Chapter 2 Basic concepts - ROOT of content

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water capacity of the soil profile. However,where such data were not available,some function of effective depth and soil texture, believed to bear a linearrelationship with available water capacity, could be used. In the former case,the set of critical values for available water capacity used to define classlimits might be such as: over 20 cm, 15-20 cm, 12-15 cm.2.4.2 The scarcity value of landThe value of a particular type of land may be increased by its scarcity,or the rarity of certain of its qualities, within a given region or country. Thisis often the position with nature reserves. In the extreme case, the presence ofa plant or animal species unique to one area may make that land virtually irreplaceable,resulting in strict protection even against highly profitable otheruses. Situations where land acquires added suitability for a particular use byvirtue of its scarcity can also arise with productive forms of use, for examplewhere dry-season grazing land is in short supply.2.5 Requirements and limitationsRequirements of the land use refer to the set of land qualities thatdetermine the production and management conditions of a kind of land use.Limitations are land qualities, or their expression by means of diagnosticcriteria, which adversely affect a kind of land use.For example, the requirements for mechanized cultivation of wheat includehigh availability of oxygen in the root zone and absence of obstructions (bouldersor rock outcrops); waterlogging and the presence of boulders are limitations.Thus limitations may be regarded as land qualities expressed in such a way asto show the extent to which the conditions of the land fall short of the requirementsfor a given use.18
2.6 Land improvementsLand improvements are activities which cause beneficial changes in thequalities of the land itself. Land improvements should be distinguished fromimprovements in land use, i.e. changes in the use to which the land is put ormodifications to management practices under a given use.Land improvements are classed as major or minor.A major land improvement is a substantial and reasonably permanentimprovement in the qualities of the land affecting a given use. A large nonrecurrentinput is required, usually taking the form of capital expenditure onstructure and equipment. Once accomplished, maintenance of the improvementremains as a continuing cost, but the land itself is more suitable for the usethan formerly. Examples are large irrigation schemes, drainage of swamps andreclamation of salinized land.A minor land improvement is one which either has relatively smalleffects or is non-permanent or both, or which lies within the capacity of individualfarmers or other land users. Stone clearance, eradication of persistentweeds and field drainage by ditches are examples.The separation of major from minor land improvements is intended onlyas an aid to making a suitability classification. The distinction is a relativeone; it is not clear-cut and is only valid within a local context. In cases ofdoubt, the main criterion is whether the improvement is within the technical andfinancial capacity of individual farmers or other landowners (including smallcommunal owners, e.g. village co-operatives). In many areas improvements suchas subsoiling, dynamiting or terracing cannot be undertaken by individualfarmers, and are therefore regarded as major land improvements; in countrieswith large farms and high capital resources coupled with good credit facilities,however, these changes may be within reach of individuals and are thereforeconsidered as minor improvements. Field drainage is another improvement thatmay or may not be regarded as major, depending on farm size,permanency of tenure,capital availability and level of technology.19
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