Methods of Soil Surveys

 

Introduction

Soil survey is a complex process of mapping a parcel of landscape. Soil survey is necessary because of variability or changes experienced in soils from time to time. Such changes may be gradual in vertical or horizontal directions. Changes in a particular soil property may not necessarily imply changes in another thereby resulting in an identical combination in a particular landscape. However, there are methods involved is soil survey activities. These methods include pre-field, field and post-field activities. Pre-field Preparations: These include, collation and study of existing data of the area i.e. maps, reports, top o-sheets and analytical data, general field reconnaissance, aerial photo assemblage and interpretation, and design and planning of field survey. Field Survey: Activities include, soil mapping operation and land evaluation operation. The soil mapping operation involves identification and classification of the soil types present in the area, and surveying their distribution, leading to the production of a soil map. The land evaluation operation includes field activities for assessing the potentials of the various soils for a range of alternative types of land use, and the identification of possible development hazards.

 Important facts to know

·       Pre-field Preparations include, collation and study of existing data of the area i.e. maps, reports,top o-sheets and analytical data, general field reconnaissance, aerial photo assemblage and interpretation, and design and planning of field survey.

·            Field Survey activities include soil mapping operation and land evaluation operation. The soil mapping operation involves identification and classification of the soil types present in the area, and surveying their distribution, leading to the production of a soil map.

·            Post Field Operations: Aerial photo interpretation is revised in the light of field observations. The soil samples collected are analyzed. The data are also analyzed.

 Methods of Soil Survey

Pre-field Preparations: Pre-field Preparations include, collation and study of existing data of the area i.e. maps, reports, top o-sheets and analytical data, general field reconnaissance, aerial photo assemblage and interpretation, and design and planning of field survey.

Field Operations: There are two methods of field survey namely; Free survey and Grid survey

1. Free Survey: In the Free Survey, the surveyor uses his judgment of the objectives of the survey and all the available aerial photos and ground evidence to locate profile pits of the most useful and representative sites. The number of the profile pits depends on the requirements of the survey and the complexity of the soil pattern. The free survey is only feasible in “open” areas, in grass or arable regions. The surveyor uses a lot of observable field marks and taking auger borings in relation to every change of vegetation or edaphic features. Aerial photo interpretation will be of immense help in this method.

2. Grid Survey: Here, observations are made at regular intervals along pre-determined traverses in the survey area. This method is especially useful for large scale high intensity detailed surveys and intensive surveys. However, there is no alternative to grid survey for areas under forest or broken topography where accessibility is difficult and areas where adequate aerial photos or top o-sheets are not available. It is generally employed in dense forests and swamps where photo interpretation is often of limited usefulness and there is no way of finding one’s position except by measurement. A ‘rigid grid’ pattern of cut traverses is essential with a central baseline, between regularly spaced straight traverses. The grid survey is very tedious, expensive, and time consuming because it takes a lot of time cutting traverses through the forest, chiseling or augering at regular intervals.

 Advantages of grid system include

a)         Traverses provide access between roads in the dense forests

b)         Sampling points along the traverses can be located and mapped with accuracy

c)          The direction of the traverses can be arranged to cross the topographical ‘grain’ of the country,

d)         The greater part of the field survey can be carried out by soil survey assistants with minimum supervision by the surveyor

e)         The traverse grid provides a uniform sampling point within which it is very unlikely that important soil types will be overlooked.

Field Observations: Field observations include the following; soil profile observations, which include description of the environment, general information on the soils and brief and detailed profile descriptions. Others include brief descriptions and classification of chisel holes, site descriptions –including vegetation / land-use, slope measurement, drainage and geology. Also, detailed descriptions of modal soil profiles and sampling for laboratory analysis must be carried out. Soil mapping operations involve identification and classification of the soil types, their distribution and production of a soil map.

Post Field Operations: Aerial photo interpretation is revised in the light of field observations. The soil samples collected are analyzed. The data are analyzed. The survey report is written. The unit of mapping is usually the soil series.

 CONCLUSION

Soil Survey methods include pre-field, field and post-field activities. Pre-field Preparations: These include, collation and study of existing data of the area i.e. maps, reports, topo-sheets and analytical data, general field reconnaissance, aerial photo assemblage and interpretation, and design and planning of field survey. Field Survey: Activities include soil mapping operation and land evaluation operation. The soil mapping operation involves identification and classification of the soil types present in the area, and surveying their distribution, leading to the production of a soil map.

Pre-field Preparations include, collation and study of existing data of the area i.e. maps, reports, top o-sheets and analytical data, general field reconnaissance, aerial photo assemblage and interpretation, and design and planning of field survey. Field Survey activities include soil mapping operation and land evaluation operation. The soil mapping operation involves identification and classification of the soil types present in the area, and surveying their distribution, leading to the production of a soil map. Post Field Operations: Aerial photo interpretation is revised in the light of field observations. The soil samples collected are analyzed. The data are also analyzed.

Also read on: << Definition and Description of Soil Survey>>

                 <<The Principles and Purpose of Soil Survey>>