| Soil survey |
Soil survey: The survey which includes the systematic examination, description, classification & mapping of soils of a particular area, is called soil survey.
Soil survey reports includes…………………………………………
· Soil classification along with the base map & soil profile characteristics.
· Description of soil, topography, climate.
· Suggestions for agricultural & non agricultural uses.
· Soil survey report is prepared on the basis of soil characteristics.
· Soil classification is done based on soil profile characteristics & classified soils are located on base map & the mature soils as they occur in the field are described.
Base materials used in soil survey……………………………………………….
For conducting soil survey following kinds of base material are used—
· Topographic map: to show hills, valleys, roads, buildings, agricultural fields, boundaries & other relevant features which help to find out the area to be surveyed.
· Aerial photograph: to show topographic details & very suitable for conducting soil survey in forests covering a vast area.
· Aerial mosaic: prepared by combining several conductive aerial photograph together to cover a large area in one photograph.
· LANDSET or satellite imagery: the common application in forest survey. It is best suited to the initial reconnaissance of very large area.
Soil series………………………………………..
· A group of soils developed from a similar parent material & that have similar profile characteristics, except the surface texture of the soil known as soil series.
· In a series, soils are homogenous in slope, stoniness, degree of erosion, topographic condition & depth to bedrock.
· Soil series is the lowest category in soil taxonomy & one soil series is different from another in a family by one or more but not all soil properties.
Basis of a soil series………………………………………….
· Soil series are established based on soil profile characteristics.
· This requires careful study of various horizons for thickness, texture, structure, color, organic matter, pH etc.
· In series identification sub surface soil texture is taken into consideration, because surface soil may be washed away through erosion or may be deposited one.
Soil phases…………………………………………………..
· Soil phases is the subdivision of soil series, because of the differences in degree of slope, erosion, salinity, flooding etc, content of stone, manmade features & similar other reasons.
· It is technically not a category in soil taxonomy but used in field surveying.
Types of soil survey……………………………..three types
1. Reconnaissance soil survey:
· The smallest scale of survey to achieve coverage of the whole area & much use is made of aerial photographs interpretations.
· Some smaller country are completely covered by reconnaissance soil survey, e.g Srilanka, Uganda.
2. Semi-detailed soil survey:
· Survey is done by aerial photograph interpretations combined with a substantial amount of field survey.
· Mapping units vary from soil land from classes to soil associations & series, e.g Western Samoa, Peninsula, and North Borneo.
3. Detailed soil survey:
· They are produced mainly by field survey.
· The usual mapping units are soil series & phases of series, e.g. Kongwa, St. Vincent.
Procedure of soil survey in a forest area…………………………………………………………………….
1) Before commencing fieldwork, a legend containing brief description of diagnostic characteristics of probable soil series to be studied & relief position they occupy is prepared.
2) Transverse lines are planned on changed photos across the configuration pattern at an interval of about 100m.
3) Auger, color chart, pH kit etc, instruments are used for soil survey.
4) Soils are cheeked up to 1m depths through traverse line at every 100m for soil thickness, color, texture, pH etc, of the sub surface soil.
5) Information thus obtained recorded on enlarged aerial photograph (1: 5000). Boundaries between soil mapping units are delineated on aerial photographs.
6) Soil associations are generally shown as mapping units instead scale series, because of its intricate nature.
7) Soil is collected from each horizon of a profile dug out for each series.
8) Soil samples are brought to the laboratory where the physical & chemical analyses of the collected soils are done.
9) Finally a report is prepared based on information collected from field & analytical data of the soil in the laboratory. The report is accompanied by several maps showing soil associations with other related information.
Modern technologies for soil survey…………………………………………….
a) By Video Images Analysis (VIA):
· Aerial photograph are examined to distinguish up to 256 shades of gray.
· This color differences are related to soil & vegetation variations.
· Using appropriate computer techniques, soil differences can be more clearly delineated.
b) Ground Penetrating Radar (GPR):
· Used to increase the quality & reduce the cost of survey.
· High frequency impulses of energy are transmitted into the soil.
· Energy is reflected back to the surface when the impulses strike an interface between soil particles.
· This reflectable energy is measured & displayed on a recorder.
· This technique is not applicable for all soils & its cost is only one third of the conventional soil survey.
The uses of soil survey…………………………………………………………………………….
· Scientists used them to facilitate research on crop production, land cultivation, zoning & human settlements.
· Extension specialists & agriculturists make recommendations for land use & crop management based on reports done by soil survey.
· Using soil survey maps & reports engineers & hydrologists can select superior roadbeds & buildings sites & also can estimate of water runoff & infiltration.
· Homeowners can use the reports as a basis for selecting trees & shrubs for landscaping.
· Soil survey maps & reports are the two bases for land capability classification.
· Soil survey can also be used to determine land suitability for agriculture & other purposes.
· Soil survey is of greatest practical value in land classification for agricultural & other uses.
· In Bangladesh agro ecological & dendroecological regions are described & mapped based on soil information described in various reports published for district & upazilla levels.
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| Prepared by Rasel 23 |
