Types of soil survey

Types of soil survey

Depending upon the objective, method, type of base map available and intensity of observations following types of soil surveys are recognized. They are,

1.Reconnaissance

2.Detailed

3.Detailed - reconnaissance

4.Semi- detailed

5.Exploratory

6.Rapid reconnaissance

Reconnaissance

         The reconnaissance survey is undertaken to prepare resource inventory of large areas. It identifies broadly, the kinds of soils and their extent of distribution. It enables to asses broad potentialities of soils and recognition of areas of promise that are suitable for intensive agriculture and that requiring priority treatment for amelioration. It is low intensity soil survey.

The survey relies on aerial photo or remotely - sensed data interpretation to develop soil physiographic relationship. The soil map provides information needed for broad or regional level planning in respect of land use. This kind of mapping proceeds detailed soil survey of potential areas.

Scale of mapping              : 1:250000 to 1:100000 / 1:50000

Base map                           :  Toposheets, aerial photographs or satellite imageries

Intensity of Observation : Soil profile is examined at 3-6 kms or even shorter, depending upon soil heterogenity. Auger sampling is done at an interval of 2.5 to 1 km.

Mapping units                   : Association of soil series, families and great groups

Purpose of RSS                : It provides information needed for broad land use planning and agricultural development. The information obtained is used for Taluk, district and state level planning.It precedes detailed soil survey and mapping.

Target : 1000 acres / day / soil survey party (SSP)

Traversing for RSS         

Steps involved in RSS

Pre-field study using base map

         The toposheets for the particular area to be surveyed to be obtained and information regarding geology, land use of area and other particulars are gathered. This gives some information before field visit.

Rapid traversing of the area  (by jeep)

         Soil survey party (SSP) takes up rapid travel in all the main road to study the distribution of different kinds of soil. During the travel, soils will be examined at larger intervals. The heterogeneity of the soils and distribution are known during this stage. SSP will be in a position to know tentatively the number of soil series distributed in a study area.

Fixation of soil legends

         Five to ten profiles will be opened for each group of soil identified in step – viz., red soil, black soil. The profile characteristics will be examined and range of characteristics for each group will be fixed.

Legend of RSS comprises of

• Location of the study area

• Physiography

• Geology

• Tentative soils series

• Profile morphology of the tentative soil series

A graph comprising the climate, geology, land use and kinds of soil with range of characters will be prepared and circulated among SSP for use. This forms the legend which is amenable for modification if any during the course of regular field work.

Regular field work

SSP divide among themselves and initiate the field work from different points of the study area. They delineate / indicate the boundaries of soil identified in the legend. The mapping of the boundaries is done by examining the profile are 4 to 6 km intervals an auger sampling at an interval of 1-2 kms. If a SSP comes across a new kind of soil during the field work other than hat was fixed in the legend, then a new name will be proposed and the boundaries will be delineated by profile examination.

The mapping units used for delineation include soil series, soil association, soil complex. Areas which are accessible will be examined and the boundaries will be extended to the inaccessible areas. This process is known as Extrapolation.

Collection of soil samples

After completion of field work, soil samples are collected from the representative profile for each soil series for analysis. Monolith soil series may be collected from representative profile which may be used for soil correlation studies. In RSS, subsoil characters are given prime importance.

Detailed

This type of survey is undertaken in priority areas, such as pilot projects, agricultural research stations, micro water sheds and areas in urban development. The traverse lines are on grid pattern. The survey enables identification of soil units up to phases of series for planning development of individual parcels of land. The resulting soil map provides sufficient information for interpretation of various kinds of soils and for understanding their pedogenic evolution. Such a survey is very time consuming and expensive. The detailed soil survey is of two types ie low and high intensity.

It is a high intensity soil survey.

Scale of mapping              : 8” =  1 mile; 16” = 1 mile

Base map                           : Cadastral map / village map

Intensity of Observation  : Soil profile is examined at every one ha and auger                                                         sampling at an interval of 0.25 to 0.5 km.

Mapping units                   : Soil type, soil phase

Purpose of RSS                : It provides information needed for village, farm and block level planning.

Target                                  : 200 acres / day / soil survey party (SSP) – 40,000 acres per year

Steps involved in DSS

1.  Conduct RSS

2.  Initial traverse of the study area – A rapid traverse will be taken up to know the distribution of soil types and soil phases of soil series by SSP. The list of types and phases of the soil series is prepared and used as a guide during the regular field work.

3.  Legend – The soil legend gives a range of soil texture in the soil series, depth range, slope and erosion classes.

4.  Regular field work – SSP will start the work from a permanent point. Mapping units such as phases and types of soil survey will be demarcated during traverse. SSP cover the study area in foot while RSS in jeep. SSP walks in a zig-zag manner. During the traverse party will examine the soil series at an interval of 0.25 to 0.5 km by auger boring and every 640 acres by profile digging. Difference between two traverse lines will be minimum of 0.25 km. Thus boundaries of the types and phases are demarcated. After completing he DSS, soil samples are collected from the representative soil profile from each mapping unit prescribed for DSS.

5.  Mapping units for a DSS

The mapping units for a DSS are written like a formula. It consists of name of the series, surface texture, depth class, slope and erosion class.

E.g. pth-sl-d5 -B-e2

Where,

pth - Name of the soil series

sl - surface texture of the soil series

d5 - Depth of solum

B - Slope percentage

e2 - Erosion class

pth-sl-d5 - Soil type

B-e2 - Soil phase

Those areas which could not be delineated separately because of their smaller extent can be denoted by conventional symbols.

Conventional symbols

         Rock out crops                              

         Moderate wind erosion

         Severe wind erosion

         Moderate sheet erosion                  S

         Severe sheet erosion                      SS

         Moderate gully erosion                   G

         Severe gully erosion                       GG

         Saline spot                                      +

Alkaline area

         Slightly affected                                         

         Moderately affected                      

         Severely affected

         Gully

         Slope direction                                                       

Detailed - Reconnaissance

         This kind of survey combines both the detailed and reconnaissance surveys as above and is undertaken for understanding distribution of basic soil classes of series / families and their phases.       First RSS is conducted for the whole study area and this is followed by DSS in selected areas such as intensively cultivated areas, problem soil areas, wasteland development, polluted soil areas or potential areas for a particular crop variety.

Ex. If the problem soils of Coimbatore is to be studied, RSS is to be undertaken for the whole area and DSS in those problematic areas identified.

Semi-detailed

         This survey comprises very detailed study of some selected strips cutting across many physiographic units for developing correlation between physiographic units and soils. Once correlation is developed and is found to be valid by random checking, the rest of the area is checked at random and soil boundaries based on physiographic units delineated. This kind of survey provides sufficient information about various kinds of soils including problematic or degraded soils. Scale of base maps (aerial photographs or satellite imagery) used is 1:50,000. Mapping unit is the association of soil series or families. The final maps are prepared on 1:50,000 scale.

Exploratory

Exploratory surveys are not survey proper. They are usually rapid road traverse made to provide modicum of information about the area that are otherwise unknown. Scale of exploratory survey varies from 1: 2,000,000 to 1,500,000. These lead to preparation of small scale soil maps that are needed for macro level planning for varied agro -based development programmes.

Rapid reconnaissance

In this survey, field mapping is done at 1:1000000 or still smaller scale using the satellite imagery. Soils are mapped by traversing representative areas. The mapping units are phases of great groups. Observations are done at an interval of 1-2.5 km.

Soil and Landscape characteristics observed during soil survey

I site features

         The following site features are to be observed during the examination of soils.

i. Location and geographical landscape

         Location of the profile should be indicated with reference to latitude and longitude. It should be away from roads, buildings and should represent the area. The geographical land features like basin, depression,etc. are to be indicated. Elevation also indicated.

ii. Slope

         The percentage of slope and direction of the slope are to be indicated. Appropriate symbols should be used to indicate slope nature according to standard classes recognized.

iii. Climate

         The various climate data like rainfall, temperature, potential evapotraspiration, and soil moisture and soil temperature are to be recorded. Here more emphasis is given for the temperature regions.

iv. Vegetation

         It refers to the natural vegetation. Here land use also considered. Based on the land use it is described as forest, crop land, terraced land, pasture land, plantations etc.

v. Erosion

         It refers to removal of soil material by wind and / or water. Gradations of wind erosion viz slight, moderate, and severe and water erosion viz., splash, rill, sheet, gully etc are indicated.

vi. Ground water

         It refers to depth from soil surface to the body of water surface. This information is being collected by enquiring the local people and also by observing the open well in that area.

vii. Parent material

         The base material from which soil is formed is to be noted. The type of rocks viz., igneous, sedimentary, metamorphic etc is also indicated.

viii. Drainage

         The various drainage classes viz., partial, imperfect, moderate, well and excessive are noted by appropriate symbols.

ix. Presence of stones and rock out crops

         The material having the dimension ranging from 75-250 mm is called stones. The classes of stoniness are very few, fairly story, stony, very stony, excessively stony and Ribbed land, which are based on percentage of area covered by stores.

x. Presence of salt / Alkali

         It refers to the accumulation of salts usually linked with white alkali. This is recorded by observing the white patches on the surface of the soil. This will be confirmed by laboratory analysis and grouped into classes.

xi. Moisture content of the soil

         The prevailing moisture content of the profile is to be recorded

xii. Higher category level of soil

         The higher category levels of soils like order, sub order and great group etc are recorded.

II. Profile features :

         The soil profile must be perpendicular to sun’s movement for observation and taking photograph.  It should be always North-South.  The length at North-South should be 2 meter and width at East-West should be 1.5 m.  Depth of profile should be 2 m or up to parent rock or up to water table which ever is less.  While digging profile pit the surface, sub surface soil must be kept both North and South sides In profile, the steps are provided in North – South direction, for easy and close observation.  The profile pit is examined at morning on western side and at evening on eastern side . Following parameters are studied in a profile for better understanding and classification of soils.

(i)  Horizon symbol:

      In a profile first  boundaries of different horizons are to be marked by observing colour difference. On marking boundaries, they (horizons) have to be named using symbols as per latest nomenclature.

(ii) Horizon thickness:

       Each horizon thickness is to be recorded. This will indicate the development nature of the soil in that area.

(iii) Colour:

        The colour of each horizon is recorded using Munsell colour chart both in wet and dry conditions.

(iv) Mottlings:

         Spots / streaks of different colours ( usually orange or grey) inter spread with the dominant  soil matrix colour developed due to periodic reduction/ water-logged and oxidation conditions. Mottling with chroma 2 or less indicate poor drainage. Mottlings described in terms of three characteristics viz. abundance, size, contrast etc.

(v) Texture:

      The texture of each horizon is recorded initially by feel method and later confirmed by laboratory analysis.

(vi) Structure:

       The arrangement of soil particles in each horizon is indicated by using appropriate symbols.

 (vii) Consistency:

             It is the behavior of soil cohesion under various moisture condition towards any force. The consistency of soil is observed and symbol of appropriate classes is indicated.

(viii) Cutans / clay films:

            These are thin oriented clay on surfaces or in soil pores. During the field investigation it can be observed as thin shiny surfaces either on pits or in pores by using 10x or 20x hand lens. Based on thickness it is classified as thick or thin. Based on the abundance it is classified as patchy or continuous.

(ix) Concretions:

        These are hardened materials found in soil horizons. They are formed due to secondary accumulation of soil materials around a nucleus. These are described using characteristics like abundance, size and types.

(x) Soil pores:

      The soil pores in each horizon is indicated by characteristics like abundance and size.

(xi) Presence of roots:

       This is described in terms of abundance and size.

(xii) PH of soil horizons:

        The PH of each soil horizon is recorded using PH indicator papers at field. Later it is confirmed with laboratory analysis.

(xiii) Carbonates:

         1:10 HCl applied on each horizon individually. The effervescence indicate the presence of carbonates. Based on degree of effervescence classes are identified and noted.

III Analytical data:

i) Mechanical Analysis              - International pipette method.

ii) Moisture content                   - Oven dry basis

iii) PH                                           - By PH meter

iv) Electrical conductivity             - By EC meter

v) Organic carbon content          - By Walkley and Black method.

vi) Total Nitrogen content           - By Kjeldahl’s method.

vii) CaCO3  content                   - By rapid titration method.

viii) Cation Exchange capacity   - Ammonium acetate method for soils 

Ix) Individual cations                   - Ca and Mg – EDTA method

   (exchangeable)                          Na and K – Flame Photometer method

x) Base saturation percentage  -   Total cations – H / CEC x 100

xi) Exchangeable Na percentage -  Exchangeable Na / CEC x 100

(ESP)

xii) Sodium adsorption ratio           - Na / Ca+ mg / 2

xiii) Available water                 -  By using pressure plate apparatus

xiv) Micro nutrients                 - By Atomic Absorption Spectrophotometer

Relationship of scale of soil map and frequency of field observations

Kind of survey    Scale of map Area represented by 1cm2 on map (ha) Distance between field observations

Frequency of observation

Mapping unit

Field procedure and accuracy of soil boundaries

Rapid Reconnaissance / extensive (for selection of area for more intensive study)

1 : 1000000 or smaller

10,000

10 km

1 in 10,000 ha

Phases of soil great groups

Soil identification is done by traversing representative areas to determine soil pattern and composition of map units. Boundaries are plotted by interpretation of remotely sensed data. Reconnaissance / (for regional planning)

1 : 2,50,000       1 : 1,00,000 

625

100

2.5 km

1.0 km

1 in 625 ha

1 in 100 ha

Phases or association of soil series, families / great groups

Soil identification is done by traversing sample strips, boundaries plotted by interpretation of remotely sensed data and verified by random observations.

Semi - detailed / (for district planning)

1 : 50,000      

25

500 m

1 in 25 ha

Phases of soil series or association of soil series, families

Boundaries in each delineation of sample areas are identified by actual traversing

Detailed (for village / watershed planning)

Low intensity

1:10,000

1

100 m

1 per ha

Phases of soil series

Almost all boundaries are checked by actual traversing; remote sensing data are used as an aid in boundary delineation

High intensity

1:5,000

0.25

50 m

4 per ha

Phases of soil series

All boundaries are checked by actual traversing