The below mentioned article provides a note on land use capability classification.
Introduction to Land Use Capability Classification:
For preparation of land use capability classification it is important to carry out a detail soil survey of the area. Soil survey includes the study and mapping of soils of the watershed with full of their natural resources. It provides a complete information about soil and other natural features, while a soil map indicates only mapping unit.
A soil survey report along with soil map provides the following information about the watershed:
1. An inventory of soil resources of the watershed; and
ADVERTISEMENTS:
2. A means of classification, describing and showing the aerial distribution of the soil in the watershed.
The inventory of soil resources can be used for following purposes:
1. To show the potential productivity of the watershed.
2. To indicate when and how production can be increased under different sets of management system in a watershed.
ADVERTISEMENTS:
3. To estimate fertilizer requirement of the crop of a particular region; and
4. To compute and predict the adaptability of soils for various farming practices such as crop cultivation, pasture growing, forestry etc.
In brief, a soil survey acts as a tool for helping the farmers, foresters, engineers, planners, development agencies and other users for decision making about the land use and management practices.
Mapping Unit to Demarcate the Soil Boundaries:
The soil series, soil types and soil phases are the units of classification. If all these units are used as mapping unit to demarcate the soil boundaries in the field within the watershed and finally on the soil map, it becomes very difficult to show, because a very small area of other soil unit may occur as a scattered points in between.
ADVERTISEMENTS:
Hence, for practical purposes while demarcating the soil boundaries in the field and plotting them on the soil map, it is necessary to ignore the inclusions up to 20% of other kinds of soils. The soil unit thus allowing minor inclusions of other kinds for mapping is known as mapping unit.
The following criteria can be followed for establishment of mapping units:
(i) It should be as homogeneous as possible. However, it is not essentially be the same as distinguishing soils with uniform characteristics, but the variation within mapping unit is kept within the defined limits and the kind of variation should be consistent within all mapping units.
(ii) The grouping should be of practical values.
ADVERTISEMENTS:
(iii) It must be possible to map the units, consistently.
(iv) The mapping must be accomplished in a reasonable time and with only such equipments, that can be used in the field very easily.
(v) The soil characteristics used in mapping must be the main, visible and tactile properties such as colour, texture etc.; however, the properties such as plant nutrients that cannot be observed directly, should not be mapped.
(vi) Relatively, the stable soil properties such as texture and lithology should be used to define the taxonomic units, rather the properties which changes rapidly according to the management.
ADVERTISEMENTS:
The mapping units are classified as simple and compound. In which, the simple mapping units are those which contain only one taxonomic unit of soil. It produces the map of greatest predictive value such as soil series, soil type, soil phase, soil variant etc. The compound mapping unit includes two or more taxonomic groups of certain soils, such as soil association, soil complex etc. The simple and compound mapping units are shown in Table 22.1.
Soil and Land Use Capability Classification:
Soil survey maps and reports are the tools for a system to divide the entire watershed into various classes as per soil and land use capability features.
The land use capability classification is a system under which lands are classified as per their potential ability to produce the yield. This system of classifying the land is based on the potential ability of different kinds of soil for agricultural purposes. It is also a practical grouping of soil based on various soil limitations which show the risk or damage. Land classification is mainly for the use of soil according to various limitations and providing adequate protection from erosion and other means of deterioration.
An area where soil depth is more, well drained and includes a stable structure, and slope varies from 1 to 3% can be used with little danger of erosion or loss of productivity has few limitations and greater capability for its use, based on which a particular soil can be put in a class. On the other hand, an area with shallow and poorly drained soils or with steep slopes has many limitations and limited capability for use, is kept in another class for which it is fit.
Basically, the two terms are used in this classification which are described as below:
(1) Capability, and
(2) Limitations
It is the potential ability of the land for use in specified way or with some specified management practices, given as under:
i. Arable use of land for taking the crops without adopting soil conservation practices.
ii. Arable use of land with various restrictions cither about the choice of crops to grow, or soil conservation practices to be used.
iii. Grazing of improved pastures.
iv. Grazing of natural pastures or the woodland.
v. Land use for recreation, wild life conservation, water harvesting etc., when no other use of land is possible.
A land of given capability class has certain potential ability for some specified use and not for all the classes below it. For example – a land which is suitable for growing the crops without soil conservation practices, which is the feature of Class I, cannot be applied to other classes. Similarly, the land which is used for grazing, forestry and wild life but not for growing crops, is preferred to keep in the classes from V to VIII.
A capability class does not indicate the best use of land, but indicates only to the range of use, under which each area could be kept. The discretion is left to the farmer or to his advisor.
Factors Determining Land-Capability:
The major factors determining the land capability are the soil characteristics including texture of the top soil, effective soil depth, permeability of top and sub-soil and associated land features, e.g. the slope of land, extent of erosion, degree of wetness and susceptibility to overflowing and flooding.
The grouping of soils into different capability classes is mainly done on the basis of their capability to produce common cultivated crops and the pasture plants without deteriorating the land, for a long period.
The land-capability classification is based on the intensity of hazards and the limitations. The land- capability classes are from the best and most easily fanned land to the land which has no value for cultivation, grazing or forestry, but may be suitable for wildlife, recreation or for watershed protection. Overall, all the lands fall into two broad categories, i.e. one suitable for cultivation and for other land uses; and other land category is not suitable for cultivation, but may be suitable for other.
Urban Land Capability:
Hannam and Hicks (1980) developed the urban land capability classification based on the soils, landform, drainage, erosion and geology; and evaluating them in relation to their possible urban use. On the basis of classification the urban capability maps can be prepared to indicate the physical constraints in light of maximum urban use. The derived maps can be used for using management and protective measures required for degraded lands.
The urban land capability is evaluated on the basis of physical data of the area.
The important physical data needed for classification are listed below:
i. Geology
ii. Landform
iii. Slopes
These are described as under:
i. Geology:
It includes the data on general geological information’s such as landscape, soils, terrain and the soils subject to slope instability. The soil structure, rock types etc., are also considered as geologic data for classification.
ii. Landform:
The landform of an area affects the land capability directly and indirectly, both. Under this group of data the topographic variations due to slopes, relief, natural watercourses and catchment/basins features which affect the cost of urban development, directly, are the main.
iii. Slopes:
The slope makes a kind of topographic difference in the landscape. It is considered as one of the main parameters for classification of urban land. For this purpose the entire land is divided into various segments based on the slope. The slope group may be 0-1%, 1-5% etc.
The land slope affects the establishment of population; and accordingly their use intensity also gets affected. Also, the slope feature of the area affects the land use pattern. The slope divides the land use into intense density, medium density and low density land use patterns.
Urban Capability Classes:
These classes are grouped under five primary classes, presented in Table 22.2. Depending on the requirements for a specific purpose, these classes can further be sub-divided into different sub-classes on the basis of limitations affecting their uses. In this classification the classes are indicated by subscript, which indicates a particular limitation. These classes are shown in Table 22.2.
As example, the sub-class B-sv represents the land with moderate physical constraints on slope and shrink-swell characteristics of the soil to urban development. Similarly, the sub-class E-m represents the constraints about mass movement hazard. In this approach, the entire area is divided into a number of homogenous units, which have been evaluated on the basis of their potential for urban land use and management.
These classes can help the planners to assess the development proposals for the land uses compatible to the site conditions. The urban capability classification is also useful for regional level planning purposes. The steps involved in urban capability assessment are presented in Fig. 22.1.
It may be defined as the land features/characteristics which have adverse effect on potential capability of the land. The limitations can be permanent or temporary. Permanent limitations refer to those land characteristics which cannot be easily modified by minor land improvement works.
The permanent limitation includes following land characteristics:
i. Land slope
ii. Soil depth; and
iii. Liable to flooding
Temporary limitations can be removed by adopting proper land management practices. These limitations are not used as a basis for classifying the land.
The temporary limitation includes the following characteristics:
i. Soil nutrient; and
ii. Drainage impendence.
Lands are classified on the basis of permanent limitations. In classifying the land if any one limitation is sufficient to reduce the land productivity of a given class, then that should be allocated to that particular class.
Capability Unit for Classifying Lands:
Capability unit is defined as grouping of one or more individual soil mapping units containing similar potential ability and limitations. Soils within a given capability unit can be allowed for –
1. Same crops.
2. Use of similar treatments and management practices for conservation; and
3. Comparison of productive potential.
Land capability unit is used for classifying the lands according to their capability. Within a particular subclass, the land which is suitable for the same kind of management and conservation practices, is counted as land capability unit for the given management and conservation practices. A land may have the same capability and sub-class, but may not respond to the same treatment due to some individual differences.
The use of same treatment could be harmful, therefore, the land capability unit should be essentially uniform regarding all major characteristics, which affect the management and conservation practices, both.
Land capability units are denoted by ordinal numerals and letters which are placed as subscript to denote the sub-class in capability notation.
Example:
Class IIIs indicates that the land has severe soil limitation, which may be due to one of the following reasons:
1. Presence of sand and gravel layer in the sub-stratum.
2. Wetness caused by poor drainage or flooding.
3. Slow or very slow permeability of sub-soil or sub-stratum.
4. Erosion hazards.
5. Unfavourable soil texture or excessive gravel.
6. Presence of fine or moderately fine textured surface soil.
7. Caused by salt or alkali.
8. Presence of pebbles, stoniness or rocks.
9. Poor root penetration clue to shallow soil depth over bed-rock or hard pan.
10. Low soil fertility or toxicity.
Land capability sub-classes are formed on the basis of extent of limitations regarding the land use. However, the planning of land for various uses should not be done based on the limitations because limitation shows the difficulty only; to the kind of hazard or problems it does not indicate. Within a land capability class, the sub-classes identify the kind of limitations of hazards.
For example Class III includes those lands which are suitable for cultivation only, but may be subject to severe problem of water erosion or wind erosion on smooth land, water logging problem, overland flow or presence of bed rock at shallow depth. Each of these hazards can be used to form a separate sub-class.
There have been recognised following four kinds of land capability sub-classes:
1. Sub-Class (e) – This sub-class includes those soils which have erosion problem or susceptible to erosion and past erosion has damaged the field. This sub-class is indicated by the notation IIe, in which ‘e’ is denoted for erosion problem.
2. Sub-Class (w) – This includes those soils in which presence of excess water is the major problem for their use. Poor drainage, wetness, high water table and overland flow are the limitations, used for deciding the soil to put under this sub-class. This sub-class is indicated by IIw, in which ‘w’ indicates the hazard caused by water.
3. Sub-Class (s) – This sub-class is referred for the soil limitations existing in the root zone, which may be the shallow root zone, presence of stones or hard pan, low moisture holding capacity, low soil fertility, salinity or alkalinity problem etc. Sub-class (s) is indicated as IIs, in which ‘s’ denotes the soil’s limitations.
4. Sub-Class (c) – This sub-class is formed based on the climatic limitations. The climatic limitations may be a high or low rainfall pattern, high wind velocity, temperatures etc. Land capability sub-class (c) is designated as lie, in which ‘c’ is used for climatic limitations affecting the land use.
The chart showing the land use capability classes, land capability sub-classes and land capability unit is shown in Fig. 22.2.
Parameters Used for Land Capability Classification:
The followings are the main parameters, counted for deciding the land to keep in a particular land use capability class:
1. Effective Soil Depth:
It is the thickness of soil existing above the bed rock or impermeable layer. For categorizing the land suitable for a particular class, the effective soil depth is divided into five groups, given as under (Table 22.4).
2. Texture of the Surface Soil:
The soil texture indicates the proportion of sand, silt and clay contents in the soil. For LUC classification point of view, this feature is grouped in eight classes, shown in Table 22.5.
3. Permeability of the Sub-Soil:
In usual way it is expressed as the rate of water flow as ‘mm per hour’ through undisturbed saturated soil under a water head of 12.5 mm. For LUCC, the permeability of sub-soil is divided into 8 groups given in Table 22.6.
4. Physical Characteristics of Surface Soil:
The physical characteristics of top soil such as compaction, cloddiness etc. are also taken into consideration for land use classification. These soil feature are divided into two classes as shown in Table 22.7.
5. Erosion:
For grouping the lands in different capability classes, the erosion is counted in terms of depth of soil removed from the land surface. It is divided into following four classes for categorizing the land, given in Table 22.8.
6. Wetness:
The soil wetness is classified into three groups, as given in Table 22.9.
7. Slope:
It refers to the general slope of the land, divided into following categories (Table 22.10).
8. Available Moisture Content:
It is denoted as the depth of water available in root zone depth, i.e. in 150 cm soil column from the top soil surface. The range of available moisture capacity of the soil is grouped under five classes (Table 22.11).
9. Drainage:
The features of land drainage are determined on the basis of surface characteristics of the soil, like colour etc. The classification of drainage status is grouped under four classes (Table 22.12).
10. Salinity:
The soil salinity is classified in four classes based on their effect on the crop yield. Salinity classification is given in Table 22.13.
The parameters, described above are used to evaluate the capability of land under a certain set of circumstances. In order to make the land classification as per their capability limit, the collection of data on above parameters is most essential, which should be done in very-very precise way.
Identification of Classes in the Field:
The soil mapping units prepared during soil survey work are used for identifying different land capability classes. Land allocation in a particular capability class is done on the basis of preparing a CONVERSION TABLE (Table 22.14), which shows the kind of limitations that can be accepted for a particular class. For example – if soil erosion hazard is there in the field, then it should be decided to assign the class based on erosion hazard.
Similarly, slope is also taken for classification. The slope of class I land should not exceed 1%, Class II 3%, Class III 6% and so on. Likewise, if productivity is related by the soil depth, then effective soil depth is normally taken as 150 cm for class I: 100 cm for Class II etc. Of every land characteristics, the value for each eight classes should be determined for identifying the classes.
Once, the conversion table has been prepared, the allocation of mapping unit of a given soil, suitable to a particular capability class and sub-class becomes easy.
The preparation procedure of conversion table is given as under:
(i) Put the finger in the box of conversion table of class I with limitation 1 (texture) and go ahead until the observed texture at the site is continued.
(ii) Now, move down for second limitation (soil depth). If soil depth is 90 cm or more, put it in Class I, if it ranges from 45 – 90 cm keep in Class II; and so on.
(iii) Go for third limitation (slope), trace the finger forward until the observed slope angle at the site is reached, say 3%.
(iv) Continue this process for the whole limitations.
(v) If detail soil survey map and reports are available, then capability classification can also be prepared in the office. However, before taking any decision about the kind of use to which the land can be put in a particular class, it is very important to test it in the field by means of conversion table, and then allocation should be done for each soil mapping unit to a suitable capability class.
Land Capability Classification for Indian Ravine Lands:
Tejwani and Dhruvanarayana (1961) formulated the land capability classification for Indian ravine lands, based on the percent land slope and gully erosion hazard, as these two characteristics influence the land use of such areas, severely. The land-capability classifications of ravine lands is shown in Table 22.15.
Land Capability Classification for Western and Eastern Ghat Hills:
Basu (1956) made following classification of hills of Western and Eastern ghats of India, based on the percent land slope and soil depth, mainly. It is given in Table 22.16.
Treatment Oriented Land Capability Classification:
In this classification the land capability is assessed in terms of risk associated to the cultivation of land. The lands are classified as per suitable treatments for them. This classification system was developed in Taiwan and tested in the hilly tracts of Jamaica by Sheng (1972 a). The classification criteria was formulated on the basis of land slope and soil depth as treatment risks.
The range of slope and soil depth, suitable for different treatments are mentioned as under:
Various classes are described as under:
Class C1:
It includes the land with the slope up to 7° and soil depth is normally greater than 10 cm. Such lands can be suitably treated with the practices of contour cultivation, strip cropping, broad base terraces etc. This class lands are also suitable for tillage practices.
Class C2:
The land slope ranges from 7 to 15°, and soil depth is more than 20 cm. Such lands are recommended for the treatments of bench terracing etc.
Class C3:
The land slope varies from 15 to 20° and depth of soil is more than 20 cm. The use of bench terracing in deep soil regions and construction of silt pits on shallow-soils are recommended for land treatments.
Class C4:
Includes the land with the slope ranging from 20 to 25°, and depth of soil is more than 50 cm. The construction of bench terrace is recommended for land treatment and performing of all agricultural operations, manually.
Class P:
In this class the lands are characterized by the slope ranging from 0 to 25°. The soil depth is very shallow to perform cultivation activities. This class lands are recommended for improved pasture system along with rotational grazing, but where land is in wet condition, zero grazing is recommended.
Class FT:
Slope of land is found in the range of 25 to 30°, and soil depth is more than 50 cm.
For this class land, the following treatments are recommended to follow:
(i) Use of tree crops with bench terracing.
(ii) Inter-terraced areas with permanent grass.
(iii) Use of contour planting.
(iv) Construction of diversion ditches.
(v) Use of mulching practices.
Class PF:
The land slope is in the range of 0 to 25°. Lands are sufficiently wet and liable to get affected by flood; lands are also in stony form. This class lands are recommended for pasture farming for those areas where some soil depth is available.
Class F:
Slope is more than 25°. The lands are wet and stony. These are recommended for forest development.
Soil and Water Conservation Practices for Cultivation Lands:
As per land use capability classification the total geographical lands are classified into eight classes starting from class I to class VIII, in which class I to class IV lands are suitable and from class V to class VIII lands are not suitable for cultivation point of view.
Although, the lands falling under class I to class IV are suitable for agricultural operations, but they also have some limitations regarding their use without use of suitable soil & water conservation practices. The most suitable practices for them are cited in Table 22.22.
Classification of Gullies as per Land Capability:
Each gully has an independent catchment with a regular stream or drainage system. In drainage basin each and every gully has a definite side slope, bed width and depth in a regular way.
For example – in the upper reaches of drainage basin, the gullies are normally wide and shallow with varying side slopes; in middle usually deeper, wide and with uniform side slope up to about 15%; and at the lower portion it is similar to the main river characterized by greater depth, steep side slope and intricate branch gullies.
As per Soils-Survey Manual, the slope classes and the susceptibility to erosion hazard by active gullies have been modified to suit the conditions of ravine lands. In ravine, the slope of the land and nearness of the gullies are the most important and dominant factors, which vary widely and influence land capability. The specifications of land capability classification for ravine lands, as influenced by the land slope and the gully erosion hazard, are presented in Table 22.23.
The gully erosion is the accelerated soil erosion, is clearly visible to naked eyes. It affects the soil productivity; restricts land use and damage the roads, fences, buildings and several other properties existing right up the gully. The sides of gully are relatively steep; and behave like a watercourse with ephemeral flow during heavy or extended rainfall.
The eroded soil mass from gully area can cause siltation of fence lines, waterways, culverts, dams and reservoirs. And the suspended sediments in water flow, which if contains nutrients and pesticides, then adversely affects the water quality. The fine and colloidal clay particles, which are in suspension form can clog the aquifers, pollute the watercourse and can affect the aquatic life, too.
British Land Capability Classification:
The British Land Capability mapping is an adaptation of USDA method. It assesses the capability of land based on the known relationship between crop production and management and the physical factors of soil, topography and climate. Principally, it is the approach in which land is grouped on the basis of qualitative and quantitative measures of the limitations related to the land capability. In British Land Capability Classification total seven classes have been recognized.
In which class-1 includes very wide range of use with few limitations; and remaining six classes suffer from increasingly severe limitations, as result they are progressively less suitable for their potential uses.
The land capability sub-classes are identified on the basis of one or more permanent or semi-permanent physical features that limit the production. These sub-classes are denoted by the letters w, s, g, e and c with the relevant class number (e.g. 2w or 6gs). Descriptions of the seven classes are outlined in Table 22.17.
Sub-Class Limitations:
These are outlined as under:
1. Wetness (w):
This type of limitation is expressed by the letter ‘w’. This sub-class includes the interactions between soil properties, relief and climate resulting into wet soils, which cause the problems of delayed growth, compaction and puddling by farm machinery, poor root development, asphyxiation, de-nitrification etc.
The wetness may be due to following reasons:
i. Low permeability, especially in fine textured soils (clays).
ii. Impermeable soil layers.
iii. High groundwater table.
iv. Flushing by springs.
v. Flooding from streams and rivers; and
vi. High rainfall.
2. Soil Limitations (s):
This is denoted by the letter ‘s’. The shallowness, stoniness, poor soil texture and structure and inherent low fertility are the main soil limitations. The characteristics shallowness affects the capacity of available water, restrictions in rooting depth and inadequate nutrient uptake. The tillage operation (ploughing) becomes impractical when bedrock is very near to top soil surface.
The stony soils affect the plant growth and farm operations in addition to obstructions in mechanized harvesting of root crops. Also, there is reduction in water holding capacity and nutrient uptake in case of stony soils. Similarly; the texture and structure affect the soil drainage and permeability. The lower fertility level of soil is very difficult to change by management practices; due to this reason it is also considered as a physical limitation.
3. Gradient and Soil Pattern Limitations (g):
The letter ‘g’ is used for denoting this limitation. The gradient (slope) causes significant effect on mechanized farming, mentioned in Table 22.18.
4. Liability to Erosion (e):
The wind and water erosions are the main. In which, wind erosion is prominent in sandy or light peat soils especially when vegetative cover has been removed from the soil surface. The water erosion may be the coastal erosion, sheet erosion, rill erosion and gully erosion on steep bare slopes and stream bank erosion.
5. Climatic Limitations (c):
It refers to the difference in macroclimate affecting the land capability. On this limitation the emphasis is given about water balance and temperature during main part of the growing season. Total three climatic groups have been recognized about climatic limitations as shown in Table 22.19.
In above climatic grouping the followings assumptions are taken into consideration:
i. The classification is mainly for agricultural purposes.
ii. The assessment of capability is under moderately high level of management; and not necessarily under its present use condition.
iii. If the lands suffering from such limitations, which can be removed or reduced at acceptable cost, then they can be graded on the basis of remaining limitations.
iv. Capability classification may be changed, if by any reclamation projects the previous limitations have been changed, permanently.
v. Within a given class the soils may differ regarding their management and fertilizer requirements, but can be grouped together because they possess similar limiting factors.
vi. Within a specified sub-class the soils involve different management requirements.
vii. The system is based on permanent or semi-permanent physical limitations; but if there is severe chemical limitation then it can also be recognized as the soil limitation.
viii. The factors such as distance to market, road access and farm structure are not considered; although they affect the decisions about land use.
ix. The classification has flexibility about the point that if there is new data or information has been acquired then classification may be changed.
x. This classification does not stand for soil suitability classification for specific crop, as result further interpretation of soil maps is required for such purposes.
Guidelines for Recognition of Capability Classes:
A. The specific features of different capability classes are summarized in Table 22.20.
B. Limitation of different sub-classes – This is summarized in Table 22.21.
