Ehsan Ghojehpour; Vahidreza Jalali; Azam Jafari; Majid Mahmoodabadi
Abstract
Introduction Spatial and temporal variations of soil characteristics occur in large and small scales. Investigating the variability of soil parameters is considered as one of the requirements for proper management of fertilizer resources in a sustainable agricultural system. Studying of these variation ...
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Introduction Spatial and temporal variations of soil characteristics occur in large and small scales. Investigating the variability of soil parameters is considered as one of the requirements for proper management of fertilizer resources in a sustainable agricultural system. Studying of these variation is very time-consuming and costly especially in large scales. In order to the fast and reliable determination of the soil properties, various interpolation techniques have been developed and applied. The most widely used interpolation technique is the different Kriging types. The copula function is one of the new interpolation techniques that are recently used in sciences such as hydrology. Thus, the aim of this research was to evaluate the spatial variation of some soil chemical properties using the copula function and comparisons with geostatistics techniques. Materials and Methods Sampling by regular networking was done in an area of 484 ha located in 10 km far from the west of Baft city, located in Kerman province, central Iran (latitude of 29° 15′ N and longitude of 56° 29′ E). In the studied area, three agricultural, pasture and industrial sites are located nearby. The common crops of the region are wheat, barley, alfalfa, legumes and orchards of walnuts, pomegranates, almonds and grapes. The average height of the studied area is 2270 meters above sea level, the average annual temperature of the area is 16 degrees Celsius, and the average annual precipitation of the area is 247 mm. The soil used for the experiment was collected from 0 to 20 cm depth of the field. 121 soil samples were air-dried and, some physical and chemical properties were measured. In order to fit the Copula function to the data, first the appropriate marginal distribution function should be fitted to the data. For this purpose, three tests were used: Kolmogorov-Smirnov, Anderson-Darling and Chi-Square. The mentioned tests were carried out in the EasyFit 5.5 statistical software. By fitting the best marginal distribution function, the cumulative value of the marginal distribution function is calculated for each data. After calculating the above values, detailed functions can be fitted to the data. Finally, the accuracy of each interpolation method was evaluated according to the root mean square Error (RMSE), coefficient of determination (R2), mean absolute error (MAE) and mean biass error (MBE) indices. Results and Discussion In all types of geostatistical methods, the first step in interpolation is to fit the semivaiogram to the measured data, so after normalizing the data and validating the models, the appropriate model was selected for fitting the semivaiogram. Among the measured parameters, Pava and Kava semivaiogram followed spherical model and the interpolation of the above variables was done on the basis of this model. Copula analysis showed that the available phosphorous and potassium variables followed from the Wakeby and gamma distribution function, respectively. Also, based on the Pearson correlation coefficient, the correlation between pairs of points was less than 2000 m and the distance more than 2000 m was known as an independent distance. Based on the validation criteria for Pava parameter, Median copula function, Average copula function, IDW, Ordinary Kriging, Disjunctive Kriging, Universal Kriging and Simple Kriging have better estimates, respectively, and in the same way, the best interpolator for Kava parameter Median copula function, Average copula function, Ordinary Kriging, Universal Kriging, Disjunctive Kriging, Simple Kriging and IDW were determined, respectively. The estimation performance based on the coefficient of determination (R2) showed that value of this coefficient for copula function for available phosphorous and potassium were 5% and 4% greater than conventional geostatistics techniques. Also, the error of estimation was less for copula function indicating the better performance of copula to estimate the mentioned soil propertiesConclusion This study was performed to investigate the Feasibility study of Copula function in predicting some soil nutrients and comprising this method with widely used methods of geostatistics. Our results demonstrated that the copula function method is more capable than the classical geostatistical methods in estimating soil properties due to the non-dependence of this method on the normality of the data distribution and outlier data. Therefore, with the help of this method, having a reliable and high-quality data bank of soil characteristics, acceptable maps of other soil characteristics can be presented at various scales.
Saleh Sanjari; Mohammad Hady Farpoor; Majid Mahmoodabadi; Saied Barkhori
Abstract
Introduction Soil classification is a process of showing basic differences among soil classes (5). Different soil classification systems are created for soil classification, but Soil Taxonomy and World Reference Base for Soil Resources (WRB) are among the most favoured systems in the world including ...
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Introduction Soil classification is a process of showing basic differences among soil classes (5). Different soil classification systems are created for soil classification, but Soil Taxonomy and World Reference Base for Soil Resources (WRB) are among the most favoured systems in the world including Iran. This system (WRB) is accepted by soil scientists in the world and Soil Taxonomy has also been used in several countries (7). Each of the two mentioned systems has its own strong and/or weak points to show soil characteristics. However, comparing Soil Taxonomy and WRB for calcareous and gypsiferous soils of central Iran, Sarmast et al. (16) reported that according to specifiers used in WRB, this system could be more efficient than Soil Taxonomy. Various environmental conditions and its fluctuations in Kerman Province caused different soils to be formed in the province. Use of soil moisture and temperature regimes by Soil Taxonomy which is totally neglected by WRB system may emphasize that Soil Taxonomy could provide better results for these soils. That is why the present research was performed to compare Soil Taxonomy and WRB systems in the area of the present research with different climates and to show the efficiency of the two systems to describe selected soil characteristics in Kerman Province. Materials and Methods According to climatic variations, four study sites were selected in Kerman Province. Sites 1 (elevation of < 2000 m asl) and 2 (elevation of >2000 m asl) in Baft and Rabor areas were located in the south west of the province. Moreover, sites 3 (around Jiroft and Anbarabad) and 4 (around Roodbar-e-Jonoob and Ghaleganj) were located at the center and south of the province, respectively (Fig. 1). Table 1 shows the soil moisture and temperature regimes of the areas under study (3). Twenty-five pedons on different geomorphic surfaces were described and one representative pedon on each geomorphic surface (total of 11 representative pedons) were selected (Fig 1). Soil description and sampling performed (18) and the collected samples transferred to the laboratory. It is to be noticed that soil moisture regime in site 3 has changed from ustic to aridic during normal years defined in Soil Taxonomy. Ustic/ hypertermic soil moisture/temperature regimes were reported for soils of Jiroft and Anbarabad according to the soil moisture and temperature map of soils of Iran (3). However, according to the latest climatic data (30 years' data and the concept of normal years as defind in Soil Taxonomy, 2014) used in the NSM Software, the soil moisture regime was estimated as weak aridic. Results and Discussion Histic, mollic, argillic, natric, calcic, anhydritic, and cambic horizons were investigated after field work and laboratory analyses. Results of the study show that addition of new Calcixeralfs, Gypsiustalfs, and Gypsicalcids great groups together with newly added Calcic Natrargids, Calcic Natrustalfs, Gypsic Calciustalfs, Typic Petrogypsids, Anhydritic Haplogypsids, and Angydritic Petrogypsids subgroups to the Soil Taxonomy system from one hand, and addition of anhydrite and hypercalcic qualifiers to WRB from the other hand, cause a higher correlation between the two systems. Besides, climatic fluctuations of the recent years in Jiroft and Anbarabad areas caused a change in the soil moisture regime according to normal years defined in Soil Taxonomy. That is why soil name was changed in Soil Taxonomy system. However, WRB system shows no variation because this system is not related to climatic data. Since anhydritic horizon was added to Soil Taxonomy (2014) system, addition of this horizon is recommended to WRB for better correlation of the two systems as was also suggested by Sarmast et al. (16). Meanwhile, soil names in the WRB system provide more information about characteristics of young soil (including yermic qualifier to show desert pavement) compared to Soil Taxonomy.Conclusion Soil classifications showed that WRB system could describe soil characteristics in the area more efficiently compared to Soil Taxonomy. Climate change caused a variation in soil moisture regime of Jiroft and Anbarabad areas according to normal years of Soil Taxonomy system, which in turn changed soil nomenclature in this system. WRB system is not related to climate that is why soil names were not changed in the above mentioned areas. Besides, WRB system is more efficient to classify gypsiferous soils because gypsum content which is an important factor for management of gypsiferous soils is better focused by WRB. However, lack of anhydritic horizon in the WRB system is a weak point, that is why addition of this horizon was suggested by the authors. It is recommended that soil moisture/temperature regimes of study sites be calculated by softwares using climatic data because the climatic variations of the recent years might have changed the soil moisture/temperature regimes reported in the map of 1998 due to the definition of normal years defind in Soil Taxonomy.
Soil Physics, Erosion and Conservation
Ruhollah Rezaei Arshad; M Mahmudabadi; Mohammad Hady Farpoor; Majid Fekri
Abstract
Introduction Under natural conditions, intensive and erosive storms commonly associate with high-speed winds. In fact, wind velocity affects water erosion rate through enforcing falling drops and enhancing rainfall erosivity. Therefore, knowledge of interaction between wind and rain as erosive agents ...
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Introduction Under natural conditions, intensive and erosive storms commonly associate with high-speed winds. In fact, wind velocity affects water erosion rate through enforcing falling drops and enhancing rainfall erosivity. Therefore, knowledge of interaction between wind and rain as erosive agents on interrill erosion is of prime importance. However, no comprehensive study has been done on this topic under controlled laboratory conditions. This study was conducted to investigate interrill erosion affected by different rain intensities and wind velocities on several soils with different aggregate size distributions using the Simultaneous Wind-Rainfall-Runoff Simulator (SWRRS). For this purpose, a multisystem was constructed for the first time in Iran to investigate the simultaneous effects of wind and rain erosivity agents on soil erosion under laboratory conditions. Materials and Methods The simulator was calibrated in two cases. First, the intensity and uniformity of the simulated rains were assessed for each nozzle, separately. Second, the calibration procedure was performed for different combinations of the selected nozzles to achieve the best performance. For each case, different water pressures were generated to introduce several water discharges and make initial raindrop velocities. Afterwards, the interrill erosion experiment was done using four constant wind speeds including 0, 6, 9 and 12 m s-1at the height of 40 cm which were applied in combination with three rain intensities of 30, 50 and 75 mm h-1 on three soil samples with different aggregate size distributions (D2mm, D4.75mm and D8mm). Each treatment was conducted at three replicates under laboratory controlled conditions. By using different wind speeds, rain intensities and soil aggregate sizes, interrill erosion rate was measured under steady state conditions. Results and Discussion Results showed that wind velocity has a significant effect on interrill erosion rate and the interaction between wind and rain on interrill erosion was significant, as well. Although, there was no significant difference between the erosion rate at wind velocity of 0 and 6 m s-1, the wind velocity of 9 and 12 m s-1 showed significant difference with and higher erosion rates than the velocity of 6 m s-1. The mean erosion rate at wind velocities of 0, 6, 9, 12 m s-1 was 0.43 × 10-4, 0.54 × 10-4, 0.97 × 10-4 and 1.46 × 10-4 kg m-2 s-1, respectively. With increasing rain intensity from 30 to 75 mm h-1, the erosion rate increased from 0.52 × 10-4 to 1.16 × 10-4 kg m-2 s-1. On average, the erosion rate of the soil containing larges aggregates i.e. D8mm (0.73 × 10-4 kg m-2 s-1) was less than that with the finest aggregates i.e. D2mm (0.99 × 10-4 kg m-2 s-1). The findings of this study highlighted the importance and necessity of more attention to wind speed particularly those velocities faster than a threshold velocity in the study of interrill erosion. Conclusion In arid and semi-arid regions such as most parts of Iran, rainstorms are usually accompanied by strong winds. Despite the undeniable influence of wind on the erosive power of rain, a host of research has investigated water and wind erosion processes, separately. Therefore, this study was done to investigate the simultaneous effect of wind velocity and rain intensity on interrill erosion rate in three soil samples. The results indicated that wind velocity has a remarkable influence on interrill erosion rate due to wind-driven rain. Wind velocities faster than 6 m s-1 increased interrill soil erosion rate, particularly those combined with higher rain intensities. This is due to an increase in the velocity of falling raindrops on the soil surface which results in greater kinetic energy. Also, the findings showed that the soil containing coarser aggregates due to greater random roughness exhibited less sensitivity and interrill erosion rates as compared with the soil having finer aggregates, especially at faster wind velocities. The rate of interrill erosion in soil D2mm was 1.35 times higher than soil D8mm indicating the importance of random roughness. In addition, there was no significant difference between the measured erosion rates at wind speeds of 0 and 6 m s-1, in all cases. However, with increasing wind speed from 6 to 9 and also to 12 m s-1, significant increases in soil erosion rates were observed. Accordingly, a threshold wind velocity can be considered in wind-driven interrill erosion. The findings of the present study can be applied for better understanding and modeling of water and wind erosion mechanisms and dominant processes.
Soil Physics, Erosion and Conservation
Hossein Kheirabadi; Vahidreza Jalali; Hormozd Naghavi
Abstract
Introduction: The trap efficiency of sediment catcher plays an important role in the study of wind erosion and its measurements. The sediment trap efficiency generally varies with particle size distribution and wind velocity. Worldwide, wind tunnel facility has been used by many researchers to determine ...
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Introduction: The trap efficiency of sediment catcher plays an important role in the study of wind erosion and its measurements. The sediment trap efficiency generally varies with particle size distribution and wind velocity. Worldwide, wind tunnel facility has been used by many researchers to determine the efficiency of sediment samplers designed for the measurement of the deposition of Aeolian dust. Therefore, this study was conducted to investigate the efficiency of BSNE sampler, the transportability of sediment particles per wind velocity, using wind tunnel facility under laboratory conditions. In addition, a new parameter by which sediment transportability can be quantified was introduced. Materials and Methods: The wind tunnel experiments were carried out in an open circulation wind tunnel at the Soil Erosion and Conservation Laboratory, Shahid Bahonar University of Kerman, Iran. The wind tunnel consists of three sections including 1) wind generator section for producing different wind velocities, 2) test area section in which soil sample is placed and 3) sediment collector section. The wind tunnel has a uniform cross section with width and height of 80 cm by 80 cm and a total length of 12 m, with a working section of 7 m in length. The wind velocity can be varied continuously from 1 to 30 m s-1 at 40 cm height equal to 175 km/h at 10 m height. The soil used for the experiments is taken from the surface layer (0-20 cm depth) of a cultivated land from Kerman province (30 14 N and 57 06 E). The soil sample at first was air-dried, thoroughly mixed and then crushed to pass separately through 2, 4.75 and 8 mm sieve sizes in order to prepare three subsamples with different max size of 2 (D2mm), 4.75 (D4.75mm), 8 (D8mm) mm. Experiments were done as factorial based on completely random design with three replications. The factors were the height of sampler, wind velocity and soil aggregate size. Three wind velocities of 6, 10, 14 m s-1 at 40 cm height were introduced over the leveled soil surface with 7 m length and the sediment was collected using BSNE sampler at different heights of 10, 30, 50 and 70 cm at the outlet of the wind tunnel. Also, the total mass of soil loss was measured by differential weighing method for each erosion event. Results and Discussion: Results showed that the sediment flux decreased with increasing height at different wind velocities and was quantified using an exponential function, satisfactorily. The sediment transport rate near soil surface for soils D2mm, D4.75mm and D8mm ranged from 0.28 to 2.11, 0.19 to 1.06 and 0.23 to 0.65 g cm-2 min-1, respectively. This implies the soil having coarser aggregates exhibits less erodibility. Moreover, sediment flux at all heights was increased with increasing wind velocity, whereas it was reduced as soil surface roughness increased. In general, the efficiencies of the BSNE samplers varied from 53.2% to 82.1%, depending on soil aggregate size and wind velocity. The efficiency of BSNE obtained for D2mm, D4.75mm and D8mm, at wind velocity of 6 m s-1 was 61.4, 53.2 and 77.5%, at wind velocity of 10 m s-1 was 56.5, 78.7, 69.5% and at wind velocity of 14 m s-1 was 62.4, 79.1, 82.1%, respectively. Also, the results indicated that the transportability of sediment particles per wind velocity decreased with height, which was described through an exponential function. Overall, the particles in the size range of 125 to 500 micron exhibited the maximum selectivity and frequency in the sediments collected at 10 and 30 cm heights. The finding of this study revealed the high importance of vertical distribution of sediment size particles and their selectivity in wind erosion studies. Conclusion: The finding of this study indicated that most sediment particles were transported near the soil surface, this means that by appropriate conservation practices such as making sufficient roughness through this height, wind erosion can be reduced, significantly. Also, it was found the soils containing coarser aggregates due to higher random roughness show less erodibility and wind erosion rates. Finally, the efficiency of sediment sampler was found to be affected by some other factors, therefore, more attention is needed in the application of these types of samplers while the calibration is of importance, as well.
