Land evaluation
Land evaluation is the process of estimating the potential
of land for alternative kinds of use. These uses can be productive such as
i) arable farming,
ii) livestock production,
iii) forestry or other uses such as, a) catchment protection, b) recreation, c)
tourism, d) wild life conservation.
It involves interpretation of the information from soil survey, climate, soils,
vegetation and other aspects of land with the purpose of suggesting alternative
land use. Land evaluation is done based on certain principles.
* During land evaluation, land suitability is assessed and classified with respect
to specified kind of use.
* Evaluation requires a comparison of the benefits obtained and the inputs needed
on different types of land.
* Land evaluation is a multi-disciplinary approach.
* Evaluation is made in terms of relevance to the physical, economic and social
context of the area concerned.
* Land suitability refers to the use of land on a sustained basis keeping in view
the ecosystem.
* Evaluation involves comparison for more than a single kind of use.
The land characteristics are measurable properties of physical environment that
affect the land use while land qualities (both internal and external) are practical
consequences of land characteristics that affect the plant growth. Both land characteristics
and land qualities are considered for land evaluation.
Land evaluation involves the assessment of potentials of land and soils for different
uses. This involves matching the land characteristics/qualities and crop requirements
for alternative land use.
There are many qualitative and quantitative evaluation approaches in vogue. These
are:
A) Qualitative
(i) Land capability classification- (Klingebiel & Montgomerry 1961)
(ii) Land irrigability classification (USBR, 1953)
B) Quantitative
(i) Suitability rating (Storie, 1978)
(ii) Actual and potential productivity (Requier et al., 1970)
C) Land suitability classification (Fao, 1976; Sys, 1985; Sys et al., 1961)
A) Qualitative methods
In these methods relevant parameters or factors that affect
the crop growth are selected. Level of these factors and their deviation from
optimal level (constraint) under an agroclimatic condition are compared with crop
requirements to arrive at suitability classes for each land use.
i) Land capability classification
It is an interpretative grouping of soils based on inherent
soil characteristics, land features and environmental factors that limit land
use or impose risk of erosion. Soils are grouped in 8 capability classes on the
basis of their ability to produce commonly cultivated crops. The risk of soil
damage progressively increases from class I to class VIII. Arable lands are put
in class I to IV and the non-arable in class V to VIII. There is a provision to
assign subclass on the basis of kind of predominant hazard, limitation or conservation
problem. A sub-class may be further divided into capability units according to
similarity in potential and response to management.
While land capability classification system is useful for relatively broad level
planning it needs to be supplemented by more precise evaluation for micro level
planning.
*The land capability classification is conservation oriented which considers the
negative aspects (Beek, 1981; Swindale, 1981). Yet this system is still widely
used because of its simplicity and ease of comprehension.
* The capability classification gives general idea about the capability of the
soils but does not explain specific crop performance unless supplemented by additional
information.
* This method could be followed effectively for highlighting the conservation
oriented limitations which need immediate attention and for broad grouping of
soils into agricultural and non-agricultural lands.
Frame of capability classification
* Classes
# Groups of land units that have the same degree of limitation.
#The risk of soil damage or limitation becomes progressively greater from class
I to class VIII.
# The classes show the general suitability of a land unit for agricultural use.
Class I to IV - Arable
Class V to VIII - Non-arable
* Sub-classes
These are based on major conservation problems such as:
e - erosion and runoff
w - excess water
s - root zone limitations
c - climatic limitations
* Capability unit
Groupings of one or more individual soil mapping units having similar potentials
and limitations or hazards.
a) Produce similar crops under similar management.
b) Require soil conservation or management.
c) Have comparable potential productivity.
The definitions of the different classes are given in the "land capability class
rating table" ICAR (Tejwani, 1976 in Dhruba et al., 1990).