...And QuestionedAuthor(s): Colin ClarkSource: Area, Vol. 7, No. 2 (1975), pp. 109-110Published by: The Royal Geographical Society (with the Institute of British Geographers)Stable URL: http://www.jstor.org/stable/20000977 .

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Comment 109

Maps produced using the new soil classification should have greater utility to all users, since precision is increased, and an assessment will be made of the proportions of different taxa within map delineations. If, for example, a map delineation contains 50 % or more of recorded profiles attributed to one soil series it will bear the symbol for that series, but the record which accompanies the map will attempt (as well as is possible

with the funds available) to state the proportions of this and other taxa which are present. This was more difficult under the old classification because the taxa themselves were not precisely defined.

Since the new classification is definitional it can be arranged in the form of a key, so that it must include all soils likely to be encountered. The problem here is not

whether unknown soils can be fitted into the classification, but whether or not the resulting classes are appropriate to the purpose of the classification. All classifications are interim-including botanical classification, which has been greatly modified since Linnaeus's day-not only to accommodate new species, but also in response to chang ing ideas about the relationships between the various taxa.

The figures may show that educational establishments are the chief buyers of these maps, but it should be pointed out that most Survey publications are distributed to regular users in the Ministry of Agriculture, Fisheries and Food, which commissions and funds the Survey.

Reference

Avery, B. W. (1973) ' Soil classification in the Soil Survey of England and Wales ', J. Soil Sci. 24, 324-38

...and questioned

Colin Clark (University of Exeter) writes:

Frank Courtney has highlighted some of the problems of the new soil classification,' pointing out that statistical reliability of soil maps should be made. He gives an example of the Sherbourne Soil Series mapping unit as being unimodal.2 This example is within mapping unit variation; but what of between unit variation which is funda

mental to any classification? First, although PCA (Principal Components Analysis) was used successfully by Courtney for a single unit its use between units presents problems. Had he for example included samples from the Atrim Series, which in East Somerset is laterally continuous with the Sherbourne Series, his component scores would have reflected a soil catena, making ' between' variation less than that implied in the taxonometric study.

Accepting that soils have to be statistically defined introduces problems of cost and subjective definition of a modal cluster.3 Identification of taxonometric clusters is subjective especially if the points are identified on components diagrams to begin

with.4 An alternative method would be to use a continuous taxonomic algorithm which at the same time can be displayed to reveal probable discontinuities. The single linkage method5 is the only sorting strategy that fulfills the criteria of Jardine and Sibson,6 in particular in being a continuous function. Thus the technique is suitable for the recognition of soil catenas. With subgraph representation7 clusters of samples (soil mapping units) could be given a measure of connectivity and isolation. The articulation points on the subgraphs may represent intermediate soil types.

While the ultimate delimitation of soil series would still be subjective, variation between these units may be assessed and the relations amongst soil groups clarified. If a key could be constructed for use on a computer, the taxonomic position of a ' monster' soil could be rapidly clarified.

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110 Comment

We are in a period of reassessment of existing techniques and standards: that of classifying soils is long overdue, especially with regard to soils hitherto considered of

marginal use. Data used in a classification should be freely available to farmers. If activity ratios of cations, cohesive strength, drainage and the like were included as characters in the classification it could be of use to land use planners and farmers; in short a marketable classification.

Notes

1. F. M. Courtney, 'New soil classification: Was it worth it?', Area 6 (1974) 3, 205-6 2. F. M. Courtney, ' A taxonometric survey of the Sherbourne soil mapping unit', Trans.

Inst. Br. Geogr. 58 (1973) 113-24 3. Courtney, 1974, op. cit. 4. F. A. Bisby, 'The role of taximetrics in Angiosperm taxonomy. 1, Empirical comparisons

of methods using Crotalaria L. ', New Phytol. 72 (1973), 711 5. R. R. Sokal and P. H. A. Sneath, Principles of numerical taxonomy (San Francisco, 1963) 6. N. Jardine and R. Sibson, ' The construction of hierarchic and non-hierarchic classifications',

Computer J. 11 (1968) 177-84 7. M. Wirth, G. F. Estabrook and D. J. Rogers, ' A graph theory model for systematic biology,

with an example for the Oncidiinae (Orchidaceae) ', Syst. Zool. 15 (1966) 59-69

2. Land parcellization C. J. Dixon (City of London Polytechnic) writes:

The paper by Dr Igbozurike raises a number of important points concerning the relationship between land tenure and agricultural systems which are ignored by the

measure of ' parcellization ' that he outlines.' In making any assessment of the useful ness of such a statistical device it is essential to be clear what is being measured, what we expect to find, and what is the relevance of the technique to agricultural geography.

Dr lgbozurike's exposition of the 'land parcellization index' is not clear about the method of computation with respect to the derivation of D,; in the text this is defined as 'the aggregate distance between land fragments: the actual total distance covered by the operator in making a single round trip that takes in all his parcels '.2 From the text and the diagrams, three possible methods could be used to compute Dt: a round trip, starting at the farm and taking in all the fragments in a circuit ending at the farm; the aggregate of return trips from the farm to each fragment; and a one-way trip between the farm and each holding. Particularly puzzling is the difference in the apparent composition of Dt in the underdeveloped and developed cases shown in the figures.3 It is however apparent that all the methods could be used, and each may be relevant in particular instances.

Of more fundamental importance is the basic premise behind the index. In essence the measure is one of efficiency of movement, but also, by implication, of efficiency of practice. ' Generally speaking, the larger the dimension of an agricultural unit, the more viable and stable the unit is likely to be,' says Igbozurike,4 and he characterizes one farm's ' parcellization problem' as 'more serious than' another's.5 This implies that fragmentation is undesirable and reduces efficiency, a view which has been repeatedly questioned in the literature of land tenure.6

The fragmenting of farm holdings has many causes.7 The literature does not always distinguish between the causes of fragmentation as a static phenomenon and fragment ation as an ongoing process, where land is held in an increasingly large number of parcels of declining size. Fragmentation is treated as having an origin itself, usually stemming from factors outside the agricultural system, especially socio-economic practices such as inheritance, often accentuated by population pressure. Seen in this

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