a. r. vaezi

The temporal distribution pattern of rainfall can play a role in the production of runoff and soil loss during rainfall. This study investigated four rainfall patterns: uniform, advanced, intermediate, and delayed rainfall under field conditions. The rainfall height in all rainfall patterns was 20 mm. In the uniform rainfall pattern, a constant rainfall intensity (40 mm h-1) was used and in the non-uniform rainfall patterns, a maximum rainfall intensity of 40 mm h-1 was applied for a 15-minute duration. The experiments were carried out in 60 cm × 80 cm plots on a hillslope with a slope gradient of 9% at three replications. Rainfall patterns were set up on the plots in five events with an interval of one week. The results showed a significant difference between rainfall patterns in runoff and soil loss (p<0.01). This difference was due to the destruction of surface soil structure and the reduction of water infiltration rate, especially during peak time of rainfall intensity (40 mm h-1). The highest runoff occurred in the delayed rainfall (3.43 mm) while, the highest soil loss (61.47 g m-2) was observed in the intermediate rainfall, which was associated with the peak intensity of rainfall at the end of the rainfall and its role in the destruction of the soil structure on the one hand, and the loss of infiltration rate on the other hand. Variation of runoff and soil loss from one event to another indicated that soil loss is in line with runoff production in uniform rainfall, while soil loss did not follow runoff in other rainfalls. Soil loss in these rainfalls was affected by both runoff production and availability of erodible soil particles. These results revealed the necessity of studying the rainfall intensity distribution pattern for accurate prediction of soil erosion and determining soil loss variation event by event in the semi-arid region.

Water erosion can be affected by land use change and soil degradation by agricultural activities. This study was conducted to investigate the effects of land use change in poor pastures on soil physical degradation and water erosion in semi-arid regions. Experiments were performed in 42 soil samples taken from seven areas covering the two land uses: poor pasture and rainfed agriculture, which have different soil textures (clay loam, silty clay loam, sandy clay loam, silt loam, loam, sandy loam, and sandy loam). The physical characteristics of soils were measured in the samples of both types of land use and its changes were expressed as physical degradation of the soil. The soil's susceptibility to water erosion was measured under simulated rainfall with 50 mm h-1 intensity for 60 min. The results showed that the land use change in pastures leads to the physical deterioration of soils; so bulk density, porosity, macropore, field capacity, saturated point, aggregate size, and aggregate stability were degraded with a rate of 28, 22, 41, 11, 5, 62, and 63 percentages. The structural characteristics of soil (aggregate size and stability) had the highest physical deterioration due to the land use change in the pastures. The change in land use change greatly increased the sensitivity of soils to water erosion. A significant relationship was found between the susceptibility of water erosion and the soil's physical degradation. The soils with coarser and more stable aggregates have higher physical degradation by the land use change and in consequence show more susceptibility to water erosion.

Improving soil physical properties and increasing water retention in the soil are management strategies in soil and water conservation and enhancing crop yield in rainfed lands. This study was conducted to investigate the role of tillage direction and wheat stubble mulch level in improving soil physical properties in rainfed land in Zanjan province. A field experiment was done at two tillage directions: up to the downslope and contour line, and five stubble mulch levels: zero, 25, 50, 75, and 100% of land cover equal to 6 tons per hectare. A total of 30 plots (2 m×5 m) were created. The results indicated that water infiltration and water content were considerably affected by tillage direction, whereas its effect on water holding capacity was not significant. This physical property of the soil was influenced by the inherent properties of the soil, including particle size distribution. The change of up to down tillage direction to the contour line increased soil infiltration to 11% and water content to 6%. The physical soil properties were wholly influenced by mulch consumption. Soil water content increased in mulch treatments along with water holding capacity and infiltration rate. The highest volumetric water content was at 100% mulch level (10.62%) which was 11% more than the control treatment. However, there was no significant difference between 100% and 75% mulch treatment. This revealed that the application of 75% stubble mulch in contouring tillage is a substantial strategy for improving soil physical properties and controlling water loss in rainfed lands of semi-arid regions.

 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.
 

 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 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.
 

 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.

This study was conducted to investigate the temporal variations of runoff and rill erosion in various soil textures under different slope gradients. So, a laboratory experiment was set up in three soil textures (loam, clay loam, and sandy clay loam) and four slope gradients (5, 10, 15, and 20%) using the completely randomized design with three replications. Runoff production and rill erosion were measured at a flume with 4 m×0.32 m in dimensions using a simulated water flow with 0.5 lit min-1 in discharge during 30 min. Results indicated that runoff and rill erosion and their interaction were significantly affected by soil texture and slope gradient (P < 0.001). Significant relations were found between rill erosion and runoff both in three soils and four slope gradients, and the strongest relations were in loam (R2= 0.86) and 15% slope gradient (R2= 0.94). Runoff and rill erosion varied considerably in the soil textures and slope gradients during the experiment. A 10-min pick time was found for runoff and rill erosion. In contrast to runoff, rill erosion appeared an irregular and gradual increasing pattern during the experiment which was associated with the frequency of transportable soil particles. Clay loam had more sensitive particles due to a higher percentage of fine particles and weaker structure, and most of them were washed in early times, and finally, rill erosion was reached to a constant pattern. This study revealed that temporal variation patterns of runoff and rill erosion are influenced by soil type (texture and structure) and slope gradient.

Soil moisture (SM) acts like an impressive factor in hydrological process, agricultural productivity and monitoring of dangerous outcomes of climate change. The main purpose of this study was to monitoring and pattern recognition of spatial and temporal variation of SMAP soil moisture in five subcatchment of Simineh-Zarrineh catchment in north west of Iran from 2015 to 2017. Precipitation data of thirty-five meteorological stations and 287 soil moisture points derived from the SMAP were used to monitoring SM variations in the time scale. Result indicated that the SM variations are subject to precipitation variations throughout the monthly scale in the catchment. In all seasons of the period SM decreased from north to south of the catchment also on the contrary, east to west does not follow up such a constant pattern. Oscillation SM patterns in this time period were completely coordinated by precipitation pattern. The determination coefficient between monthly SMAP soil moisture and precipitation for each sub-catchment was 0.9, 0.83, 0.7, 0.84 and 0.71 for Bokan, Saqqez, Takab, Saeinqaleh and Miandoab sub-catchment, respectively. Spatial variability of standard deviation for SM values was used to find the amount of deviation from the average value during dry and wet seasons. Result reveal that in seasonal scale northwest (0.067 to 0.069 cm3.cm3) and east parts (0.057 to 0.061 cm3.cm3) of study area have higher values of the SM standard deviations in autumn. Results demonstrated that high value of standard deviation was observed in autumn season because of irregular precipitation events and fluctuation of temperature.

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.

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).

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).

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.

Soil Temperature (ST) is critical for environmental applications. While its measurement is often difficult, estimation from environmental parameters has shown promise. The purpose of this study was to model ST in cold season  from soil properties and environmental parameters. This study was conducted as a pot experiment in Ardebil, Iran. Automatic thermal sensors were installed at 5 and 10 cm depths. Besides, soil properties and environmental parameters were determined based on field and laboratory works. Machine learning methods including Multiple Linear Regression (MLR), Artificial Neural Network (ANN), and Adaptive Neuro-Fuzzy Interface System (ANFIS) were used for modeling ST. The air temperature was observed as the most effective factor in ST modeling. The relationship between soil and air temperature was stronger at 5 cm depth compared to 10 cm. The R2 between soil and air temperature was higher in the absence of sunlight than in its presence. The prediction of ANFIS (R2= 0.96 and MAPE= 10.5) was closer to the observed ST values compared to the ANN (R2= 0.91 and MAPE= 35) and MLR (R2= 0.57 and MAPE= 41). The results revealed the advantage of ANFIS method for ST modeling. This approach can be applied for soil depths and locations with data gap.

This study aimed to investigate the effect of soil physicochemical properties on gully erosion in the Qarranqou Chai watershed located in the south of East Azerbaijan province. Toward this, a rainfed area with 30 km × 30 km in dimensions and affected by gully erosion was selected in the area and gully erosion, morphological characteristics of gullies along with physicochemical soil properties were determined in each grid. Results indicated that gully erosion is ranged from 2.64 to 242.7 ton per square kilometer, with an average of 21.38 ton per square kilometer. It is significantly correlated with sand (r= 0.28), moisture saturation percentage (r= 0.27) and aggregate stability (r= -0.29). Aggregate stability in contrast with two other soil properties appeared negative role in gully formation. No significant correlation was found between gully erosion and silt and soil erodibility factor (K) estimated by the Universal Soil Loss Equation (USLE). This study revealed that aggregate stability is a major soil properties controlling gully erosion in rainfed lands. Maintaining crop residues is the first strategy to enhance soil organic matter content, improve aggregate stability and in consequence decrease the soil’s susceptibility to gully erosion in the area.

This study was conducted to investigate the capability of the Universal Soil Loss Equation (USLE) and its versions (RUSLE, USLE-M and AUSLE) models in predicting soil loss at the plot scale in a semi- arid region in Zanjan. Toward this, twenty two plots from 1m to 22.1m with the same widths (1.83m) were installed on a uniform slope 10 percent. The plots were maintained under the USLE standard plot conditions for a fourteen-month period (from March 2013 to Jun 2014). Based on the results, an increasing trend was observed in soil loss with increasing plot length from 1 m (0.01 ton/ha.year) to 6 m (0.07 ton/ha.year), which was associated with increasing runoff and its transport capacity. Mean estimated soil loss using the USLE, RUSLE, USLE-M and AUSLE for twenty two plots was 80.2, 65.4, 4 and 113.5 times bigger than the measured values, respectively. The USLE-M appeared the lowest error in soil loss estimation as compared to other two models. In this model, erosivity factor is determined using runoff along with rainfall characteristics. This study revealed that the calibration of the empirical soil erosion models using long period data is essential for predicting soil loss in the plot scale.

In semi-arid regions, soils are weakly aggregated and subjected to water erosion processes especially rill and interrill erosion. There is no information on the rate of these water erosion types in semi-arid soils located in the hillslopes. Therefore, this study was conducted to determine the soils susceptibility to these erosion types in semi-arid region. A laboratory experiment was done in eight soil textures using in a 0.6 m × 1 m flume a simulated rainfall with 50 mm.h-1 in intensity for 60 min. Rill and interrill erosion rate was measured using soil loss amount per flume area and rainfall duration. Based on the results, both rill and interrill erosion rate were significantly varied among the soils textures (P<0.001). Silt loam was the most susceptible soil to rill erosion (0.22 g m-2 sec-1) and interrill erosion (0.15 g m-2 sec-1), whereas sand didn’t appear any soil loss by these water erosion types. The compression of soil loss resulted by rill and interrill erosion among the soil tectures showed that rill erosion rate for sandy clay loam, silt loam, loam and sandy loam was 3.2, 1.4, 1.1 and 2.8 times higher than interrill erosion rate, respectively. These differences were statistically significant. Silt content was the major factor controlling soil loss difference in these soils. This study revealed that the study semi-arid soils having higher silt content appears also higher rill erosion rate than interrill erosion rate.

In arid and semi-arid regions such as Iran, water shortage and soil absorbable nutrients deficiency are limiting factors of plants growth. Nutrient deficiencies are compensated by chemical fertilizers. The main issue in fertilizer consumption is to use the optimal amount of fertilizer that increases water and fertilizer use efficiency. One of the newest and most effective approach for efficient use of water in agriculture is to magnetize the irrigation water. For producing magnetized water, it is crossed through a permanent magnetic field. By crossing water through a magnetic field, its physical and chemical properties improve. The aim of current research was, investigating the effect of urea fertigation by magnetized water on yield, water and fertilizer use efficiency in cucumber cv. Kish F1.

This study was performed as split plot experiment based on completely randomized block design with three replications from June to November 2018 on cucumber cultivate Kish F1 at the Research Farm of Agricultural Faculty, University of Zanjan, Iran. The treatments consisted nitrogen fertilizer levels at 5 levels from urea source (0%, 25%, 50%, 75% and 100% crop fertilizer requirement) and irrigation water (magnetized and no magnetized water). The treatment of 0% urea fertilizer and no magnetized water were considered as control. For crops irrigation, tape-drip irrigation system was used and for magnetizing of water, an electromagnetic field with 0.1 tesla was used. The crop water requirements were calculated by FAO-Penman-Monteith Approach on a daily basis using on-time weather parameters data of Zanjan Station. The irrigation frequency was 3 days. During the growth period, fertilization was done as fertigation approach on four times (15%, 30%, 30% and 25% of total crop urea fertilizer requirement). The first fertilization was applied 45 days after planting and the rests was carried out as 10-day periods after first fertilization.

The effect of urea fertilizer levels were significant at 0.1% level on yield, water use efficiency, number of fruits and leaf area, at 1% on chlorophyll index and at 5% on fertilizer use efficiency. Magnetized water was significant at 0.1% level on the all evaluated traits, except chlorophyll index. Treatment interaction effects were significant on water use efficiency, urea fertilizer use efficiency and number of fruits at 1% and no significant effect on the rest of traits. Compared with control, the highest and lowest increase in mean chlorophyll index were in 75% and 0.0% urea fertilizer level and magnetized water (21.1% and 0.4% respectively). At any urea fertilizer level, mean leaf area in magnetized water treatment was greater than no magnetized water treatment. Maximum and minimum difference between magnetized and not magnetized water treatments were in 25% and 0.0% urea fertilizer level (155.8 and 143.6 cm2, respectively). Based on treatments interaction, maximum mean of fruits number, achieved in 75% urea fertilizer level-magnetized water (32.8 number). It was 47.7% more than control. Maximum mean of cucumber yields with 50.3 t/ha, were in 75% urea fertilizer level-magnetized water that it increased 17.9, 2 and 3.8 t/ha compared with control, 100% urea fertilizer level-magnetized and no magnetized water, respectively. Results showed that application of magnetized water to irrigate plants, increased water use efficiency. Maximum water use efficiency achieved in 25% urea fertilizer level and magnetized water as much as 17.7 kg/m3. The trend of variations in mean water use efficiency showed, in no magnetized water, by reducing the application amount of urea fertilizer, averages of water use efficiency decreased but in magnetized water treatment, the trend of variations were incremental from 100% to 75% urea fertilizer level. On results, at each level of urea fertilizer treatment, using magnetized water for plant irrigating, increased mean of fertilizer use efficiency compared no magnetized water treatment. Maximum difference between means of urea fertilizer use efficiency at magnetized and no magnetized water was achieved in 25% urea fertilizer level as 74.3 Kg/Kg (367%). The results also showed, the trend of variations in mean urea fertilizer use efficiency at no magnetized water were decreasing from 100% to 25% urea fertilizer level but at magnetized water, the trend was increasing.

based on results of the current research, the optimum urea fertilizer level in Zanjan Region for cucumber is 75% urea fertilizer requirement, which by applying magnetized water to irrigate cucumber plants, mean of yield increases. In this case, in addition to save 25% of urea fertilizer amount, it is also prevented environmental problems.

Study of factors that affecting soil erosion and its temporal variation is prerequisitethe for management of soil and water resources. The purpose of This study was to determine susceptibility of soils to erosion and its temporal variations in three soil textures (clay loam, loam and sandy loam) on different slopes (5, 10, 15, 25, and 30 degree) under simulated rainfalls (40, 60 and 80 mm h-1). The experiment done by flume (160 cm × 65 cm) and in a completely randomized design with two replications. Soil losses measured at various times (0/5, 1, 1/5, 2, 3, 4, 5 10, 15, 20, 30, 40,50 and 60 minutes) to achieve steady-state flow of surface runoff. There was a Significant difference between  the soils in  terms of soil loss (p< 0.01). Clay loam was the most susceptible on to soil erosion. In this soil, Most of erodible soil particles eroded by surface runoff at the beginning of rainfall and soil loss decrese with continuing of rain. Soil loss in soils was strongly influenced by slope gradient and rainfall intensity (p< 0. 01). by increasing slope gradient,due to lower rain water retention on the surface, runoff was occurred quickly, and then soil loss increased. in soil loss of sandy loam,Slope steepness and rainfall intensity showed dominant roles in soil losses. The results revealed that in erodible soils, sensitivity to erosion by changing the slope and rain intensity is lower, and these two factors (slope steepness and rainfall intensity) has greatest impact on soil loss in highly resistant soils to erosion .

Rill erosion is one of the most important types of water erosion in semiarid dry land areas. The importance of this study is more in the soils of semi-arid regions, similar to many parts of Iran, which have unstable soil aggregates. The aim of this study was to investigate the role of raindrop impact on the size distribution and homogeneity of sediment particles in rill erosion of soils with different textures. Therefore, the effect of raindrops on changes in the size distribution of sediment particles was determined in rills of 4 meters in length and 0.10 meters in width under rainfall simulated with a constant intensity of 90 mm h-1 in different slope gradients (5%, 10%, 15%, and 20%) in 12 soil texture classes. Experiments were carried out in two soil surface coverconditions including with raindrop impact (bare soil) and without raindrop impact (use plastic net), and the effect of raindrop impact on the variables was determined. The experiment was conducted in four replicates with a total of 352 experimental units. The study of this subject using the particle size distribution curve showed that there was a clear difference between the curves in the two soil surface cover conditions. The sediment particles size distribution curves were below the original soil particles size distribution curve, suggesting an increase in the mean diameter of the particles in sediments and an increase in the transport of coarse particles such as sand at the end of the experiment. The increase in geometric standard deviation in the sediment was strongly dependent on soil texture and slope and, contrary to the expected, homogeneity of sediment particles was not significantly affected by the removal of raindrop impact, and by increasing the slope in all soil texture classes, sediment particles heterogeneityincreased, likely due to increase in flow velocity and flow power. The highest non-homogeneity of sediment particles was observed after precipitation in silty soil.

Rills are often the major area and source of runoff and sediment in hillslopes. The hydraulic characteristics of flow in the rills can be affected by type and amount of sediment. Knowledge on the flow hydraulic characteristics is essential to find the major mechanism of rill development. The objective of this study was to evaluate the effects of type and amount of sediment on the rill hydraulic characteristics. Laboratory experiments were carried out in a flume with 4m× 0.4 m×0.3m dimensions located at 9% slope steepness under 90 mm h-1 rainfall intensity which was applied on three soil textures of loam, loamy sand and sandy clay loam with four replications. Reynolds number, Froude number, flow depth, Darcy–Weisbach friction coefficient, shear stress and stream power were determined during the rill erosion process. The results showed that Reynolds number and Darcy–Weisbach friction coefficient increased as the sediment load increased in the rills. Froude number decreased as sediment load increased which was attributed with decreasing flow velocity. Shear stress and stream power and flow depth increased with increasing the eroded sediment. Flow depth increased with incease of sediment load, varying from 0.041 to 1mm in loam soil, 0.07 to 1.3 mm in loamy sand soil and 0.06 to 0.7 mm in sandy clay loam soil. Coefficient of determination between sediment load and all hydraulic characteristics were higher than 90% for loam and loamy sand and higher than 60% for sandy clay loam. This study revealed that significant interaction was between sediment load and hydraulic characteristics of flow in the rills.

For zoning of wheat grain yield, simple kriging, cokriging and regression- kriging methods were evaluated. For this purpose, in 2014, 298 rainfed wheat fields with distances of 0.59 km from each other were selected at the Khodabandeh county located in the south of Zanjan province. Wheat grain yield of the rainfed lands was measured using the quadrant plots in the field. Soil samples were collected from the surface soil (0-30 cm) of the fields at two replicates. Physical and chemical properties of soil including sand, silt, clay, moisture, organic matter, pH, EC, calcium carbonate equivalent, total nitrogen, available phosphorus and plant-available potassium were measured. Soil data were used to assess the geostatistical models and evaluate the soil characteristics roles on wheat grain yield over the fields. Out of total data, 238 data were used to develop geostatistical models and 60 data were applied to test the models. Results showed that cokriging estimated wheat grain yield in new locations more accurate (R2= 0.74, RMSE= 118.95) than the simple kriging (R2= 0.74, RMSE= 127.87) and regression- kriging (R2= 0.26, RMSE= 198.84). Soil total nitrogen was used as auxiliary variable in cokriging method to determine the spatial variation of wheat grain yield. In addition, according to the results by understanding the spatial variation of the soil total nitrogen spatial grain yield variation can be quantified and used as geostatistical map for management scopes.

Runoff coefficient can be used as a measure for assessing the flood generation potential of the watersheds. This factor is depending on the watershed characteristics and may vary temporally during a year. Knowledge on the watersheds with higher potential to runoff production and determining pick time of runoffs is essential for designing watershed management practices in an area. In this study, physical characteristics with rainfall and runoff data for a thirty-year period (1986-2010) were studied in eleven forth order watersheds in Ardabil, Iran. The watersheds surface areas vary from 257 to 2184 km2 and their slopes are between 16.25% and 33.3%. Significant differences were found among their monthly rainfall (p

Marls are the most susceptible geological formation of erosion and keeping a permanent crop cover on the soil of this formation is difficult due to some limitations such as the instability of soil
structure, poor soil productivity and low soil moisture storage. Polymers can be investigated as one of options to protect soil resources in these formations. This study was conducted to compare the effects of polyacrylamide (PAM) and polyvinyle acetate (PVAc) on improving soil properties and germination rate in the marl formations. PAM and PVAc were sprayed on the soil surface with 0.0, 33.3, 66.6, 100.0 kg ha-1 amounts in three splits. In total 32 boxes of polymerized soil were provided and wheat seeds were planted in them. The soil physical properties along with the wheat germination percentage were evaluated in the polymerized soils after five rainfall simulations (40 mm h-1 for 30 min). The experiment was conducted as factorial using a completely randomized design with three replications. With an increase in the two polymers rates, aggregate size, aggregate stability and saturated hydraulic conductivity were significantly improved whereas bulk density and soil surface resistance were strongly decreased in the prepared marl soil. Water holding capacity and available water of the soil decreased after the application of PAM while no significant differences were found after treating with the PVAc. This study revealed that the PVAc had the same role with the PAM in improvement of soil physical properties and in contrast it had no negative effect on the water holding capacity. Therefore, the PVAc can be successfully considered as a replacement for the PAM in the marl areas.

Aggregate stability is one of the most important soil physical properties which can affect the soil disruption by raindrops. This research was conducted to study the aggregates breakdown under raindrops impact and its relationship with aggregate stability in some semi-arid region soils of Zanjan province، Iran. Thirty soils samples with three replications were taken from thirty dry-farming lands at North West of Zanjan in 2011. Aggregate samples with diameters of 6-8 mm were taken from each farm soil and put in a flat box with dimensions of 24 cm × 30 cm and 6-cm depth. The soil boxes were separately affected by four simulated rainfall events with intensity of 60 mm h-1 for 30-min duration. The amount of aggregate breakdown in each soil box under each rainfall event was then determined by comparing of the mean weight diameter (MWD) of soil aggregates before and after each rainfall event. Aggregates stability was determined using two wet-sieving and water-drop test. Results indicated that the amount of aggregate breakdown on the basis of MWD values significantly varied among 30 soil samples (p£ 0. 001)، due to rainfall impact. Aggregate breakdown had no significant correlation with the aggregate stability determined using the wet-sieving method، whereas it was negatively correlated to the aggregate stability obtained based on the water-drop test method (R2= 0. 29، p£ 0. 05). Aggregate breakdown in the soils was significantly related to geometric mean diameter of mineral particles، gravel and organic matter (R2= 0. 65، p£ 0. 001).

Rill erosion is the detachment of soil particles by scouring and transport of sediments by a concentrated water flow on the hillslope. It plays an important role in soil loss on the hillslope. Various soil properties affect its resistance to rain drops impact and runoff shear stress، and consequently they influence rill erosion. The study was conducted to determine rill erosion and its temporal variation during rainfall in different soil textures. Simulated rainfall experiments were performed in eight soils (clay، clay loam، sandy clay loam، loamy، silty loam، sandy loam، loamy sand and sandy) at the plots (1Í 1. 2 m) installed in a hillslope. The plots were exposed to five simulated rainfalls with an intensity of 60 mm h-1 for 60-min. Rill erosion variation during each rainfall was determined by collecting sediment in a storage tank at the outlet of the plots. Results indicated that rill erosion was strongly affected by the soil texture (p ≤ 0. 01). The highest and the lowest rill erosion were observed in clay (322 g m-2) and sandy soil (zero)، respectively. Rill erosion rate was associated with water infiltration rate and transportability of particles in the soils. Rill erosion rate increased during the rainfall event due to disruption of soil aggregates and runoff generation. In the soils rill erosion rate rapidly increased at early times and finally reached a relatively constant level. The loamy soil showed lower variation in rill erosion rate than other soils due to greater resistance to soil erosion.

Water has a vital role in increasing crop yield in dry farming lands in semi-arid regions. This study was conducted to determine factors affecting runoff and develop an equation for predicting the runoff in the dry farming lands. The study was conducted in the Hashtroud, located in south part of East-Azarbijan province in northwestern Iran, from March 2005 to March 2006. A square network of dry farming lands with 900 km2 area was selected and divided into 36 regular grids with a dimension of 5 km. In each grid, runoff plots with dimensions of 22.1 m in length and 1.83 m in width at three replicates and 1.2 m spacing were prepared on a dry farming land with a slope 9%. At the lower parts of the plots, runoff-collecting equipments were established. Rainfall properties were determined on the basis of recording rain gauge data of a meteorological station. Based on results the runoff in the plots was affected by 23 natural rainfall events during the study period. The soils of the study area are mainly clay loam with a moderate infiltration rate and having almost 1% organic materials and 13% lime. Runoff amount per rainfall event varied frame 2.153 to 49.377 liter per plot. Runoff negatively correlated (r= -0.85, p<0.001) with soil infiltration. The results indicated that the runoff can be easily predicted using a linear regression equation based on coarse sand, organic matter and lime (R= -0.84, p<0.001). Coarse sand, organic matter and lime significantly increased soil infiltration and consequently reduced runoff.

In the Universal Soil Loss Equation (USLE), soil erodibility factor K can be estimated by using a regression equation that has been presented based on field erosion plots in relatively non-calcareous soils. Therefore, it seems necessary to determine the estimating error of the regression equation in calcareous soils of Iran. This study was conducted in an agricultural area with a dimension of 30 km in Hashtrood province, northwest of Iran during March 2005-2006. The studied soils had about 1.1% organic matter and 13% lime (TNV). In order to investigate the soil erodibility, 36 regular grids of 5×5 km were considered on the study area. On each grid, three standard plots with 1.2 m intervals were established in dryland farming area having a 9% south hill slope. The actual soil erodibility value of the plots was determined as the annual soil loss per annual rain erosivity factor under natural rainfall events. The K value was estimated using the USLE regression equation. Soil physical and chemical properties were measured in samples taken from 0 to 30 cm depth. The results indicated that mean actual value of the soil erodibility factor in the study area was 0.004258 Mg.h.MJ-1.mm-1 which is 10.75 times smaller than the estimated K-factor. There was a poor correlation (R2= 0.16) between the actual and estimated soil erodibility factor. The estimating error values of the soil erodibility varied from 3.173 to 39.298 with a mean error of 9.984. There was a significant correlation between the calcareous soil erodibility and the amount of coarse sand, silt, organic matter and lime (TNV) of the soil. Regression analysis showed that the calcareous soil erodibility significantly (R2= 0.80, p)