4. THE INTERPRETATION OF SOIL SURVEYS FOR PRACTICAL ...

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We therefore think that soil suitability classification is the central part of soil survey interpretation.We consider soil quality classification and soil crop response classification asbeing part of this kind of soil groupings (cf KELLOGG, 1961). Soil suitability classificationindicates the suitability of a soil for a more or less specific use, or for an improvement ofthe soils. Therefore in the one case we speak of a suitability of use, whereas the other iscalled suitability of improvement. Fig. 7 indicates how suitability of use and suitability ofimprovement are connected. In this figure the possibility of a change of the profile, for instanceby deep-ploughing is also to be considered. This change of the profile consists of achange in the soil itself, so that in this case a new classification of the fundamental characteristicsof the soil must be made.WITH SOIL IMPROVEMENTPotential land use withirrigation and or dramgePotentrol land use withoutirrigation and OT droinage--fSoil- imwovementlNew soil map / IOrtginol soii mopFig. 7. Suitability of use and suitability of improvementt4WITHOUT SOIL IMPROVEMENTSuitability of useSuitability oftmmvement!%tential kmd use with specmimeasures Of irrigation andor drainagePotential land use withoutspecial measures ofirrigation and or droinoaeOriginal so11 typeSoil suitability classification gives the alternative possibilities and potentialities of thesoils without giving a conclusion as to the best way of using them. This is determined bythe advisory classification and the administrative classification or sometimes by also usingdata of economic land use classification. These three are out with the scope of soil surveyinterpretation, although they are part of land classification. The soil surveyor sometimeshas some function in advisory classification, but he should be very careful in this respect.The best use of the soil is not only a question of the soil itself, but of various social, politicaland economic considerations. Sometimes even religious considerations come to thefore, such as the possibility of keeping pigs in predominantly Islamic countries. The soilsurveyor must concern himself with soil suitability classification, but he should be verycareful not to set himself on the chair of the administrator.Soil suitability classification is based on various assumptions and is never an absolutesuitability. It is always considered under certain circumstances, but this is not always48
ctInterpretation of soil surveyssufficiently realized, even by those people who are working largely with this kind ofclassification. An example of this are the famous 8 classes of the U.S. Soil ConservationService. Until 1957 these classes were used without any official indication as to the assumptionson which they were based, and it was only around that time that they werepublished (KLINGEBIEL, 1958). Sometimes soil suitability classifications are made by soilsurveyors without their consulting anybody else. If the soil surveyor is himself a goodagronomist, and if no possibility of consulting other people exists, he must sometimesdo this as a first approximation. It is our experience that often this way of putting thequestion is the best way of entering into an effective discussion with other specialistsconcerned. But anyhow the soil surveyor must realize that it is also partly the farm economist,the agricultural engineer, the crop specialist and the soil fertility expert who areconcerned with suitability and who have a say in this matter. Therefore the soil suitabilityresearch, and also the putting into practice of this kind of work, must be organizedas soon as possible in teams of about 4 or 5 people, but I would never advise anybody tomake a team larger than 5 people.The soil surveyor must take the lead because he is the man who can handle his soil unitsas individuals and who also knows their variability. The other reason for which the soilsurveyor must take a large part of this soil suitability work is the immense profit he himselfgains from this, because he keeps in contact with the practical importance of a soilscience and the needs of those people who are using the soil surveys. In this way his questionsand his basic research are directed to the fundamental problems that have relationto reality. Some may think this a degradation of fundamental research but I feel that themain reason for the enormous amount of research in a science like physics is not first ofall a question of the advancement of pure science.The suitability of a soil for a crop is determined by the following 5 factors:1. gross yield in pounds per acre,2. cost of production of this yield in man hours, pounds of fertilizers, machinery, etc.,3. the yield hazard, caused by the sensitivity of a crop on a certain soil to the less favourableinfluences of climate and man,4. the quality of the product,5. the soil pattern.The scope of this paper does not permit us to give a full description of these factors. Werefer to previous publications (VINK, 1956, 1958, 1960).The quantitative working of the above factors is determined by the general economic circumstances,technical advance, and management level. The management level is verywell described in the Soil Survey Manual (Soil Survey Staff, 1951) and by KELLOGG (1950).The definition of economic and technical level should in general be done in co-operationwith specialists on these fields.49
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Page 6 and 7: APPENDIXAERIAL PHOTOGRAPHY FOR SOIL
Page 8 and 9: LITERATUREBURINGH, P., 1960: Soils
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