MASHOOQ HUSSAIN ODHANO ASSISTANT RESEARACH OFFICERAGRICULTURE 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 oldclassification 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 intotwo 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 verticalsection of soilfrom theground surfaceto the parentrock.
Basic Components of SoilSoil 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 Pakistans 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 mix 2. 14.7% Rolling/hilly sandy soils 3. 11.4% Loamy-clayey soils 4. 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 classifiedregionally, 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 currentcourse of the Indus River are due to alluvial deposits madeby that river depositing sediments every spring.2. Bongar Soils: These soils are found in the historic Indusplain and are the best soils for agriculture in the country.Usually they’re far from the present-day bed of the IndusRiver.3. Khaddar Soils: Also found along Pakistan’s rivers is thissoil. It formed when, every year during flood, a new layer ofsalty clay was deposited.4. Indus Delta Soils: These soils cover the current IndusRiver delta. Most of this soil is very clayey and wasdeveloped under seasonal floodwaters.5. Mountain Soils: These rocky soils mostly cover thehighlands of northern and western areas of Pakistan.6. Sandy Desert Soils: These soils are made by thedeposition of sand, layer by layer, year after year, forthousands of years. They’re found in the arid and semi-aridareas of Pakistan.
The general principles of natural soilclassification 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 of Soil TaxonomyThe US System classification scheme contains 6categories: 1. Order – the most general grouping 2. Suborder - defined by moisture, temp, dominating chemical or textural features 3. Great Group - by differentiating horizons 4. Subgroup - three types: typical (typic), intergrade, not one of the other two 5. Family - plant growth or engineering properties. 6. Series – common name, like yours and mine.
In addition to these categories, we have the soilPhase (or soil Type), which refers to surfaceproperties such as texture, thickness, slope,coarse fragments, salinity, erosion, etc.This is added to a series name (like Aiken clayloam, eroded phase).Order, Sub-Order, Great Group, Sub-Group,Family, Series and Phase or Type
SOIL ORDERS (12 major units of classificationaccording to the US 10th Approximation)Alfisols: Relatively high base saturation; notorganic rich; evidence of clay transport.Andisols: Soils derived major properties fromvolcanic parent material. High P fixation.Aridisols: Arid soils; Low in organic matter; highin salts and pH.Entisols: Leftovers; Not well-developed evenafter long periods (can occur anywhere)
Gelisols: permafrost.Histosols: Soils formed from organic matter(peats and mucks).Inceptisols: Still forming; Water is available forsoil formation (e.g., glaciated soils).Mollisols: Brown-black surface horizons; High inorganic matter, vermiculite or smectite clays;Base saturation usually > 50% (e.g., Iowa farmsoils) Most extensive in the US (25%).
Oxisols: Highly-weathered; Only quartz, kaolinite, and Feand Al oxides left (e.g., tropical rainforest).Spodosols: Evidence of Fe, Al, and organic mattertransport; Often a whitish E Horizon (e.g., boreal forest).Ultisols: Clay transport like Alfisols, but much moreacidic. Higher temperature; Often highly weathered (e.g.,Southeastern U.S.).Vertisols: Mixed soils; Swelling clays, frost, etc causelower horizons to mix with upper horizons; Oftencharacterized by cracks.
Photo of soil profile Aridisol EntisolPhotos courtesy of USDA NRCS, National Survey Centerhttp://www.statlab.iastate.edu/soils/photogal/orders/soiord.htm
Photo of soil profile Gelisol HistosolPhotos courtesy of USDA NRCS, National Survey Centerhttp://www.statlab.iastate.edu/soils/photogal/orders/soiord.htm
Photo of soil profile Inceptisol MollisolPhotos courtesy of USDA NRCS, National Survey Centerhttp://www.statlab.iastate.edu/soils/photogal/orders/soiord.htm
Photo of soil profile Oxisol SpodosolPhotos 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 ofclimates: 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 notclassified.
Sub-OrdersSub-Orders are differentiated on the basis ofadditional soil properties and horizons that arerelated to soil moisture, temperature, and/ordominating effects of chemical or texturalfeatures.Sub-Orders are distinctive within a given Orderand are not interchangeable. For example:Histels Fibrists Psamments Xerepts UstandsArgidsCryolls Torrerts Aqualfs Orthods HumultsTorroxsSee sections: 7:7 through 7:18
Great GroupSoil Great Groups are sub-divisions of the Sub-Orders and have been established largely on thebasis of differentiating soil horizons and otherprominent soil features.The Great Group level of taxonomy consists of thecombination of 3 descriptive roots.For example: Argi-xer-olls – Argixerolls Calci-torr-erts – Calcitorrerts Hal-aqu-epts -- Halaquepts
Sub-Group and FamilyThere 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.
Examples of soil classifications and what they mean:Waca series (Truckee, CA):Classification: loamy-skeletal, mixed, frigid,Andic XerochreptsTranslation: loamy soil texture with >35%coarse fragments, mixed mineralogy, meanannual temperature <8oC, dry in summer, drysoil with Andic properties but not qualifying asan Andisol, not fully formed with light coloredlow organic matter A horizon.
Corbett series:Classification: Typic Frigid XeropsammentsTranslation: Typical of classification, meanannual temperature <8oC, dry in summer, sandytextured soil with minimal profile development.