After reading this article you will learn about the definition, purpose and types of soil survey.
Definition and Purpose of Soil Survey:
A soil survey is the systematic description of soils in the field, their grouping into well-defined mapping units like soil series, phases etc. to identify their best use and show their location on the map.
The purpose of soil survey is discussed below:
1. To classify soils into well-defined mapping units i.e. soil series, phases etc.
2. To shows their distribution in the field on the map.
3. To find out their best use.
4. To predict their performance under different management practices i.e. yields of crops under different management practices.
Types of Soil Surveys:
Soil surveys are of three types:
(i) Detail Soil Survey:
Soils are studies in detail. Soil boundaries are demarcated on a large scale (1:10,000 to 1:5,000) base map called cadastral map. Mapping units is soil series.
Method of Detail Soil Survey:
Soils are grouped into units possessing certain common physical properties and also morphological properties, which can be readily recognized in the field.
Physical and morphological properties are texture, structure, colour, pH, carbonate, natural vegetation, slope, erosion, depth of soil, natural vegetation etc.
The soil units are usually defined on the basis of the above-mentioned characteristics of the surface soil, soil depth, slope and erosion and the soil profile. The soil units are the soil series. Cadastral (village) maps are the base maps (Scale 1: 10,000 to 1: 5,000).
Select a convenient starting point like a bench mark, or building or pond, or anything in the field and identify the same on the cadastral map (1: 10,000 to 1:5000).
The Soil Surveyor moves up or down the slope because usually the soil properties change in that direction.
Start walking down the slope from the starting point i.e. the bench mark in the Fig. 7.1 and continue observing the natural vegetation, slope of the land/soil erosion, soil depth, soil colour, texture, by feeling the Soil; pH with the help of universal indicator; and carbonate with the help of dilute acid at an interval of about 100 to 200 metres.
As you are walking down the slope and studying these properties, you suddenly find that a number of soil characteristics change; For example, slope erosion, soil depth, colour, texture etc. Then, follow the line of change in the soil properties as shown in Fig. 7.1 and demarcate it. This is the boundary between the soil units A and B.
Resume walking down (Traversing) the slope till you again find that number of soil characteristics change. Follow the line of change of soil properties between the soil units B and C and demarcate it on the field. In a similar way, find out and demarcate the boundaries between soil units C and D, D, and E and so on as shown in Fig. 7.1.
Then dig profiles in each of the soil units A, B, C, D and E the number of profiles depend on the relative area of the soil units.
Study profiles, the characteristics of which become the basis of identifying soil series. If the characteristics of the profile in soil units A, B, C, D and Eare different then the soul units A, B, C, D and E become the soil series A, B, C, D and E. Then a soil survey report is written, describing the soil series and providing other useful information about the area.
(ii) Reconnaissance Soil Survey:
Soils are not studied in detail i.e. observations are taken at a longer interval and noted down on the Survey of India toposheets of scale 1: 2,50,000 to 1: 50,000. The mapping unit is soil association.
(iii) Detailed Reconnaissance:
First reconnaissance soil survey is carried out and subsequently about 15 per cent of the area where research projects are to be established, are surveyed in detail.