Soil mapping

• Soil Mapping is the process of delineating natural bodies of soils, classifying and grouping the delineated soils into map units, and capturing soil property information for interpreting and depicting soil spatial distribution on a map.

Soil mapping units 

                              Mapping unit may be defined as the classification of areas having similar soil components. It differ from other mapping unit in some of the soil characteristics dependinguponthe purpose, the following mapping units are being used in different kinds of soil survey. 

Soil series 

                        It is a mapping unit consisting of a group of soils having similar pedonprofilecharacteristics. Basically the morphological characters are taken into account for characterizingasoil series. The characters considered for characterization of a soil series are 

                      a. Arrangement of soil horizon 

                     b. Thickness of the individual horizon

                     c. Solum depth 

                     d. Soil colour

                     e. Soil structure 

                    f. Consistency

                    g. Presence of clay films

                    h. Soil pores 

                   i. Root distribution 

                   j. Development of surface cracks 

 By using profile characteristics we differentiate the soils in the field. The physical andchemical characteristics are not taken for mapping. The environmental characters likeslope, topography, stoniness, rockiness, soil erosion and the surface layers are not taken in toaccount for characterizing the soil. 

 Each soil series is named after the name of a village, town or famous temples in whichit isestablished. For establishing a soil series a minimum area of 2000 acres in required. Thesoil series is represented on the soil map by three letter symbol bearing the name of the soil series 

 eg:

         Plm - Pilamedu ,

        Tyr - Turaiyur,

        Igr - Irugur,

       Klt - Kalathur,

       Mdk - Madukkur,

       Tlk - Thulakkanur,

       Vgg - Vyalogam,

       Pvd - Palaviduthi, 

       Klk - Kallakudi,

       Plr - Puvalur,

       PKt - Pattukottai, 

      Omd - Omandur.

Soil Association 

     It is a mapping unit consisting of two or three soil series occur in a repeatedgeographical pattern. The boundaries of soil series can not be demarcated separately duetomap scale limitation. Under these circumstances mapping unit soil association proposed. 

eg: Palathurai - Pichanur soil series occur in association. This major soil series shouldbewritten first followed by the minor. Here also three letter symbol 

   Pth - Pch (Palathurai - Pichanur) 

  Plm - Pth - Pch (Pilamedu - Palathurai - Pichanur) 

Soil Complex 

     It is a mapping unit consisting of more than three series occurring together in a repeatedgeographical pattern. Boundaries can not be demarcated separately. It is a mapping unit inhillyterrains. It is indicated by Roman letters. The mapping units namely soil series, associationandsoil complex are used in the Reconnaissance soil survey. 

Soil type 

   It refers to the surface texture of soil series. It is denoted by the name of the soil seriesfollowed by the texture of the surface layer. eg: Plm - sandy loam 

Soil phase 

This is a mapping unit classified based on the environmental characters of the soil seriesnamely slope, erosion, stoniness etc. Type and phase mapping units are used in detailed soil survey .

Miscellanceous land types. 

    The areas which have little or no soil to support any vegetation are namedasmiscellaneous land types. These areas could be used only after proper reclamation. Mostlytheyare non soil however, they are indicated along with soil series, associations and complexes. Following are included in the above heading. 

i. Water bodies iv. Rubble lands ii. Salt pans v. Rockout crops iii. Sand dunes vi. Ravines …. etc. 

Inclusion 

      These are the soil not denoted in soil map. They are so small to be delineated. Normallysoils which occupy less than 20 per cent of the mapping area belongs to this type. 

Variants 

    These are soils of a established series differing in some properties of the series. Theyare indicated as variant of the series in reconnaissance soil series. These variants will beproposed as a new series during detailed soil survey. 

Mapping Symbol

    Maps use symbols to represent features on the ground. These features include roads, tracks, rivers, lakes, vegetation, fences, buildings, powerlines, administrative boundaries andthelike. Given the size of a map, it is not possible to show all features that occur on the ground. Largescale maps show more details and a larger number of features. Colour plays an important part insymbols for example, blue for water features and green for vegetation. 

 Map scale 

   A map represents a given area on the ground. A map scale refers to the relationship(or ratio) between distance on a map and the corresponding distance on the ground. Map scales canbeshown using a scale bar. 

Based on the scale of mapping, the map is called as 

Large scale maps - 1: 5000 and less

Medium scale maps - 1:25,000 to 1:40,000 

Small scale maps - 1:50,000 to 1: 2, 50,000

Very small maps - 1: million and above 

Larger the scale of a map, smaller the area that is covered and more detailed is the graphic representation of the ground. Small scale maps (such as 1:250 000) are good for long distance vehicle navigation, while large scale maps (1:50 000) are ideal for travel on foot. Scales are usually shown in increments of one, five or 10 kilometres. Soil maps generallycontain more than one map unit. These units are arranged in many ways. An organizedlist of map units is called a Legend. There are several kinds of legends. Map units have symbols, colours and names. The nomenclature may differ from one legend to another. 

Taxonomic units Versus Mapping units

  Taxonomic units define specific range of soil properties in relationship to the total range of properties measured in the soil. The map units and their individual delineations defineareason a landscape. Every mapping unit has more than one taxonomic unit (soil series or soil phase).

 Kind of mapping units

  Mapping units have been distinguished based on the amount of inclusion or impurity they contain. Five kind of mapping units have thus been distinguished and these are consociation, association, complex, undifferentiated and miscellaneous/unvisited. 

Consociation

  A consociation is a mapping unit with very little inclusion or impurity. It is assumedtocontain the profile class after which it is named but in practice the purity of such class mayrangefrom 70% to 85%. 

Association

An association is a mapping unit that contain two or more taxonomic class that are nearly equally represented and in which it is very easy to separate one profile class from the other.

 Complex

  Complex is a mapping unit where more than two taxonomic classes are equally represented and the components are intricate so that separation, even at large scale is difficult. 

Undifferentiated 

This is a mapping unit consisting of a number of taxonomic units that are merged so that separation into different units are impossible at any reasonable mapping scale