Effects of Finer Scale Soil Survey and Land-Use Classification on SWAT Hydrological Modelling Accuracy in Data-Poor Study Areas

The limited availability of high-quality spatial data often limits the development of hydrological modelling in developing countries. Hydrological models with data at different scales may generate large uncertainties in modelling outputs. This study analysed the accuracy of four SWAT built models that combine soil and land use/land cover (LULC) data at the scale of 1:250,000 and 1:100,000 in a basin of Mexico. SWAT model allowed determining that large-scale maps produced better results than data from small-scale. Sensitivity analysis with different soil data was less than LULC data. However, the small-scale can be used for exploratory purposes when testing SWAT performance.

A NATION-WIDE SOIL SURVEY RATIONALIZES EXPLOITATION OF VARIOUS SOIL RESOURCES

To tap the production potential of soil resources in China by making a nationwide soil investigation is a precondition for developing the farming production as a means of coping with the current population explosion and providing necessities for people’s livelihood.This article expounds practical methods for the survey and elucidates rational exploitation in line with soil conditions in different localities across the land.

Investigation and Evaluation of Site Contaminated Soil

The investigation and evaluation of site contaminated soil were mainly conducted.Firstly,investigation measures of site contaminated soil were proposed,including increasing attention to the production process of the original enterprise,investigating the types of pollutants on the site,clarifying the key points of different environmental investigations,and refining the initial record of site pollution investigation.Secondly,the key points of the risk assessment of site pollution were discussed.Finally,a specific case analysis was conducted,mainly covering the introduction of a contaminated site,investigation and evaluation methods,etc.,aiming to promote the smooth progress of the investigation and evaluation of site contaminated soil,and solve the problem of site pollution smoothly based on the in-depth perspective.

Employing Diversity and Similarity Indices to Evaluate Geopedological Soil Mapping in Miyaneh, East Azerbaijan Province, Iran

The geopedological viewpoint attempts to distinguish and introduce the smallest map unit that has the highest levels of homogeneity and uniformity with respect to landform, lithology, and soil, especially if the relationship between geomorphology and soils in the region is well defined. This research intended to investigate the degree of validity generalization of results obtained in the geopedology approach for similar landforms in the Miayneh region of East Azerbaijan Province, Iran. For this purpose, soil diversity study was conducted through measuring it in a hierarchical sequence in categories of USDA soil taxonomy and by comparing similar units in the geopedological method through employing pedodiversity and similarity indices. After preparing the initial interpretative map (based on aerial photographs) at a scale of 1:20,000, the HPu211 unit that covered the greatest delineation of study area was selected and 28 soil profiles, about 90 meters apart, were excavated, described, and sampled in this unit. The degree of validity generalization of geopedological results for the mentioned unit was determined by digging 14 other soil profiles in a similar unit, called the validation area, which was located outside of the sample area. Results indicated that the value of Shannon’s diversity index increased from the level of soil order to soil family in both the sample and the generalization areas;however, only at the soil family level were there significant differences between soil diversity in the two areas at the confidence level of 95%. As well as classification of the profiles dug in the generalization area was different from that of the profiles dug in the sample area at the category of soil family. Therefore, it is possible that management generalizability in this method, even at the detailed scale, can satisfy the related needs. Consequently, interpretative or managerial purity of geopedological units must be considered in future research.

Comparison and quantitative assessment of two regional soil erosion survey approaches

Regional soil erosion surveys are the first step of soil conservation planning.Grid and sampling ap-proaches are commonly used for soil erosion surveys at the regional scale.With the grid approach,the region is divided into grids(e.g.,1 km × 1 km),and the soil erosion rate of each grid was calculated.With the sampling approach,a small portion of the area(typically 4%or less)was taken and then the soil erosion rate was calculated.Based on the above calculation,both approaches evaluated the soil erosion area(which is the area where the soil erosion rate is greater than the soil loss tolerance(t))and its distribution in the whole region.The purpose of this paper is to compare the assessment results of the two approaches and analyse their practicality using Yunyang County,Chongqing,China(area is 3636 km^(2)).The soil erosion rate,percentage of soil erosion area(PSEA,which is the ratio of the area where the soil erosion rate is greater than the soil loss tolerance(t)to the area of the total study region)and its spatial distribution were compared between the two approaches.The results showed that the grid approach overestimated the average soil erosion rate and PSEA overall for all 33 sample units and the whole region in comparison to the sampling approach.The sampling approach can yield a reasonable spatial distribution of the soil erosion rate in the whole region.In addition,the soil erosion regions were more clustered than those using the grid approach,which can be more suitable for soil conservation planning.Therefore,the sampling approach is an efficient and practical approach in regional soil erosion surveys.The results can provide insights into regional soil erosion surveys.

Studies on Land Resource Inventory for Agricultural Land Use Planning in Northern Transition Zone of India through Remote Sensing and GIS Techniques

Land suitability analysis is a prerequisite to achieving optimum utilization of available land resources. Hence, a study on land resource inventory for agricultural land use planning was conducted in the Northern Transition Zone of India to determine land capability and develop a suitability map for wheat and sorghum-based on physical and climatic factors of production using remote sensing and GIS techniques. Detailed soil survey information was used for this exercise. Four series (Singhanhalli, Mugli, Bogur and Venkatapur series) were identified and mapped into seventeen mapping units. Land capability classification showed that a greater portion of the study area belonged to class III followed by class IV with limitations of erosion, wetness and varying soil properties. Four land capability classes viz., II, III, IV, and VI, and seven subclasses viz., IIsf, IIItsf, IVs, IVt, IVts, IVtsf and VIt were identified. Major limitations of these subclasses were slope, erosion, depth, texture, coarse fragments, pH, organic carbon and base saturation. Soil suitability assessment revealed that the soils are moderately suitable to permanently not suitable. About 234 ha (31.6%) is moderately suitable, 494 ha (65.0%) marginally suitable and 10.2 ha (1.3%) permanently not suitable for wheat;while 78.5 ha (10.3%) is moderately suitable, 633.4 ha (82.3%) marginally suitable and 32.6 ha (4.3%) permanently not suitable for sorghum respectively. The moderate, marginal and permanent non-suitability was due to moderate, severe and very severe limitations respectively. However, it is possible to achieve potential yield of the crops in the study area if these limitations are addressed.

The assessment of soil loss by water erosion in China

Soil erosion is a major environmental problem in China.Planning for soil erosion control requires accurate soil erosion rate and spatial distribution information.The aim of this article is to present the methods and results of the national soil erosion survey of China completed in 2011.A multi-stage,unequal probability,systematic area sampling method was employed.A total of 32,948 sample units,which were either 0.2-3 km2 small catchments or 1 km2 grids,were investigated on site.Soil erosion rates were calculated with the Chinese Soil Loss Equation in 10 m by 10 m grids for each sample unit,along with the area of soil loss exceeding the soil loss tolerance and the proportion of area in excess of soil loss tolerance relative to the total land area of the sample units.Maps were created by using a spatial interpolation method at national,river basin,and provincial scales.Results showed that the calculated average soil erosion rate was 5 t ha-1 yr-1 in China,and was 18.2 t ha-1 yr-1 for sloped,cultivated cropland.Intensive soil erosion occurred on cropland,overgrazing grassland,and sparsely forested land.The proportions of soil loss tolerance exceedance areas of sample units were interpolated through the country in 250 m grids.The national average ratio was 13.5%,which represents the area of land in China that requires the implementation of soil conservation practices.These survey results and the maps provide the basic information for national conservation planning and policymaking.

Assessment of SoilGrids data for soil erosion estimation at watershed scale: A case study in northern Thailand

Soil erosion has been identified as one of the most destructive forms of land degradation,posing a threat to the sustainability of global economic,social and environmental systems.This underscores the need for sustainable land management that takes erosion control and prevention into consideration.This requires the use of state-of-the-art erosion prediction models.The models often require extensive input of detailed spatial and temporal data,some of which are not readily available in many developing countries,particularly detailed soil data.The soil dataset Global Gridded Soil Information(SoilGrids)could potentially fill the data gap.Nevertheless,its value and accuracy for soil erosion modelling in the humid tropics is still unknown,necessitating the need to assess its value vis-à-vis field-based data.The major objective of this study was to conduct a comparative assessment of the value of SoilGrids and field-based soil data for estimating soil loss.Soil samples were collected from five physiographic positions(summit,shoulder,back slope,foot slope,and toe slope)using the soil catena approach.Samples were collected using a 5-cm steel sample ring(undisturbed)and a spade(disturbed).Data of the landform,predominant vegetation types,canopy cover,average plant height,land use,soil depth,shear strength,and soil color were recorded for each site.The soil samples were subjected to laboratory analysis for saturated hydraulic conductivity,bulk density,particle size distribution,and organic matter content.Pedotransfer functions were applied on the SoilGrids and field-based data to generate soil hydrological properties.The resultant field-based data were compared with the SoilGrids data for corresponding points/areas to determine the potential similarities of the two datasets.Both datasets were then used as inputs for soil erosion assessment using the revised Morgan-Morgan-Finney model.The results from both datasets were again compared to determine the degree of similarity.The results showed that with respect to point-based comparison,both datasets were significantly different.At the hillslope delineation level,the field-based data still consistently had a greater degree of variability,but the hillslope averages were not significantly different for both datasets.Similar results were recorded with the soil loss parameters generated from both datasets;point-based comparison showed that both datasets were significantly different,whereas the reverse was true for parcel/area-based comparison.SoilGrids data are certainly useful,especially where soil data are lacking;the utility of this dataset is,however,dependent on the scale of operation or the extent of detail required.When detailed,site-specific data are required,SoilGrids may not be a good alternative to soil survey data in the humid tropics.On the other hand,if the average soil properties of a region,area,or land parcel are required for the implementation of a particular project,plan,or program,SoilGrids data can be a very valuable alternative to soil survey data.

GIS approach for assessment of land suitability for different land use alternatives in semi arid environment in Jordan:Case study(Al Gadeer Alabyad-Mafraq)

The semi arid lands of Jordan are fragile and severely degraded due to low rainfall and mismanagement of natural resources.As human demands increase,sustaining the productivity of land becomes more and more important.Land suitability evaluation can contribute towards better land management;mitigation of land degradation;and designing land use pattern that prevents environmental problems through segregation of competing land uses.Suitability analysis allows identifying the main limiting factors for the agricultural production and enables decision makers to develop crop managements able to increase the land productivity.The purpose of this study was to develop a Geographic Information System(GIS)based approach for land use suitability assessment in order to assist land managers to identify areas with physical limitations for different land use alternatives based on research criteria developed by FAO and modified by stakeholders.This study was conducted using various data and maps incorporated within(GIS)in order to derive potential suitability for different Land Utilization Types(LUTs).Land suitability mapping was developed using an innovative approach that integrates soil and climatic data for land suitability assessment.Suitability maps for each land use were developed to show the suitability classes and display the spatial representation of soils suitable for agriculture.The output of suitability analyses provided not only the type of land use for which the land was suitable,but also information about the type of limitation(s)facing the utilization of the land.Optimum land use alternatives(scenarios)were formulated to improve and optimize the agricultural production in the study area.

Detection of Geochemical Element Assemblage Anomalies Using a Local Correlation Approach

As direct prospecting data,geochemical data play an important role in modelling prospect potential.Geochemical element assemblage anomalies are usually reflected by the correlation between elements.Correlation coefficients are computed from the values of two elements,which reflect only the correlation at a global level.Thus,the spatial details of the correlation structure are ignored.In fact,an element combination anomaly often exists in geological backgrounds,such as on a fault zone or within a lithological unit.This anomaly may cause some combination of anomalies that are submerged inside the overall area and thus cannot be effectively extracted.To address this problem,we propose a local correlation coefficient based on spatial neighbourhoods to reflect the global distribution of elements.In this method,the sampling area is first divided into a set of uniform grid cells.A moving window with a size of 3×3 is defined with an integer of 3 to represent the sampling unit.The local correlation in each unit is expressed by the Pearson correlation coefficient.The whole area is scanned by the moving window,which produces a correlation coefficient matrix,and the result is portrayed with a thermal diagram.The local correlation approach was tested on two selected geochemical soil survey sites in Xiao Mountain,Henan Province.The results show that the areas of high correlation are mainly distributed in the fault zone or the known mineral spots.Therefore,the local correlation method is effective in extracting geochemical element combination anomalies.