Chapter 2 Basic concepts - ROOT of content

cslope angle, slope length, permeability, soil structure, rainfall intensity andother characteristics. Because of this problem of interaction,it is recommendedthat the comparison of land with land use should be carried out. in terms of landqualities.A land quality is a complex attribute of land which acts in a distinctmanner in its influence on the suitability of land for a specific kind of use.Land qualities may be expressed in a positive or negative way. Examples aremoisture availability, erosion resistance, flooding hazard, nutritive value ofpastures, accessibility. Where data are available, aggregate land qualities mayalso be employed, e.g. crop yields, mean annual increments of timber species.Table 1 gives an illustrative list of land qualities related to productivityfrom three kinds of use and to management and inputs.It is not exhaustive, nor iseach land quality necessarily relevant for a particular area and type of land use.The qualities listed in B and C are in addition to those of A, which may be relevantto all three kinds of use (based in part on Beek and Bennema, 1972). Theremay also be land qualities related to major land improvements. These vary widelywith the types of improvement under consideration. An example is land evaluationin relation to available supplies of water where irrigation is being considered.A land quality is not necessarily restricted in its influence to one kind ofuse. The same quality may affect, for example, both arable use and animal production.There are a very large number of land qualities, but only those relevantto the land use alternatives under consideration need be determined. A landquality is relevant to a given type of land use if it influences either the levelof inputs required, or the magnitude of benefits obtained, or both. For example,capacity to retain fertilizers is a land quality relevant to most forms ofagriculture, and one which influences both fertilizer inputs and crop yield.Erosion resistance affects the costs of soil conservation works required forarable use, whilst the nutritive value of pastures affects the productivity ofland under ranching.Land qualities can sometimes be estimated or measured directly, but arefrequently described by means of land characteristics. Qualities or characteristicsemployed to determine limits of land suitability classes or subclassesare known as diagnostic criteria.15