2. THE NATURE AND PURPOSE OF LAND EVALUATION

2.1 What is land evaluation?

Land evaluation is the process of assessment of land performance when used for specific purposes, in order to identify and compare promising kinds of land use. Essentially it is a procedure for comparing land with land use, where land refers to all the factors of the physical environment, including climate, landforms, soils and vegetation. More precisely, land evaluation involves comparison between the environmental requirements of various kinds of land use and the properties possessed by different areas of land.

Take, as a simplified example, the growth of a single tree or crop species. Clearly, what grows well in a semi-arid environment will not do so in the rain forest zone, and vice versa. For each plant species there is a range of conditions which are highly favourable for its growth, a wider range within which it will grow but not so well, and sets of conditions (e.g. too wet or too dry, too acid or too alkaline) in which it will not grow at all. In the terminology of land evaluation, these sets of environmental conditions are, respectively, highly suitable, suitable and not suitable for the tree or crop. Many environmental properties, e.g. temperature, moisture availability, soil reaction, drainage, need to be assessed in this way, and account taken of their interactions.

There is a second way of looking at the comparison between land use and land, that of taking a specific area of land as the basis. Any given area of land possesses a distinctive set of properties, of climate, soils, vegetation, etc. Under such conditions there will be some trees or crops which grow very well, some which grow satisfactorily, and others which fail and die. That is, taking a specific area, it will be found that different plant species are highly suitable, suitable, or not suitable for the environment of that area.

The same approach to that outlined above for a tree or crop species considered in isolation can be applied to cropping systems (rotations, intercropping, etc.); to crops grown under specified management conditions (e.g. with or without fertilizer); or to combinations between trees, crops and pastures. Any land use system, described in as much detail as the intensity of the study requires, can be evaluated as to its suitability in different environments. The term employed to refer to a defined land use system, taken as the subject of land evaluation, is a land utilization type.

These simplified examples illustrate the potential of land evaluation for answering questions of two kinds:

1. For a given kind of land use, where are the areas to which it is best suited?

2. For a given area of land, what is the most suitable use?