Iranian Journal of Soil Research
Year:2001 | Volume:- | Issue:(Special Issue)|Papers Count:14

This research concerns the semi-arid area of Marvdasht in the Fars Province, south-central Iran. The area, one of the most productive in Iran, is very susceptible to land degradation due to soil, climatic, topographic, hydrological, and biological conditions. The objective of the research was to model the spatial structure of management-dependent soil properties to assess the sustainability of soil resources. Geostatistical analyses were applied to a large data set made available by the Agricultural Research Center of the Fars Province, Division of Soils. The data set included about6, 600 measured values of selected soil properties and was collected during the period of 1991- 1995, using a systematic sampling technique. Variograms of selected management dependent soil properties were computed. Based on the parameters of fitted variowams, kriging predictor was used to map the spatial characteristics of soil variables studied. All variables have large ranges of spatial dependence, indicating that long-term wheat cultivation has a homogenizing effect on dynamic soil properties. This might also be related to the lack of agrodiversity and the missing link between animal husbandry and agriculture in the area. Sampling distances smaller than the distance over which each variable shows spatial dependence; require more work without providing more information. Sampling grids with ranges of 2 km for organic carbon, 3.5 km for available phosphorus and potassium and 4 km for total nitrogen, seem to be appropriate in intensity and would be much cheaper than the undiversified, high-density sampling scheme originally applied. The parameters of the variograms, for each variable, can be used to plan efficient surveys to estimate a regional mean and variance that would maximize the information obtained from minimum sample sets. Fertilizer application zones and fertilizer recommendations can be scheduled based on the spatial variability of the soil properties. This allows fertilizers to be placed cost effectively where they will provide the most benefit.      

In this research, the 1:20,000 scales semi-detailed soil map of Gonbad-e Ghabous area in Golestan Province (Mosavati, 1986) was compared with a semi-detailed soil map, which was produced at the same scale, using a geopedologic approach. The main objective of this research was to verify the purity of soil map units. The survey efficiency in terms of time and the number of observations, which are needed to satisfactorily accomplish the field survey, was also compared. The mean values of selected soil properties in each soil map unit on the geopedologic map were statistically compared to assess soil-landform relationships. The electrical conductivity of soil extract (ECe), % clay, % silt,% sand,% CaCO3 and sodium absorption ratio (SAR) were significant at 99% probability level, indicating a strong soil-landform relationship in the studied area. The geopedologic approach led to grouping soils under 4 taxonomic orders. In contrast, only 2 soil orders were distinguished in 1986 soil surveys. More over, 13 map units and 45 map delineations were separated on the geopedologic map, while only 6 map units and 8 map delineations were differentiated on 1986soil map. The strong soil-landform relationships together with more diversity in soil map units on the geopedologic map indicate less variation in soil properties within each map unit. In other words, the map units separated on the geopedologic map of the studied area is more pure than those delineated on 1986 soil map. The geopedologic approach allows the results obtained in sample areas to be extrapolated to similar areas outside these areas. Thus, more information can be obtained from relatively lower number of identification observations at shorter time, indicating that the geopedologic approach is more cost effective than the soil survey method adopted in Iran.      

The suitability of about 8000 ha of land areas, which were mostly under cultivation in the Minab area, was evaluated. In the studied area, the soil survey studies conducted in 1970, aimed at defining the capability and limitation of the soils for irrigation, but couldn't fulfill the requirements of land evaluation studies. Therefore, the old studies were updated in an attempt to provide the land evaluation studies with recent information. Eight soil series and 50 phases were identified in the study area. On the other hand, three main crops including tomato, winter watermelon and onion were considered important for qualifying and evaluating under simple limitation and parametric (square roots method) approaches. The most limiting growth factors were salinity, alkalinity, topography and coarse fragments in soil profile, and soil depth. The obtained results of the two applied methods revealed that, most areas fall under land suitability order "S", subdividing into various land suitability classes. It was revealed that climate, as an environmental limitation factor caused about 12%decrease in crops production.      

The aim of this study was to perform qualitative and quantitative land evaluation for major crops in the Negar area. Land suitability classification was performed using a semi-detailed soil map. Limitation and parametric methods (Sys et al, 1991) as well as economic evaluation was carried out using the computer program ALES. The study area covers 1,200 ha of land about 50 km south of Kerman, the provincial capital. The information obtained from a semi-detailed soil survey indicated that Aridisols and Entisols are the main soils. In total, 9 soil families and 17 phases of families were identified. The main crops considered were winter wheat, corn, potato and sugar beet. The results of qualitative land suitability classification showed that the main factor limiting growth of the major crops in the area is soil gypsum content. The results of economic evaluation revealed that the highest gross income at high and medium management levels was gained from potato, sugar beet, wheat and corn, respectively. Comparison of the results of different methods of qualitative land suitability classification revealed that ALES is an appropriate model for land suitability classification in the study area.      

The study area is about 36,000 hectares and is located in Mianab area (Shooshtar district) in Khuzestan Province, Iran. It is between 31° 35' to 32° north latitude and 48° 50' to 49° east longitude. Based on nearest synoptic stations to the study area, the climate of the area is semiarid. The maximum daily air temperature is 46.7 °C in June and the minimum daily air temperature is 7.1 °C in December. The annual rainfall is about 325 mm. The growing period in area starts from December 4, and ends in March 10, which is about 96 days. The aim of this research was comparison of land suitability classification with different methods for finding the best methods, which suit the area. In this respect four methods were used simple limitation method, limitation regarding number and intensity of limitation, parametric method (Storie method) and parametric method (square root method). For this purpose 75 soil profiles were studied and classified up to family level, with using Keys to Soil Taxonomy (USDA, 1998). There were 20 families and 40 phases of the families. The main subgroups were Typic Ustitluvents, Typic Haplustepts, Calcic Haplusteps, Haplocalcic Haplustepts, Fluventic Haplustepts, Calcic Aquisalids and Typic Haplosalids. The results of land suitability classification show that the main soil-related limitations are salinity, alkalinity, drainage, calcium carbonate, and climate-related limitations are mean daily temperature and amount of rainfall during late season stage of growing cycle. The results of four different land suitability methods show that simple limitation method, limitation regarding number and intensity of limitation, and parametric method (square root method) are closely related, but the application of Storie method leads to a land suitability class which is one level lower, compare to other methods. Field observation demonstrated that Storie method failed giving satisfactory results in the study area. The results obtained, recommend that simple limitation method or limitation regarding number and intensity of limitation are more appropriate for qualitative land suitability classification and parametric is more accurate for quantitative land suitability classification purposes.  

The need for optimum use of land has never been greater than at present, because of very rapid population growth. Although soil survey and land classification in Iran has a rather long history, but most of the time it has been used for land suitability evaluation in order to help land developers and agriculturists. The aim of this study is soil classification, evaluation and determination of land qualitative and economic suitability for sugarbeet in Ghazvin province. The studied sites were selected based on semi-detailed soil survey report of this area prepared by "soil and water research institute". The studied area, located between 50° 1'E and 50°5 'E altitude, and 36°6 'N and 36° 13 'N longitude with 4054 ha area. Representative profiles of five soil series were studied and the corresponded samples were collected for physical and chemical and mineralogical experiments. After soil classification and experiments results, land suitability classes were determined according to " FAO system of land evaluation for special crops", with simple limitation method and parametric method. In next step, after collection of economic data including costs and income, the economic suitability classes were assessed based on gross profit per hectar for crop. The qualitative land suitability classes for sugarbeet are S2, S3 and N.      

Soils along several mountains transects in various parent materials were studied for better understanding soil genesis and determining spatial distribution of the soils over the northern slopes of Alborz Mountain Ranges (AMR). Out of 230 soil profiles, 11 were characterized at elevations ranging between 0-2000 m. The study area has an udic and a thermic/mesic soil moisture and temperature regimes, respectively. AMR with high relief: broad ridges rises to more than 4000 m in elevation, steep slopes extending in all directions, and a humid temperate climate, with decidious forest provide a wide range of soil forming conditions leading to development of Mollisols, Alfisols, Inceptisols, and Entisols. The objectives of this research were to find the relationships between soils and parent materials in order to identify map units that accurately describe soil distribution on the northern slopes of AMR. Science climate, vegetation, and time of soil formation are similar at study area, major differences in soil properties were influenced primarily by characteristics inherited from parent materials with local differences resulting from landscape position. Soil physical, chemical, morphological, and mineralogical properties inherited from different parent materials, were sufficiently different in study area which result in the clear separation of soils in to distinct subgroups with high classification accuracy. The genesis and distribution of soils are best understood when studied in landscape contexts, on uniform parent material rather than at the level of individual pedons and classification units.      

Soil genesis and classification studies were carried out on the selected soils of arid and semiarid areas of Fars Province, where calcic, gypsic and salic horizons can be found either individually or in combination. In the study areas, soils with a calcic horizon are widespread, while gypsic and salic horizons occupy smaller areas. In calcic horizons, solution followed by in situ repreciption is proposed to explain the formation of pedogenic carbonates. In gypsic horizons, bounded crystals were recognized as the major pedogenic form of gypsum. Pedogenic gypsum accumulation in these soils is presumably due to two simultaneous processes include (i) in situ solution during wet seasons / transportation / recrystalization during dry seasons; and (ii) capillary rise. The upward and downward movements of soil water caused greater accumulation of pedogenic gypsum in subsurface horizons. In some areas, where there is a high amount of gypsum in the parent material of soils, upward movement of the soluble salts from saline shallow ground water provided these soils with the characteristics of salic horizons in the gypsic horizons formed at soil surface or subsurface. In the study area the presence of relatively higher illite and chlorite confirms weak weathering condition in the soils. On the other hand, in the calcareous soils having a high amount of gypsum, formation of palygorskite can be attributed to transformation of other clay minerals as a pedogenic process.      

This research was carried out to study lime distribution in the calcareous soils of Khaveh plain located in 92 km northwest of Khorramabad, the center of Lorestan Province. The soils were derived from limestone parent materials under Mediterranean climatic condition of west Iran. The elevation of the area is 1794-2000m and mean annual rainfall and temperature are 548 mm and 10.5°C. Soil moisture and temperature regimes are xeric and mesic respectively. Relevant parent rocks are Jurassic biomicrites and biopelmicrites, Cretaceous limestones and Eocene conglomerates. Twenty-two soil profiles were dug and described through three transects, two in width and one in length directions so that all physiographic units were covered. Physical and chemical analyses were done on soil samples following common laboratory methods. The results showed that rainfall is the main factor that causes lime leaching, distribution and accumulation in lower horizons. The other factors are topography, time, irrigation water, capillary rise, water table fluctuations and wet infall of calcareous dust of atmosphere. In gentely sloping plateaux (dryland farming), the accumulation of secondary lime has occurred in the depth of 70-80 cm and lime was irregularly distributed in the soil profile (more lime in lower horizons compare to upper horizons). As the slope increases, the zone of lime accumulation moves towards the soil surface and lime distribution becomes more regular. At the head and middle of fans, the accumulation of secondary lime were not observed due to their young alluvio-collivial parent materials. At lower parts of the fans where slope decreases, secondary lime has accumulated in about 50 cm and lime distribution is irregular. In the irrigated parts of piedmont plains, there is no evidence of lime accumulation within 100cm from soil surface.      

Genesis, classification, and mineralogical characteristics of the soils of Salafchegan area in Qom province were studied and the results obtained from studying five selected pedons are presented in this paper. The soils of the studied area are mainly formed on different physiographic units with different ages (alluviall fan, upper teraces and plateaux) and are derived from eroded outcropes of Qom, Upper and Lower red formations. The poor biological activities and low to moderate leaching of lime and gypsum are the main pedological processes which have taken place in the soils of studied area, which resulted in the formation of ochric epipedon on the topsoil and accumulation of lime and gypsum in subsurface horizons. Since the parent material of the soils contain large amounts of lime and gypsum, the subsurface horizons, rich in lime and gypsum, were formed. The depth of these horizons is controlled by solubility products of these components, the age of soils and the degree of profile development. In the study area calcic and gypsic horizons can easily be identified and classified due to their stronge development. Laboratory determinations revealed that the texture of the soils ranges from coarse loamy to sandy. A reverse relationship was found between CEC, gypsum and lime. Except for soils in which montmorillonite is dominant the CEC of the studied soils, like other soils in arid and semiarid climates, is low. This is because the presences of hormite clay minerals, that have low CEC values, are common in soils. These fibrous clay minerals were probably formed as a result of pedogenic processes. Due to limitation of laboratory methods, the amount of some important parameters of the soil, such as, CEC, ESP, SAR, EC and soil texture, don't obey the expected trend found in the literature.      

Soil survey and land classification studies in Khuzestan Province, show that about 2.8 million hectares of lands are irrigated by Dez, Marum, Kurkheh and Zohreh rivers. From this area, about one million hectares are presently under cultivation and the rest have salinity and alkalinity problems. Moreover, some of the soils have saline shallow groundwater that makes these soils unutilized. After reclamation activities in the study area, the soils were grouped according to their limitations/capabilities for irrigation, but no attempts were made to determine changes in their taxonomic characteristics. The main objective of this research was to characterize and classify the soils after reclamation. The chemical and physical properties of 156 leaching tests on 55 sites, representing major soil series in the area, were studied and the soils were classified according to soil taxonomy (Soil Survey Staff 1998).