Soil Mapping Units

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1. Soil Mapping Units Lecture 3

2. 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 depending upon the purpose, the following mapping units are being used in different kinds of soil survey. 2 5/3/2023 Add a footer

3. A soil map delineates the areas occupied different kinds of soils Each has unique set of inter- related properties, materials its environment and history. A map unit is a collection of soil components or miscellaneous areas or both Each map units differs in some respect from all others in a survey area and is uniquely identified on a soil map. Map units consists of one or more components 3 5/3/2023 Add a footer

4. An individual component of a map unit represents the collection of polypedons or parts of polypedons that are members of the taxon or a kind of miscellaneous area (inclusion) Soil boundaries are shown on maps by lines. Area enclosed by a boundary is called a soil delineation Several map units on a map unit symbols, colors and names is called as map legend 4 5/3/2023 Add a footer

5. Soil series A soil series is a taxonomic unit represents a group of soils having horizons similar in characteristics and arrangement in a soil profile developed from a particular type of parent material but they may differ in the surface texture. It is given a geographical name either of locality where it is well developed or where it was recognized first. For establishing a soil series we should require a minimum area of 2000 acres. 5 5/3/2023 Add a footer

6. Example 6 5/3/2023 Add a footer Plm - Pilamedu Tyr - Turaiyur , PKt - Pattukottai Omd - Omandur Igr - Irugur Klt - Kalathur Klk - Kallakudi Plr - Puvalur Mdk - Madukkur Tlk – Thulakkanur Vgg - Vyalogam Pvd - Palaviduth

7. The characters considered for characterization of a soil series are Kind and arrangement of soil horizon Texture Thickness of individual horizon Consistency Solum depth Concretions Soil color Soil structure Mottling's Soil pores Presence of clay films/ Slickensides Development of surface cracks Root distribution 7 5/3/2023 Add a footer

8. By using profile characteristics we differentiate the soils in the field. The physical and chemical characteristics are not taken for mapping. The environmental characters like slope, topography, stoniness, rockiness, soil erosion and the surface layers are taken in to account for characterizing the soil. 8 5/3/2023 Add a footer

9. Soil type and Soil phase Soil type It refers to the surface texture of soil series. It is denoted by the name of the soil series followed 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 series namely slope, erosion, stoniness etc. Type and phase mapping units are used in detailed soil survey. 9 5/3/2023 Add a footer

10. Inclusion and Variants Inclusion These are the soil not denoted in soil map. They are so small to be delineated. Normally soils which occupy less than 20 per cent of the mapping area belongs to this type. Variants or polypedons These are soils of a established series differing in some properties of the series. They are indicated as variant of the series in reconnaissance soil series. These variants will be proposed as a new series during detailed soil survey. 10 5/3/2023 Add a footer

11. Mapping Symbol Maps use symbols to represent features on the ground. These features include roads, tracks, rivers, lakes, vegetation, fences, buildings, powerlines, administrative boundaries and the like. Given the size of a map, it is not possible to show all features that occur on the ground. Large scale maps show more details and a larger number of features. Colour plays an important part in symbols for example, blue for water features and green for vegetation. 11 5/3/2023 Add a footer

12. 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 can be shown 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 12 5/3/2023 Add a footer

13. 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 define areas on a landscape. Every mapping unit has more than one taxonomic unit (soil series or soil phase). 13 5/3/2023 Add a footer

14. 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 Miscellaneous/unvisited . 14 5/3/2023 Add a footer

15. Consociation A consociation is a mapping unit with very little inclusion or impurity. It is assumed to contain the profile class after which it is named but in practice the purity of such class may range from 70% to 85%. 15 5/3/2023 Add a footer

16. Association It is a mapping unit consisting of two or three soil series occur in a repeated geographical pattern. The boundaries of soil series can not be demarcated separately due to map scale limitation. eg : Palathurai - Pichanur soil series occur in association. This major soil series should be written first followed by the minor. Here also three letter symbol is used. Pth - Pch ( Palathurai - Pichanur ) Plm - Pth - Pch ( Pilamedu - Palathurai - Pichanur ) 16 5/3/2023 Add a footer

17. Soil Complex It is a mapping unit consisting of more than three series occurring together in a repeated geographical pattern. Boundaries can not be demarcated separately. It is a mapping unit in hilly terrains. It is indicated by Roman letters. The mapping units namely soil series, association and soil complex are used in the Reconnaissance soil survey. 17 5/3/2023 Add a footer

18. 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 18 5/3/2023 Add a footer

19. Miscellanceous land types The areas which have little or no soil to support any vegetation are named as miscellaneous land types. These areas could be used only after proper reclamation. Mostly they are non soil however, they are indicated along with soil series, associations and complexes. i . Water bodies iv. Rubble lands ii. Salt pans v. Rock out crops iii. Sand dunes vi. Ravines …. etc. 19 5/3/2023 Add a footer