Land Capability is a kind of economic evaluation of land based on its present productivity and limitations for agricultural production. Two classification systems have been evolved to asses land capability of Bangladesh - one by the soil resources development institute (SRDI) for the whole of Bangladesh except chittagong hill tracts and the other for the Chittagong Hill Tracts by the Forestal Team.
The classification designed by the SRDI is to suit special floodplain condition of Bangladesh. There are two levels of generalisation which are recognised: Land Capability Class and Land Capability Subclass. Land Capability Class is identified by Roman numerals I to V. Class I land (very good agricultural land) has least limitation for crop production throughout the year and a relatively wide range of agricultural use. Class II, III, IV has increasingly severe limitations for crop production and increasingly great effort is required to produce satisfactory crop yield. Class V (very poor and non-agricultural land) is considered unfit for economic agricultural use.
At the second level of generalisation, the Land Capability Subclasses based on some dominant kinds of limitation for agricultural use are grouped together. Because of seasonal flooding of the land in Bangladesh a primary separation has been made between lands that are subject to seasonal flooding and those which are not. These are termed major subclasses. They are indicated by capital letters: D for land lying above normal flood level; W for land subject to flooding for part or throughout the year.
Within the major subclasses, ordinary subclasses are differentiated. Ordinary subclasses are indicated, where appropriate, by small letters added after the major subclass designations. The following ordinary subclasses are recognised during reconnaissance soil survey in Bangladesh: d - Soils restricted in use due to draughtiness in the dry season; e - Soils restricted in use due to erosion hazard (on slopes); r - Soils having irregular local relief hindering irrigation, drainage or tillage; s - Soils having excess soluble salts; t - Soils containing chemical compounds, toxic or potentially toxic to plants; w - Soils restricted in use due to excess water (in the dry season in major subclass W soils, in the monsoon season in major subclass D Soils); x - Fresh alluvium or very young alluvial soils restricted in use due to poor physical condition and/or susceptibility to river erosion or burial by further fresh alluvium; z - Soils having a hazard of crop loss or damage by rapid flow of flood water.
In the case of land capability class I, the major subclass D and W are recognised but ordinary subclasses are not. In other classes (class II to class V) major subclasses followed by ordinary subclasses are used where appropriate.
Descriptions of Land Capability Classes in Bangladesh is as follows:
Class I: Very Good Agricultural Land. Soils in this class have no to slight limitations for crop production throughout the year and has the widest range of agricultural use.
Class II: Good Agricultural Land. Soils in this class have none to slight limitations for crop production during most of the year, but moderate limitation during the remainder of the year.
Class III: Moderate Agricultural Land. Soils in this class have moderate limitations for crop production throughout the year or severe limitations for crop production during one major season of the year and slight to moderate limitations during remainder of the year.
Class IV: Poor Agricultural Land. Soils in this class have severe limitations for crop production throughout the year.
Class V: Very Poor and Non-agricultural Land. Soils in this class have very severe limitations, which either make crop production impossible or very hazardous or cause extremely low yields.
The land capability assessment for the floodplain areas of Bangladesh shows the proportion of different classes as follows: very good agricultural land 1.3%, good agricultural land 36.7%, moderate agricultural land 40.5%, poor agricultural land 16.1%, and very poor agricultural land 5.4%.
Land resources development done in recent years has made some changes in the above pattern for which latest data are not available. However, more than half of agricultural land is still in the moderate and poor category.
The land capability classification adopted for the Chittagong Hill Tracts is based on depth of soil and slope of the land. The classification is categorised into four classes: A, B, C and D. The limitations on agricultural use of land become progressively greater from class A to class D.
Class A: land in class A has very few limitations that restrict crop production. Land in this class can be used for a wide range of crops and extensive modern agricultural management can be practised for higher crop production.
Class B: land in class B has moderate limitations that reduce the choice of crops or require the adoption of soil conservation practices to prevent land degradation.
Class C: land in class C has severe limitations that reduce the choice of crops or require adoption of special intensive soil conservation practices. Limitations in Class C land include slopes between 20% to 40%, a high susceptibility to erosion, a low moisture holding capacity and/or shallowness of the soil.
Class D: land in class D has very severe limitations that restrict crop production. The use of this class of land is almost impossible because of very steep slope and a high susceptibility of erosion, often aggravated by low moisture holding capacity, low fertility and/or shallowness of the soil.
The total area of the Chittagong Hill Tracts is 13,237 sq km. The area assessed for land capability includes unclassed state lands which occupy 10,121 sq km out of which 535 sq km is occupied by settlement and waterbodies (mainly Kaptai Lake). The reserved forests occupying about 3,096 sq km (23.3%) of the Chittagong Hill Tracts were excluded from assessment of land capability.
The land capability assessment of the Chittagong Hill Tracts show the proportion of different classes as follows - Class A: good agricultural land 3.2%, Class B: moderate agricultural land 2.8%, Class C: poor agricultural land 15.6%, and Class D: very poor and non-agricultural land 78.4%.
The land capability assessment for the Chittagong Hill Tracts indicates that it has only 6.0% good and moderate agricultural land, 15.6% poor agricultural land and 78.4% very poor and non-agricultural land.
A generalised land capability map drawn by the Forestal Team shows that the better agricultural land is much more extensive in the northern half of the Hill Tracts than the southern half. [M Rezaur Rahman]