SOIL CLASSIFICATION

AGRICULTURE RESEARACH AGRICULTURE RESEARACH INSTITITUTE (ARI)TANDOJAMINSTITITUTE (ARI)TANDOJAM

MASHOOQ HUSSAIN ODHANO ASSISTANT RESEARACH OFFICER

AGRICULTURE CHEMISTRY (SOILS) SECTION AGRICUTLURE RESEARCH INSTITUTE TANDOJAM

Important Facts to Know

• Know the classification scheme of the US System of Soil Taxonomy

• Understand the value of learning key components of the soil taxonomy system.

• Be able to identify the distinguishing characteristics of each soil Order, and under what conditions each may be expected to exist.

What is soil classification? Give old classification of soil. Soil classification is dynamic in nature and

keeps on changing and adjusting as knowledge and understanding of the soil increase.

Geological Approach divided into two groups: Sedentary Transported The classification was further improved and

soils were groups into red soils, black soils (regurs),laterite and lateritic soils, delta soils, desert and tarai soils.

Soil

The upper layer of the earth which is composed of different thin rock particles is helpful in the growth of vegetation and plants that is called soil.

Soil profile:a vertical section of soil from the ground surface to the parent rock.

Basic Components of Soil

Soil has three basic components. 1. Solid particles like salt, mineral and organic

matter. 2. Air. 3. Water

Classification of Soils

The soil of Pakistan may be classified according to the regional basis.  Indus basin Soils About 60% of Pakistan's total land area is classified as unusable for

forestry or agriculture because it consists of deserts and mountains. Pakistan’s soils are mostly dry and have high concentrations of calcium carbonate and a low content of organic matter. The major soil groupings are Indus basin soils, mountain soils, and sandy desert soils.

74.3% of Pakistan’s soils are composed of these six types of soil:1. 30.6% Mountain/Valley: Patchy soils that are a loamy-gravelly mix2. 14.7% Rolling/hilly sandy soils3. 11.4% Loamy-clayey soils4. 6.6% Rock out-crop and loamy soils, very shallow 5. 5.8% Mainly loamy to partly gravelly soils 6. 5.2% Loamy soils

It is also true that Pakistan’s soil can be classified regionally, or according to where it is found in the county. From that perspective, there are also six soil types:1. Indus basin soils: The soils found along the current course of the Indus River are due to alluvial deposits made by that river depositing sediments every spring.2. Bongar Soils: These soils are found in the historic Indus plain and are the best soils for agriculture in the country. Usually they’re far from the present-day bed of the Indus River. 3. Khaddar Soils: Also found along Pakistan’s rivers is this soil. It formed when, every year during flood, a new layer of salty clay was deposited. 4. Indus Delta Soils: These soils cover the current Indus River delta. Most of this soil is very clayey and was developed under seasonal floodwaters. 5. Mountain Soils: These rocky soils mostly cover the highlands of northern and western areas of Pakistan.6. Sandy Desert Soils: These soils are made by the deposition of sand, layer by layer, year after year, for thousands of years. They’re found in the arid and semi-arid areas of Pakistan.

The general principles of natural soil classification systems are:

A natural system of classification should express general or universal relationships that exist in nature. One should be able to understand, remember, generalize, or predict from information obtained.

The scheme should be based on characteristics or attributes of things classified as related to their genesis. It should place similar things together on the basis of their properties.

It is technically impossible to use all of the properties of soils to classify them. Judgment based on existing knowledge must be used to determine which properties are most important.

 

The US System classification scheme contains 6 categories:

1. Order – the most general grouping2. Suborder - defined by moisture, temp,

dominating chemical or textural features

3. Great Group - by differentiating horizons4. Subgroup - three types: typical (typic),

intergrade, not one of the other two5. Family - plant growth or engineering

properties.6. Series – common name, like yours and

mine.

The US System of Soil Taxonomy

In addition to these categories, we have the soil Phase (or soil Type), which refers to surface properties such as texture, thickness, slope, coarse fragments, salinity, erosion, etc.

This is added to a series name (like Aiken clay loam, eroded phase).

Order, Sub-Order, Great Group, Sub-Group, Family, Series and Phase or Type

SOIL ORDERS (12 major units of classification according to the US 10th Approximation)

Alfisols: Relatively high base saturation; not organic rich; evidence of clay transport.

Andisols: Soils derived major properties from volcanic parent material. High P fixation.

Aridisols: Arid soils; Low in organic matter; high in salts and pH.

Entisols: Leftovers; Not well-developed even after long periods (can occur anywhere)

Gelisols: permafrost. Histosols: Soils formed from organic matter (peats and mucks).

Inceptisols: Still forming; Water is available for soil formation (e.g., glaciated soils). Mollisols: Brown-black surface horizons; High in organic matter, vermiculite or smectite clays; Base saturation usually > 50% (e.g., Iowa farm soils) Most extensive in the US (25%).

Oxisols: Highly-weathered; Only quartz, kaolinite, and Fe and Al oxides left (e.g., tropical rainforest). Spodosols: Evidence of Fe, Al, and organic matter transport; Often a whitish E Horizon (e.g., boreal forest). Ultisols: Clay transport like Alfisols, but much more acidic. Higher temperature; Often highly weathered (e.g., Southeastern U.S.). Vertisols: Mixed soils; Swelling clays, frost, etc cause lower horizons to mix with upper horizons; Often characterized by cracks.

Photo of soil profile

Aridisol Entisol

Photos courtesy of USDA NRCS, National Survey Centerhttp://www.statlab.iastate.edu/soils/photogal/orders/soiord.htm

Photo of soil profile

Gelisol Histosol

Photos courtesy of USDA NRCS, National Survey Centerhttp://www.statlab.iastate.edu/soils/photogal/orders/soiord.htm

Photo of soil profile

Inceptisol Mollisol

Photos courtesy of USDA NRCS, National Survey Centerhttp://www.statlab.iastate.edu/soils/photogal/orders/soiord.htm

Photo of soil profile

Oxisol Spodosol

Photos courtesy of USDA NRCS, National Survey Centerhttp://www.statlab.iastate.edu/soils/photogal/orders/soiord.htm

•Five of these orders exist in a wide variety of climates: Entisols, Inceptisols, Histosols, Andisols, and Vertisols. •The others are primarily a product of time.•Worldwide extent:

Aridisols 19%Alfisols 13%Inceptisols 9%Mollisols 8%Oxisols 8%Others 43%

One-fifth of world’s surface is mountainous and not classified.

Sub-Orders

Sub-Orders are differentiated on the basis of additional soil properties and horizons that are related to soil moisture, temperature, and/or dominating effects of chemical or textural features.

Sub-Orders are distinctive within a given Order and are not interchangeable. For example:

Histels Fibrists Psamments Xerepts Ustands Argids

Cryolls Torrerts Aqualfs Orthods Humults Torroxs

See sections: 7:7 through 7:18

Great Group

Soil Great Groups are sub-divisions of the Sub-Orders and have been established largely on the basis of differentiating soil horizons and other prominent soil features.

The Great Group level of taxonomy consists of the combination of 3 descriptive roots.

For example:

Argi-xer-olls – Argixerolls

Calci-torr-erts – Calcitorrerts

Hal-aqu-epts -- Halaquepts

There are 3 levels of Sub-Groups; the central (typic) concept, intergrades, and extragrades.

Family groupings are based on: 1) particle size class, 2) minerals, 3) temperature,4) rooting depth, 5) maybe others like pH, lime, cracking, particle

coatings, etc.

Sub-Group and Family

Waca series (Truckee, CA): Classification: loamy-skeletal, mixed, frigid, Andic Xerochrepts

Translation: loamy soil texture with >35% coarse fragments, mixed mineralogy, mean annual temperature <8oC, dry in summer, dry soil with Andic properties but not qualifying as an Andisol, not fully formed with light colored low organic matter A horizon.

Examples of soil classifications and what they mean:

Corbett series:Classification: Typic Frigid Xeropsamments

Translation: Typical of classification, mean annual temperature <8oC, dry in summer, sandy textured soil with minimal profile development.