content and decrease soil compaction. These practices improve the hydraulic soil characteristics especially infiltration rate and in consequence decrease the catchment potential to runoff production and soil erosion.
F. Asadzadeh; manoochehr gorji; A. Vaezi; S. Mirzaee
Abstract
Introduction: Field plots are widely used in studies related to the measurements of soil loss and modeling of erosion processes. Research efforts are needed to investigate factors affecting the data quality of plots. Spatial scale or size of plots is one of these factors which directly affects measuring ...
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Introduction: Field plots are widely used in studies related to the measurements of soil loss and modeling of erosion processes. Research efforts are needed to investigate factors affecting the data quality of plots. Spatial scale or size of plots is one of these factors which directly affects measuring runoff and soil loss by means of field plots. The effect of plot size on measured runoff or soil loss from natural plots is known as plot scale effect. On the other hand, variability of runoff and sediment yield from replicated filed plots is a main source of uncertainty in measurement of erosion from plots which should be considered in plot data interpretation processes. Therefore, there is a demand for knowledge of soil erosion processes occurring in plots of different sizes and of factors that determine natural variability, as a basis for obtaining soil loss data of good quality. This study was carried out to investigate the combined effects of these two factors by measurement of runoff and soil loss from replicated plots with different sizes.
Materials and Methods: In order to evaluate the variability of runoff and soil loss data seven plots, differing in width and length, were constructed in a uniform slope of 9% at three replicates at Koohin Research Station in Qazvin province. The plots were ploughed up to down slope in September 2011. Each plot was isolated using soil beds with a height of 30 cm, to direct generated surface runoff to the lower part of the plots. Runoff collecting systems composed of gutters, pipes and tankswere installed at the end of each plot. During the two-year study period of 2011-2012, plots were maintained in bare conditions and runoff and soil loss were measured for each single event. Precipitation amounts and characteristics were directly measured by an automatic recording tipping-bucket rain gauge located about 200 m from the experimental plots. The entire runoff volume including eroded sediment was measured on storm basis using the collection tanks. The collected runoff from each plot was then mixed thoroughly and a sample was taken for determining sediment concentration by weight. The per-storm soil loss was then obtained.
Results and Discussion: A wide range of rainfall characteristics were observed during the study period.The results indicated that the maximum amount of coefficients of variation (CVs) for runoff and soil loss from replicated plots were 60 and 80 percent, respectively, which were considerably higher than the variability of soil characteristics from these plots. CV of runoff and soil loss data among the replicates decreased as a power function of mean runoff (R2= 0.661, P
S. F. Eslami; A. R. Vaezi
Abstract
Introduction: Soil erosion by water is the most serious form of land degradation throughout the world, particularly in arid and semi-arid regions. In these areas, soils are weakly structured and are easily disrupted by raindrop impacts. Soil erosion is strongly affected by different factors such as rainfall ...
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Introduction: Soil erosion by water is the most serious form of land degradation throughout the world, particularly in arid and semi-arid regions. In these areas, soils are weakly structured and are easily disrupted by raindrop impacts. Soil erosion is strongly affected by different factors such as rainfall characteristics, slope properties, vegetation cover, conservation practices, and soil erodibility. Different physicochemical soil properties such texture, structure, infiltration rate, organic matter, lime and exchangeable sodium percentage can affect the soil erodibility as well as soil erosion. Soil structure is one of the most important properties influencing runoff and soil loss because it determines the susceptibility of the aggregates to detach by either raindrop impacts or runoff shear stress. Many soil properties such as particle size distribution, organic matter, lime, gypsum, and exchangeable sodium percentage (ESP) can affect the soil aggregation and the stability. Aggregates size distribution and their stability can be changed considerably because of agricultural practices. Information about variations of runoff and sediment in the rainfall events can be effective in modeling runoff as well as sediment. Thus, the study was conducted to determine runoff and sediment production of different aggregate sizes in the rainfall event scales.
Materials and Methods: Toward the objective of the study, five aggregate classes consist of 0.25-2, 2-4.75, 4.75-5.6, 5.6-9.75, and 9.75-12.7 mm were collected from an agricultural sandy clay loam (0-30 cm) using the related sieves in the field. Physicochemical soil analyses were performed in the aggregate samples using conventional methods in the lab. The aggregate samples were separately filed into fifteen flumes with a dimension of 50 cm × 100 cm and 15-cm in depth. The aggregate flumes were fixed on a steel plate with 9% slope and were exposed to the simulated rainfalls for investigating runoff and soil loss (sediment). Ten same rainfall events with 60 mm h-1 in intensity for 30 min were applied using a designed rainfall simulator in the lab. The rainfall simulator had a rainfall plate with a dimension of 100 cm × 120 cm which has been fixed on a metal frame with 3m height from the ground surface. Runoff and sediment samples were collected using a plastic container placed the out-let of the flumes. Runoff generation of each flume was determined based on multiplying total content volume of the tank by volume proportion of water in the sample. Soil loss for each event was determined using multiply the container volume and sediment concentration of the uniform sample. Initial soil moisture was measured in the aggregate samples before each rainfall event in order to investigate its effect on the runoff and sediment variations in the event scales. Runoff, soil loss and initial soil moisture data were evaluated for normality before any statistical analysis using SPSS version 18 software. Differences of runoff and soil loss among different rainfall events were analyzed using the Duncan's test.
Results and Discussion: Based on the results, the soil was calcareous having 16% equivalent calcium carbonate. Low amount of organic matter (0.6%). The measured aggregate stability showed to be very low, indicating high susceptibility of the aggregates to water erosion processes. Significant differences were found among the rainfall events in runoff (p< 0.05), sediment (p< 0.001) and sediment concentration (p< 0.001) which were associated with aggregate breakdown by raindrop impacts in the rainfall events. Runoff and sediment were strongly increased from each event to other event. Significant relationship was found between sediment and runoff in the events (R2= 0.89, p< 0.001). However, sediment showed to have higher increasing trend as compared to runoff variation pattern in the event scale. Sediment value was very low in the first rainfall event due to high portions of the water-stable aggregates and low level of soil moisture. Difference in runoff from each event to other event was directly related to variation of infiltration rate. In the final events, aggregate disruption was strongly enhanced and remarkably decreased the soil infiltration rate so runoff and sediment significantly increased. After seventh rainfall event, sediment production was observed to be higher (2.93 times) as compared with runoff production and in consequence sediment concentration strongly increased. The difference in the infiltration rate among the rainfall events was attributed with differences in initial soil moisture and macropores.
A.R. Vaezi; H. Gharehdaghlii
Abstract
Soil erosion prediction models are of great significance for soil and water conservation management. Rill erosion is the most important component of hillslope soil erosion processes. Therefore, predicting hillslope erosion requires that rill erosion is well understood and predictable. The study was conducted ...
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Soil erosion prediction models are of great significance for soil and water conservation management. Rill erosion is the most important component of hillslope soil erosion processes. Therefore, predicting hillslope erosion requires that rill erosion is well understood and predictable. The study was conducted to empirical quantification of rill development in the hillslopes. Rill characteristics consist of width, depth, cross section area, length, volume and soil loss, density of the rills and soil erosion rate along with slope characteristics (steepness and length) and soil properties were determined in 27 rills occurred on 9 hillslopes in marl formations of the Zanjanroud watershed, north west of Zanjan, Iran. All rill characteristics except the length showed significant correlation with both slope steepness and some soil properties including particle size distribution, sodium adsorption ratio, aggregate stability and saturated hydraulic conductivity. Rill depth as compared to other rill characteristics was reliably quantified in the hillslopes. This parameter had the highest relationship with slope steepness and saturated hydraulic conductivity (R2= 0.67, p< 0.001). Rill erosion rate contrary to the slope characteristics significantly related to clay content (R2= 0.56). This result revealed that in order to develop a model to predict rill erosion, it is vital that investigate all hillslope characteristics a long with soil properties in the watershed surface.
S. Hamidi Nehrani; A.R. Vaezi
Abstract
Marls have been recognized as susceptible formations against water erosion. Polyvinyl acetate (PVAc) is a biodegradable polymer which can be currently applied in soil conservation programs. The study was conducted to investigate effect of the PVAc on hydraulic conductivity and runoff and sediment production ...
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Marls have been recognized as susceptible formations against water erosion. Polyvinyl acetate (PVAc) is a biodegradable polymer which can be currently applied in soil conservation programs. The study was conducted to investigate effect of the PVAc on hydraulic conductivity and runoff and sediment production in a marl soil. The PVAc was applied in soil surface at five levels consists of zero (control), 50, 100, 150 and 200 kg ha-1 with three replications. The polymerized soils were putted into fifteen flumes with a dimension of 0.5m × 1m and 15cm depth. The flumes were placed in 9% slope and affected by five simulated rainfall events (40 mm h-1 in intensity and 30 min duration) with seven days interval. Based on the results, soil infiltration and hydraulic conductivity significantly affected by the PVAc application with a statistical level of 0.05 and 0.01, respectively. Analysis of runoff and sediment data showed that the runoff and sediment production was remarkably influenced by the PVAc application. There was found that 50 kg per hectare of the PVAc have the highest effect in improving infiltration rate and hydraulic conductivity, and consequently decreasing runoff and sediment production. The infiltration rate in 50 kg per hectare of the PVAc was 16.6% higher than zero treatment (control). The study reveled that the PVAc can be successfully used in the marl areas to improve soil structure and control runoff and sediment