Soil Survey

views updated

Soil survey

A soil survey is a combination of field and laboratory activities intended to identify the basic physical and chemical properties of soils, establish the distribution of those soils at specific map scales, and interpret the information for a variety of uses.

There are two kinds of soil surveys, general purpose and specific use. General purpose surveys collect and display data on a wide range of soil properties which can be used to evaluate the suitability of the soil or area for a variety of purposes. Specific use soil surveys evaluate the suitability of the land for one specific use. Only physical and chemical data related to that particular use are collected, and map units are designed to convey that specific suitability.

A soil survey consists of three major activities: research, mapping, and interpretation. The research phase involves investigations that relate to the distribution and performance of soil; during the mapping phase, the land is actually walked and the soil distribution is noted on a map base which is reproducible. Interpretation involves the evaluation of the soil distribution and performance data to provide assessments of soil suitability for different kinds of land use .

During the research phase of the survey, soil scientists first establish which soil properties are important for that type of survey. They then establish field relationships between soil properties and landscape features and determine the types of soils to be mapped, preparing a map legend. In this phase, scientists also evaluate land productivity and recommend management practices as they relate to the mapping units proposed in the map legend.

Mapping is perhaps the most widely recognized phase of a soil survey. It is conducted by evaluating and delineating the soils in the field at a specified map intensity or scale. Soil profile observations are made at three levels of detail. Representative profiles are taken from soil pits, generally with laboratory corroboration of the observations made by soil scientists. Intermediate profiles are taken from soil pits, roadside excavations, pipelines or other chance exposures, and some sampling and description does occur at this level. Soil-type identifications are taken from auger holes or small pits, and only brief descriptions are made without laboratory confirmation.

With information gathered from sampling, as well as from the earlier research phase, soil scientists draw soil boundaries on an aerial photograph. These delineations or map units are systematically checked by field transects—straight-line traverses across the landscape with samples taken at specified intervals to confirm the map-unit composition.

Field research and the process of mapping produce a range of information that requires interpretation. Interpretations can include discussions of land use potential, management practices, avoidance of hazards, and economic evaluations of soil data. The interpretation of the information gained during a soil survey is based on crop yield estimates and soil response to specific management. Crop yields are estimated in the following ways: by comparison with data from experimental sites on identified soil types; by field experiments conducted within the survey area; from farm records, demonstration plots or other farm system studies; and by comparison of known crop requirements with the physical and chemical properties of soils. Soil response involves the evaluation of how the soils will respond to changes in use or management, such as irrigation , drainage , and land reclamation . Part of this evaluation includes an assessment of hazards that may result from changes such as erosion or salinization .

In general purpose surveys, which are the kind conducted in the United States, soils are mapped according to their properties on the hypothesis that soils which look and feel alike will behave the same, while those that do not will respond differently. A soil survey attempts to delineate areas that behave differently or will respond differently to some specified management, and the mapping units provide the basis for locating and predicting these differences.

[James L. Anderson ]