Yaser Safari; Mohammad Amir Delavar; Zahra Noori
Abstract
Introduction: Land suitability evaluation (LSE) may be considered as a worldwide accepted procedure to achieve optimum utilization of the available land resources for sustainable agriculture. The common LSE procedures, like the widely accepted “A framework for land evaluation” presented by FAO, however, ...
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Introduction: Land suitability evaluation (LSE) may be considered as a worldwide accepted procedure to achieve optimum utilization of the available land resources for sustainable agriculture. The common LSE procedures, like the widely accepted “A framework for land evaluation” presented by FAO, however, do not consider variability of soil quality parameters; whereas, the soil quality and its suitability for different uses are influenced by highly variable land management strategies. Therefore, assessing the spatial variability pattern of environmental variables and their accumulative effects on land suitability for specific crops, is the key for achieving to thoughtful land use planning for sustainable use. The present study was done aimed to evaluation of spatial variability of land suitability for irrigated wheat in Zanjan plain using accumulated limitation scores and geostatistics.
Materials and Methods: The study area is located in the southern part of Zanjan city, northwestern Iran, between the latitudes 36° 33′ and 36° 40′ N and the longitudes 48° 23′ and 48° 37′ E, covering an area of about 7000 ha. A total of 85 sampling locations were designed using a systematic sampling grid with an interval of 1000 m and consequently, soil samples at all sampling sites were collected from the depths of 0–25, 25-50, 50–75 and 75–100 cm. The soil samples were taken to the laboratory, where they were air-dried and then passed through a 2 mm sieve. Prepared samples were subsequently analyzed for required soil properties in LSE (Sys et al., 1993) using standard methods. Besides, required climatic data for LSE were obtained from Znajan Synoptic Meteorological Station for a 50 years period (1961– 2011). Then, the limitation degrees for all of the important properties for wheat cropping were determined (Sys et al., 1993). Afterwards, the determined limitation degrees were converted to limitation scores using standard tables presented by Zhang (1989). Then, accumulated limitation scores were calculated for all locations and using an exponential equation, land-suitability membership scores were achieved. Finally, these scores were interpolated using ordinary kriging method in ArcGIS software (ver. 10.2; ESRI) and the final suitability map was produced.
Results and Discussion: The results showed that the climatic conditions for irrigated wheat was relatively good; so that the region received just 1 limitation score arisen from the mean temperature of the growing cycle. On the other hand, among the studied soil properties, the content of coarse fragments made some serious limitations for wheat farming in the studied area; so that more than half of sampling points showed moderate to very severe limitations in respect of this property. This high observed limitation of coarse fragments may be attributed to the youthfulness of studied soils; because according to Soil Taxonomy, the studied soils are mainly classified as Entisols, which are poorly developed and immature soils maintaining their rock structure to some extent. Other studied soil properties, like soil texture and calcium carbonate equivalent content, made no or slight limitations for wheat farming in the studied soils. Accumulated effects of limiting properties led to elevated limitation scores in some sampling locations, especially in northwestern parts of the area and consequently, their suitability classes were decreased. Attributing the specific land suitability classes to each sampling location based on the calculated limitation scores revealed some sharp variability in suitability classes thorough the relatively small distances, which seems to be less compatible with the widely accepted generality of soil continuity. Totally, the spatial distribution map of land-suitability membership scores showed appreciable variability thorough the area. This may suggest that the studied soil properties have relatively high short-range variations, which is originated from the soil substantial characteristics or management practices. Comparison of the interpolated suitability map with the point map revealed that the spatial variability pattern of land suitability for irrigated wheat was more gradual and more obvious in interpolated map.
Conclusions: Compared with common conventional land suitability procedures, continuous pattern of land suitability variation based on the fuzzy viewpoint to the soil variability, lead to more compatible results with the continuous nature of environmental variables. However, due to the long and short-range variations of various soil properties thorough the studied area, appreciable variations in land suitability for wheat farming was observed. Controlling this highly variable suitability of studied lands for irrigated wheat farming needs precise and thoughtful management strategies.
M.A. Delavar; Y. Safari
Abstract
Introduction: The accumulation of heavy metals (HMs) in the soil is of increasing concern due to food safety issues, potential health risks, and the detrimental effects on soil ecosystems. HMs may be considered as the most important soil pollutants, because they are not biodegradable and their physical ...
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Introduction: The accumulation of heavy metals (HMs) in the soil is of increasing concern due to food safety issues, potential health risks, and the detrimental effects on soil ecosystems. HMs may be considered as the most important soil pollutants, because they are not biodegradable and their physical movement through the soil profile is relatively limited. Therefore, root uptake process may provide a big chance for these pollutants to transfer from the surface soil to natural and cultivated plants, which may eventually steer them to human bodies. The general behavior of HMs in the environment, especially their bioavailability in the soil, is influenced by their origin. Hence, source apportionment of HMs may provide some essential information for better management of polluted soils to restrict the HMs entrance to the human food chain. This paper explores the applicability of multivariate statistical techniques in the identification of probable sources that can control the concentration and distribution of selected HMs in the soils surrounding the Zanjan Zinc Specialized Industrial Town (briefly Zinc Town).
Materials and Methods: The area under investigation has a size of approximately 4000 ha.It is located around the Zinc Town, Zanjan province. A regular grid sampling pattern with an interval of 500 meters was applied to identify the sample location, and 184 topsoil samples (0-10 cm) were collected. The soil samples were air-dried and sieved through a 2 mm polyethylene sieve and then, were digested using HNO3. The total concentrations of zinc (Zn), lead (Pb), cadmium (Cd), Nickel (Ni) and copper (Cu) in the soil solutions were determined via Atomic Absorption Spectroscopy (AAS). Data were statistically analyzed using the SPSS software version 17.0 for Windows. Correlation Matrix (CM), Principal Component Analyses (PCA) and Factor Analyses (FA) techniques were performed in order to identify the probable sources of HMs in the studied soils.
Results and Discussion: Comparing the measured HMs contents with their normal range in uncontaminated soils demonstrated the contamination of soils by Pb, Zn and Cd, with average concentrations of 152.8, 294.2 and 5.6 mg kg-1, respectively,whereas Ni and Cu did not show any pollution risk. The total concentration of Zn, Pb and Cd in the soil showed a great degree of variability, indicated by large coefficients of variation (CV) from 228.5 % of Cd to 354.8 % ofPb. These elevated CVs may indicate that these elements’ distribution in the studied area is influenced by an anthropogenic source. In contrast, the relatively low calculated CVs for Ni and Cu may imply that natural sources are responsible for these elements’ distribution in the studied soils. Correlation matrix (CM) analysis revealed high correlation coefficients between Zn-Cd and Ni-Cu, indicating the influence of the same factors in controlling their distribution. On the other hand, Pb contents showed low correlation with Ni and Cu values, whereas its correlation with Zn and Cd was relatively high. Therefore, it seems that Pb distribution in the studied soils is more influenced by the factor which controls the Zn and Cd distribution, rather than another factor that is responsible for accumulation of Ni and Cu in the studied soils. According to the PCA analysis, two significant components were extracted explaining about 84% of total variance. FA analysis showed that studied variables have a relatively high communality with two extracted principal components, indicating that almost all of the measured total variation can be efficiently explained by the extracted principals. Industrial activities in the Zinc Town seem to be the main factor which caused the high concentrations of Pb, Zn and Cd in the soil environment in this area; whereas Ni and Cu were associated with the natural sources including geology of the studied area (parental material’s factor). The obtained results from this study coincide with the prior studies indicating that multivariate statistics is a powerful technique for identification of probable sources of HMs in the soil.
Conclusions: The studied soils are classified as polluted soils with Zn, Pb and Cd,whereas Ni and Cu did not show any pollution risk. PCA and correlation analyses between HMs indicated that HM pollution in the studied area may originate from natural and anthropogenic factors. It can be concluded that Zinc Town controls the distribution of Zn, Pb and Cd in the surrounding soils, but Ni and Cu distribution in the studied area is mainly influenced by natural factors.Totally, industrial activities related to Zn production caused simultaneous entrance of several HMs to the adjacent soils and led to degradation of the lands in the studied area.