Soil structure

soil structure and its use in soil survey

1. Soil structure and its types

2. Zakir H ussain shigri Roll No : 105 Department of Soil and Environmental science University of Poonch Rawalakot

3. Soil structure The arrangement of soil particles and their aggregate into certain defined patterns is called soil structure. The primary soil particles i.e. sand ,silt and clay – usually grouped together in the form of aggregates. Natural aggregates called Ped. The cohesion with in these aggregates is greater than adhesion.

4. Structure is studied in the field under natural condition and it is describes under three categories . Type –shape or form and arrangement pattern of ped. Class – size of ped. Grade – degree of distinctness of ped. .

5. There are four principle form of structure. Plate-like: In this structural type aggregates are arranged in relatively thin horizontal plates. When the units are thick called platy and when thin, laminar . Prism-like : The vertical axis is more develop then horizontal. When the top of such ped is rounded called columnar and when flat called prismatic Type of structure

6. c) Block-like: All these dimensions are about the same size and the ped are cube-like with flat or rounded faces. When faces are flat and the edges sharp angular ,called angular blocky and when faces and edges are rounded ,called sub angular blocky . d) Spheroidal: (Sphere-like). All rounded aggregates are placed in this group. The aggregates of this group are usually termed as granular - relatively less porous. when the granules are very porous called crumby . -

7. Each primary structural type of soils is differentiated into 5- size classes depending upon the size of the individual peds. The terms commonly used for the size classes are: Very fine or very thin Fine or thin Medium Coarse or thick Very coarse or very thick. The term thin and thick used for platy and while the term fine and coarse for others. Classes of structure

8. Grade indicate the degree of distinctness of individual peds. It is determined by the stability of aggregates. It is influence by moisture content of soil . It also depend on O.M, texture etc. four term used to describe the grade of soil structure are. Structure less. There are no noticeable peds .e.g. loose sand. Weak structure. Indistinct formation of ped, which is not durable. Grade of structure

9. Compound structure : Smaller structural units may be held together to form larger units called compound structure. Naming of soil structure the sequence followed is grade, class and type. E.g. strong coarse angular blocky. moderate very coarse granular. . Moderate structure: moderately well developed peds ,which are fairly distinct. Strong structure : very well formed peds which are quite durable and distinct

10. Use of soil structure in soil survey

11. References. Fundamentals of soils by V.N SAHAI 1 st ed. 1990 Soil survey manual by USDA (Indian version) 2009