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G e o d e r m a - E l s e v i e r P u b l is h in g C o m p a n y, A m s t e r d a m

Pr in ted in The Ne the r lands

S O I L G E N E S I S, S O I L C L A S S I F I C A T I O N A N D S O I L S U R V E Y

J. SCHELLING

Div is ion o f So i l Re sea r ch , So i l Survey Ins t i tu te , Wagen ingen The Ne the r lands )

Rece ived December 12 , 1969)

SUMM RY

M u t u al r e l a t i o n s h ip s e x i s t b e t w e e n s o i l g e n e s i s , s o i l c l a s s i f i c a t i o n a n d

s o i l s u r v e y . T h e f i r s t tw o s u b j e c t s a r e d e a l t w i th s e p a r a t e l y .

S o m e o f t h e g e n e r a l l i n e s i n s o il g e n e t i c i n v e s t i g a t i o n a r e t r a c e d .

N e x t t r e n d s i n s o i l c l a s s i f i c a t i o n a r e d e a l t w i th , T h e c o n c e p t s o f K n o x

1 9 65 ), w i t h s o m e a d d it i o n s , f o r m t h e t e r m i n o l o g y o f t h e p a p e r .

S o il c l a s s if i c a t i o n s y s t e m s a r e v a l i d w it h in c e r t a i n b o u n d a r y c o n d i -

t i o n s . W i t h m a n y of t h e e x i s t i n g s y s t e m s , l i t t l e a t t e n t i o n i s g i v e n t o t h i s ,

a l t h o u g h i t i s e s s e n t i a l f o r j u d g in g an d c o m p a r i n g . T h e m e t h o d f o l l o w e d

i n c o m p i l in g t r a d i t i o n a l c l a s s i f i c a t io n s y s t e m s i s b a s e d o n t r i a l a n d e r r o r .

B y s a m p l i n g o f t h e u n i v e r s e a c c o r d i n g t o t h e m e t h o d o f s t r a t i f i e d s a m p l i n g

o f s o i l - ) l a n d s c a p e b o d i e s , a s y s t e m s u i t a b l e t o s o i l s u r v e y c a n b e c o m p i l e d

m o r e q u i ck l y th a n b y t he m e t h o d o f s i m p l e r a n d o m s a m p l i n g . T h e s y s t e m

s h o u l d b e t e s t e d o n t h e o b j e c t i v e a n d b y a p p l i c a t i o n i n s o i l s u r v e y .

T h e d e v e l o p m e n t o f a s y s t e m i s v e r y c o m p l e x a n d u s u a l ly t a k e s o n

a n i t e r a t i v e c h a r a c t e r . T h e l o w e r a n d h i g h e r l e v e l s c a n be d e v e lo p e d

s e p a r a t e l y , b u t u n d e r a c o n ti n ua l i n t e r p l a y . T h i s i n t e r p l a y a l s o e x i s t s w i t h

s o i l s c i e n t i f i c k n o w l e d g e .

T h e l a c k o f s h a r p l y d e f i n e d a n d r e p r o d u c i b l e m e t h o d s i s s t ri k i n g . T h e

b r o a d l y d e s c r i b e d n u m e r i c a l t a x o n o m y i s a r e p r o d u c i b l e m e t h o d f o r p a r t s

o f t h e p r o c e s s . H o w e v e r , t h i s m e t h o d h a s n o t y e t b e e n s u f f i c i e n t ly t e s t e d .

I n s p i t e o f t h e p r e c i s i o n o f n u m e r i c a l t a x o n o m y , a g r e a t m a n y s u b j e c t i v e

c h o i c e s h a v e t o b e m a d e . O n l y w i t h in t h e f r a m e w o r k o f t h e s e c h o i c e s i s t h i s

m e t h o d r e p r o d u c i b l e .

A t t h e c o n c l u s i o n o f t h e a r t i c l e , t h e c o n n e c t i o n b e t w e e n s o i l g e n e s i s ,

s o i l c l a s s i f i c a t io n a n d so i l s u r v e y i s r e p r e s e n t e d i n a s y s t e m o f p r o p o s i t i o n s

a n d c o n c l u s i o n s . T h e s e c o v e r : 1 ) t h e c o n n e c t i o n b e t w e e n p e r m a n e n t s o i l

c h a r a c t e r i s t i c s , s t a te f a c t o r s o f s o i l f o r m a t i o n a n d g e n et ic p r o c e s s e s ;

2 )

t h e e x i s t e n c e of s o i l - l a n d s c a p e b o d i e s ; 3 ) t h e f o r m i n g o f a c l a s s i f i c a -

t io n s y s t e m f r o m a c o m p r o m i s e b e t w e e n t h e o p t i m i z i n g of c l a s s e s o f p e d o n s ,

o f s o i l - l a n d s c a p e b o d i e s a n d of c l a s s e s d i r e c t e d t o w a r d s a p p l ic a t io n ; a n d

4 ) t h e r e c o g n i t i o n o f d e l i n e a t e d s o i l b o d i e s o n t h e b a s i s o f s o i l o b s e r v a -

t i o n s , l a n d s c a p e o b s e r v a t i o n s a n d t h e r e l e v a n t t h e o r y .

I n t h e d i s c u s s i o n , s o m e i d e a s b a s e d o n t h e r e l a t i o n s o u t l in e d a r e

g i v e n o n s o i l r e s e a r c h w h i ch i s i m p o r t a n t t o s o i l s u r v e y .

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INTRODUCTION

It is undeniable that a soil map, the metho d used for its surv ey, the

map legend used in its construction, the system of soil classification being

followecl, and the curr ent un der sta nai ng of soil genesis a re i nter rela ted . In

soil science literature there are only a few publications in which these

subjects are dealt with in their relationship to one another, though separate

treatme nts of the subjects are certain ly found.

In vario us Soil Survey Manuals U.S.D.A., New Zealand, B und esr epu -

blik Deutschland etc.) the practical aspects of soil classification and soil

survey are dealt with. A more fundamental approach towards the questions

surrounding classification and survey ing is often lacking. The relationship

to the genesis is usually approached by way of the state factors of soil

formation.

Books devoted to a single soil classification system largely confine

themselves to a description of the system as such. The aim is often indi-

cated only brief ly and inco mpl etel y De Bakker, 1970). In most ca ses the

method that has been followed in compiling the system scarcely comes up

for discussion. Textbooks on soils often devote little attention to questions

surrounding soil survey. They usually do indicate the connection between

soil classification and genesis.

In a large number of articles concerned with soil classification and

soil survey, many aspects are touched upon, which will also be discussed

in this article. These publicatio ns lack, howev er, a considerati on of the

relationship with the genesis of the soils.

In this arti cle, these pr obl ems will be approached as follows: After

a brief review of some general ideas about soil genesis, the development

of systems of soil classification for soil survey purposes will be discussed.

Alongside tradit ional me thods, num eri cal methods will be examined. In

the final part of this a rti cle , an attempt will be made to indicate in a sy st em

of propositions and conclusions, the mutual relationships between soil

genesis, soil classification and soil survey. This will be based on perma-

nent soil characteristics. Finally, in the discussion, the general trends of

investigation which are of importance to soil survey will be given.

S O I L G E N E S I S

W i t h o u t t r y i n g t o a c h i e v e p e r f e c t i o n a n d o m i t t i n g h i st o r ic a l d e v e l o p -

m e n t , s o m e t r e n d s i n t h e i d e a s a b o u t s o i l g e n e s i s w i l l b e g i ve n .

tate factors of soil format ion

F a c t o r s d e t e r m i n i n g t h e co n di t i on s u n d e r w h i c h s o il f o r m a t i o n t a k es

p l a c e h a v e a l w a y s b e e n o f i n te r es t . R u s s i a n p e d o l o gi s t s d e v e l o p e d t h e

t h e o r y o f f a c t o r s o f s o i l f o r m a t i o n : c l i m a te , o r g a n i s m s , t o p o g r a p h y ,

p a r e n t- m a t e r ia l n d t i m e. J e n n y ( 1 9 4 1 , 1 9 6 1 ) x p a n d e d t h is t h e o r y a n d a t t e m p t e d

to give quantitative expr es si on to the individual factors. He rightly

c h a n g e d t h e t e r m f a c t o rs o f s o i l f o r m a t i o n i n t o s t at e f ac t or s , w h i c h

s h o w s t h a t h e r e t h e e x t e r na l c o n d i t i o n s a r e i nd i ca t ed . S t e p h e n s ( 19 4 7) h a s

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provided a further specification, without deviating from the general outline

given by Jenny. Their line of thought has led to an improvement in insight,

but unfortunately, it has not developed greatly. Butler (1964) points this out.

If a satisfactory model for quantitative use had come into existence,

this could have prevented many discussions on the question of which

factors are the most important.

The possibilities of making worthwhile investigations into the rela-

tionship of soil to state factors differ strongly from case to case. Some

factors can be measured exactly, while for others, we must make do with

extremely speculative estimations, as they belong so far back in time that

no reliable information concerning them can be obtained. But such difficul-

ties a re i nherent to the subject, and although they can be avoided as far as

possible, this does not solve the problem.

One of the difficulties which crop up in the study of state factors is

caused by the interaction of state factors among themselves and because,

for instance, the parent - mat eri al is both state facto r and part of the soil.

For this reason the need arises for an improvement and a refining of the

theory. The systems theory offers a means towards this end.

Closed and open systems

The simplest system is a closed system, over whose bor der s no

material or energy is either added or lost.

In many quantitative investigations on soil genesis, single soil

profiles are studied as though they were cl osed syst ems. This assumpti on

is usually not quite true, and the scope of the model is somewhat too

limited.

In Russian literature, with which, I am, unfortunately not sufficiently

familiar, there are valuable ideas to be found, including those of Parfenova

(1963), Kovda et al. (1968) and others.

The. concept of the geo che mis try of landscap es (Polynov, in

Parfenova, 1963) opens up perspectives for the consideration of the mutual

relationships of various soils which are found together in a landscape.

Approaching a lands cape as a closed syste m is, however, not altogeth er co r-

rect. Ehwald (1960) demonstrates that the soil system can be described

with the theory of open systems by von Bertalanffy (1950). I do not know of

any further elaboration on this concept.

In geology, matters are further advanced with regard to the applica-

tion of the systems theory (Chorley, 1962; Ruhe and Walker, 1968).

Model o soil genesis

In the concept of state fact ors , as found in litera ture, a dire ct r elation

is postulated between state factors and the soil. It is preferable, however,

to use the following model:

input black box soil

s ta te factors ,e . . . . I soil forming pro cess es I ~ . . . .

output

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In this model, emphasis is laid on the fact that the state factors actuate the

commencement of certa in processes, but that these processes form the

essent ial link in the genesi s of the soil. In a study of this sy st em,

considerati on should be given to the parts separ ately , as well as to their

mutual relationships.

The relation between state factors and the soil (without the connecting

link) has already been mentioned above.

The study of the soil-forming processes themselves is one of the most

important subjects of experiment al pedology (Hallsworth and Crawford,

1965). In this, there is a certain risk of systems being studied which do not

correspond with conditions in the field. In this respect, all kinds of percola-

tion experiments are carried out in tubes with undisturbed soil, whereby

the moistur e tension at the bottom of the column is unnatural. Moreov er,

the effects of alternative evaporation of soil moisture, drying and remoist-

ening, are not built into the model. The results cannot then simply be

applied in the field.

The comparative study of soil profiles, which have been developed

under well-defined circumstances, can also supply important contributions.

If we revi ewth e lit erat ure on certain soils, it will be clea r that the

existing material is often fragmentary and the hypotheses have not always

led to a coherent theory.

From this brief ~eview of soil genesis, it would appear that there is a

need for further investigation into the contents of the black box, and for a

furth er elaboration of lar ger models, such as landscapes, with the system s

theory.

TRENDS INSOIL CL SSIFIC TION

The concepts of Knox

Soil classification is a static arrangement of soils. The characteristics

of the soil are the result of dynamic processes; what we classify are

merely momentary glimpses. This contradistinction will be gone into

further in a following section. For the moment it is sufficient to establish

that the line to be followed in this section is that of a static situation.

K n o x ( 1 9 65 ) fo r m u l a t e d a n e x c e ll e n t s e r i e s o f c o n c e p t s ,

la ter

e l a b o r a t e d b y V a n W a m b e k e ( 1 96 6 ), w h i c h m a k e it p o s s i b l e t o d e s c r i b e t h e

s o i l a s a t h r e e - d i m e n s i o n a l e n t it y in r e la t i o n w i th th e s o i l c l a s s i f i c a t i o n

and the

s o i l m a p . A s t h e s e c o n c e p t s w i l l b e u s e d t h r o u g h o u t

this article,

they will be summarized here briefly.

General concepts

Definitions of terms u s e d :

Individual the smallest natural body that can be

d e f i n e d a s

a thing

c o m p l e t e i n i t s e l f . I n d i v i d u a l s th a t a r e o f i n t e r e s t in c l a s s i f i c a t i o n are

m e m b e r s o f a c la s s .

A class is an abstract field, formed by the concept of that class

( F i g . l A ) . T h i s c o n c e p t i s d e f i n e d w i t h t h e a i d o f

charac te r is t ics (s ingula r

or more complex), which

f o r m t h e b a s i s f o r m e m b e r s h i p

of the class.

This view does not conform with that of th~

c l a s s b e i n g an a g g r e g a t e

of

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2

l

p = u n i v e r s e p = u n i v e r s e

s = c l a s s x = m e m b e r

b o u n d a r y o f s T = c l a s s a s a g g r e g a t e o f m e m b e r s

- - - b o u n d a r y o f T

b o u n d a r y o f s

Fig.1. Ideas oh the concept of c lass . A. The c las s as an abstra ct f ie ld,

formed by the concept of that class. B. The class as an aggregate of i ts

me mbe rs .

i ts memb er s Fig. lB). In the la t ter case , one must be able to dis t inguis h

individual mem ber s, and these together then form the c lass .

A u n i v e r s e

is a superclass that contains a l l the objects and includes

al l the other c lasses under considerat ion. This can be, for instance, a

certa in a re a for which a c lassi f ica t ion is drawn up, but i t may also be a

certa in abstract ion, e .g. , a soi l development cycle .

A part i cula te universe contains dis cr e t e objects that can be counted.

The pa rt s which belong to a continuous un iv er se cannot be counted.

For a quant i ta t ive t reat ment , such a uni ver se must be divided into ar bi t r ar y

uni ts of measurement .

The concept of univ erse is of great i mpo rta nce bec ause a law, a

theory or a c lass i f ica t ion appl icable to a ce r ta in u nivers e need not the re fore

nec es sar i ly apply to other uni ver ses . By defining the boundary condit ions we

de l inea te the border s of the universe .

A m e m b e r - b o d y is a body in a physical universe that qual i f ies for

member ship in a class . In a pa r t ic u la te unive rse , the member -bo dies and

the individuals are ident ical . In a cont inuous univer se , the me mb er -b od ies

are arbi t rary. The one body does not exclude the other and their number

there for e i s inf in i te . The la r ges t d imens ions of these a rb i t r a ry memb er-b odie s

a re de t e rmine dby the c l a s s - l imi t s . The min imum d ime ns ions a re de t e rmine d

opera t iona l ly through the fac t tha t a l l the pro per t ie s and chara c te r i s t ic s

requi r ed for member ship of the c lass , must be mea sur able wi thin the

me mbe r -body .

A n a t u r a l i n d i v i d u a l is an individual that is dis cr e te and independent

of the obser ver . That is to say, i t is a mem ber -b od y within a part icul a te

universe .

An a r t i f i c i a l i n d i v id u a l is a human construct within a continuous

universe . I t i s c rea ted a rb i t ra r i ly , for convenience .

The above can be reduced to the fol lowing thr ee pri nci ples :

1) Classes are abstract f ie lds which fa l l within the concept of the

class, and need not be groups of individuals.

2) In pa r t icu la te unive rses , na tura l indiv idua ls cons t i tu te the mem-

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bership of classes. In continuous uni ver ses there are no individuals, except

the arbitrarily formed artificial individuals.

3) Artificial individuals are mem be r-b od ie s of minimum size dete r-

mined operationally).

Soil bodies

number of soil bodies, significant for our problem, will be examined

here.

2

G

i

i

Fig.2. The pedon.

Pedon The pedon Fig.2) is an artifi cial individual of arb it rar y size. This

is determined by the lateral variations in soil characteristics which are

used for the classification. The slope is thus excluded, because for this,

s t i l l larger bodies are required for a re liable measurement. Pedons are

not mutually exclusive and may overlap one another. Accordingly, they

are infinite in number. For a fur ther descrip tion of the pedon, refer enc e

is made to Soil Surv ey Staff 1960), Simons on and Gardi ner 1960),

John son 1963) and Arno ld 1964, 1966).

Soil landscape units A soil landscape unit is an objective, not arbitrary,

geogr aphica l body of soil. It is a spatial aggr ega te of pedons. It s thicknes s

is that of the pedon. The lat era l boun dari es a re deter mined by the

geographic pattern of change in soil ch ara cte ri sti cs according to objective

boundar y crit eri a. Within the mean ing of Knox, the soil landscape units

cannot consequently have arbitrary boundaries. That is to say, an arbitrary

choice of the boundary criteria can be made beforehand, but with reference

to the crit erion chosen, the late ral bounda ries ar e fixed by the ch ar act er is -

tics of the soil as it is found there . With each cri teri on, the soil landscape

units are mutually exclusive.

For the following discussion, we make a further distinction between

soil landscape bodies, polypedons and landscape bodies.

A soil landscape body Fig.3) is a soil landscape unit for which the

maximum lateral rate of change of soil characteristics is used as the

boundary criterion.

A polypedon Fig.4) is a soil landscape unit, for which the boundary

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4

_ d l

Fig.6. The delineated soil body (after Simonson, 1964; 196~.

In Si s paper, such compound map units as complexes, undifferentiated

units etc. will not be gone into, as their origin is connected with the scale

of the map and does not rest on considerations of principle.

With the concepts given above, the relationship between soil genesis,

soil classification and soil survey can be described. At the outset, a confu-

sion of concept s frequ ent ly met with should be point edout : that between

soil classification and map legend.

o i l c la s s i f ic a t i o n a n d m a p l e g en d

In general, the terminology of the soil classification system is used

without further ado for map legends. E.g., in the U.S.A. Soil classification

sys tem (Soil Surv ey Staff, 1960) the te rm soi l se ri es has a manifold

meaning, that is only par tly rec og niz ed the re (p.174). It is used: (1) to denote

a taxonomic class; (2) to denote a pedon that satisfies certain class

crit eria ; (3) to denote a polypedon that satis fies certain class crit eria;

(4) to denote a certain delineated soil body of a soil map, consequently

incorporating inclusions of unlike pedons; and (5) to denote a certain unit

of the map legend, a class of delineated soil bodies.

Especiall y becau se of the fact that the last two kinds are not separated

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from the others , th ere is a great r isk of confusion. The dist inct ion between

taxonomic uni ts and mapping uni ts is se t out mo re c l ear ly in the Soil Survey

Manual.

In The Netherlands (Steur, 1964) and later in the Deutsche Demokra-

tische Republik (Ehwald et al . , 1966; Haase, 1968), a separation is made

between soi l c lassi f icat ion and map legend. Soil c lass if i cat i on covers a

universe of pedons and polypedons, while map legends cover a universe of

the delineated soil bodies of a soil map. Not only is this more correct in

principle , but i t a lso provides the pract ical map user with a more correct

rep rese nta t ion of affa irs , as the existence of inclus ions is c lear ly indicated.

e n e r a l b o u n d a ry c o n d it io n s a n d p r o c e d u r e s f o r c o m p i l i n g s o i l

c l a s s i f i c a t i o n s y s t e m s

In this sect ion, methods for compi l ing soi l c lass if i cat i on sys tem s

for use in soil surve.y will be disc uss ed. A questio n could be ra is ed about

constr uct ing soi l c lassif icat ion sy st ems that are not sui table for soi l survey.

This quest ion fa l ls outside the frame-work of this art ic le . Also the funda-

mental principles of c lassif icat ion, which have been discussed a t length

elsewhere (Cline, 1949; Williams and Dale, 1965) will not be repeated here.

In compil ing any soi l c lassif i cat io n syst em, ther e are a number of

elem ent ary condi t ions that must be sa t isfied. These condi t ions wil l be

sum mar ized br ie f ly , and deal t wi th in more de ta i l a f t e rwards :

(1) A purpose is chosen for the c l assi f ica t ion system.

(2) A definition is given of what is meant by soil.

(3) The syste m is compiled for a certa in defined univ erse of soi ls .

(4) In compil ing a soi l c lass if ic at io n sys tem f or use in soi l sur vey,

a defini t ion is given of what is meant by permanent soi l characteris t ics

and by var iable so i l charac te r i s t ic s .

(5) Representat ive se ts of samples of each c lass to be formed are

col lec ted for process ing .

In this context, sam pl e mean s a number of soi ls which ar e chosen

as being representa t ive of the universe . These may be actual soi l profi les ,

pedons or other bodies, or abstract ions, such as centra l concepts or modal

prof i le s .

(6) The cha ra ct er is t i cs of the soi l s chosen for the compila t io n of the

clas sif icat ion syste m must contain suffic ient ly compl ete inf ormation 1,

regardi ng the common ch ara c te r i s t ic s which typify the c lasses .

The i tems mentioned under 5 and 6 are less boundary condit ions for

the sy ste m i tse lf , than for the compila t ion of the sy stem . The boundary

conditions are dealt with in the following section.

P u r p o s e

The soi l c lass i f ica t ion sys tems d iscussed here a re in tended for use

in soi l survey. These surveys may be directed towards a broad fie ld of

appl ica t ions , f rom agr icul ture and town-and-count ry p lanning to c iv i l

engineer ing and mi l i t a ry purposes . Or the re may be spec i f ied a more

lInformation is used here in the meaning employed in information theory (Shannon

and Weaver, 1963).

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r e s t r i c t e d a n d a m o r e p r e c i s e f i e l d of a p p l i c a t i o n . I n e s t a b l i s h i n g t h i s o b -

j e c t i v e , t h e m a t e r i a l f a c i l i t i e s a v a i l a b l e m u s t b e t a k e n in t o a c c o u n t t e c h -

n i c a l e q u i p m e n t , m a n - p o w e r , t i m e , m e t h o d o f s o i I s u r v e y ) an d a l s o th e

n a t u r e o f t h o s e w ho w i l l b e u s i n g t h e s y s t e m . A v e r y a d v a n c e d s y s t e m , f o r

i n s t a n c e , w i l l n o t b e p u t t o u s e s u c c e s s f u l l y b y i n a d e q u a t e l y e d u c a t e d

p e r s o n n e l .

efinition of soil

W i t h in th e f r a m e - w o r k o f t h e g i v e n o b j e c t i v e , a d e f i n i t i o n o f s o i l

s h o u l d b e s t a t e d e x p l i c i t l y a s a b a s i s f o r t h e s o i l c l a s s i f i c a t i o n s y s t e m . T h i s

d e f i n i t i o n i s c l o s e l y r e l a t e d t o t h e d e s i r e d a p p l i c a t i o n s . F o r c i v i l e n g i n -

n e e r i n g r o a d - m a k i n g , h o u s e - b u i l d i n g e t c . ) , i t m a y b e d i f f e r e n t f r o m t h a t

r e q u i r e d f o r p u r e l y a g r i c u l t u r a l p u r p o s e s . I t c o n c e r n s a b o u n d a r y i n b o t h

a h o r i z o n t a l d i r e c t i o n , b e t w e e n s o i l a n d n o t - s o i l , a s w e l l a s i n a v e r t i c a l

d i r e c t i o n t he t h i c k n e s s o r d e p t h of t h e p e do n ) .

efinition of the universe

I n d e f i n in g t he u n i v e r s e f o r a s y s t e m i n t e n d e d f o r s o i l s u r v e y , t h e m o s t

o b v i o u s t h in g w o u l d b e t o u s e a g e o g r a p h i c a l b o u n d a r y , e .g . a c o u n t r y , a

c e r t a i n c o n t in e n t , th e w h o l e w o r l d . E v e n w h e n t h e a r e a i s l i m i t e d , t h e

c o m p i l a t i o n i s c a r r i e d o u t w i t h a l i m i t e d c h o i c e o f s o i l s , a s a m p l e f r o m a

m u c h g r e a t e r u n i v e r s e . T h i s s a m p l e - f o r t h a t p a r t i c u l a r s t a g e o f t h e

p r o c e e d i n g s f o r w h i ch i t h a s b e e n c h o s e n - f o r m s t h e u n i v e r s e i n a m o r e

r e s t r i c t e d s e n s e .

Permanent soil characteristics

F o r p r a c t i c a l r e a s o n s , o n ly t h o s e c l a s s i f i c a t i o n s t h a t a r e b a s e d o n

p e r m a n e n t s o i l c h a r a c t e r i s t i c s a r e a p p l i e d i n s o i l s u r v e y . F o r t h e u n i v e r s e

t o b e d e s c r i b e d , a n a r b i t r a r y s e p a r a t i o n i s t h e r e f o r e m a d e b e tw e e n p e r -

m a n e n t a nd v a r i a b l e s o i l c h a r a c t e r i s t i c s . T h i s b o r d e r l i n e i s , b y t h e n a t u r e

o f t h i n g s , b o u n d u p w i th t h e o b j e c t i v e o f s o i l c l a s s i f i c a t i o n a n d s o i l s u r v e y .

B y p e r m a n e n t c h a r a c t e r i s t i c s w e m e a n t h o s e s o i l c h a r a c t e r i s t i c s ,

w h i c h o v e r l o n g e r p e r i o d s t e n s ) of y e a r s ) r e m a i n p r a c t i c a l l y th e s a m e ,

o r t h o s e w h i c h h a v e a c o n s t a n t c y c l i c c h a r a c t e r e . g . s e a s o n a l v a r i a t i o n s

w i t h a n a m p l i t u d e th a t r e m a i n s u n i f o r m ) . B y v a r i a b l e s o i l c h a r a c t e r i s t i c s

w e m e a n t h e c h a r a c t e r i s t i c s w h i c h c h a n g e a t s h o r t i n t e r v a l s o n e o r s e v e r a l

s e a s o n s o r y e a r s ) .

T h e e x t e n t o f t h e c h a n g e s a d m i t t e d i s r e l a t e d t o t h e o b j e c t i v e a n d to

t h e w h o l e c o m p l e x o f f i n a n c i a l , m a t e r i a l a n d m e n t a l f a c i l i t i e s w h i c h f o r m t h e

f r a m e - w o r k w i t h i n w h i c h t h e c l a s s i f i c a t i o n m u s t b e p u t t o u s e . T h u s i n

T h e N e t h e r l a n d s , a n u m b e r o f a s p e c t s o f c h e m i c a l s o i l f e r t i l i t y a n d of s o i l

s t r u c t u r e , w h i c h a r e b o u n d up w i t h s o i l m a n a g e m e n t , a n d w h i c h c a n v a r y

f r o m p a r c e l t o p a r c e l , m u s t b e c o n s i d e r e d t o b e a m o n g t he v a r i a b l e s o i l

c h a r a c t e r i s t i c s .

A n e x a m p l e t a k e n f r o m t h e A m e r i c a n s o i l c l a s s i f i c a t i o n i s t h e 9 t h a s -

s u m p t i o n S o i l S u r v e y S t a f f, 1 9 60 , p . l l ) , w h i c h s t a t e s t h a t it i s u n d e s i r a b l e

t o h a v e a c h a n g e i n th e c l a s s i f i c a t i o n o f a s o i l a s a r e s u l t o f a f i r e o r a

s i n g l e p l o w i n g .

1 74 G e o d e r m a , 4 1 97 0)

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Representative sample sets of soils

For the boundary conditions which apply for the compilation of the

system, i t is obvious that a re la t ionship should exist between the sample se t

of soi ls and the c l ass es that wil l f inal ly be formed. With the f i r s t sam ple s

taken, the choice will often not yet be suf ficien tly adapted, as the c la ss es

to be formed ar e not yet known. Compil ing a soi l c lassif icat ion syst em wil l

accordingly acqui re an i t e ra t iv e charac t e r . Pra c t ic a l cons idera t ions , such

as a minimum are a covered by the s oi ls c oncern ed within the geographic

universe , and the frequency of occurrence of certa in soi ls , play their part

in es tabl i sh ing c r i te r ia for sampl ing .

The characteristics chosen contain sufficient information

In compil ing a c lass if ica t ion syste m, i t is i mpos sibl e to use a l l the

ava i lable charac t e r i s t i c s . Fo r pr ac t i ca l reas ons a l imi ted number of

char ac te r i s t i c s wi ll have to be se lec ted . These c hara c te r i s t i c s must con-

ta in the information essent ia l to enable both the s im il ari t ie s and the diff er-

ences of the c las ses that wil l be for med, to be indicated effect ively.

With these general boundary condit ions taken into account , some l ines

to be followed in construct ing a s ys te m of soil clas sif icat ion can now be

given.

In the f i rs t place the above- menti oned boundary condit ions wil l have

to be defined. Then a certa i n method wil l be s e lect ed for the construct io n

of the system. With the means se lec ted, a prim ar y approximation of the

system can now be made.

This sy s tem i s a t tuned to the sample se t s and chara c te r i s t ic s se lec ted .

Its val idi ty for the e nt i re u niv ers e to which i t wil l be appl ied is not yet

es tabl i shed, nor i s i t s prop r ie ty in re la t ion to the object ive. The c las s i f ica -

t ion has more or less the character of a hypothesis that s t i l l has to be

tested. The resul t s of this test ing can lead to an adjustment of the syste m.

Since we want to produce soi l m aps with the c lassif icat ion, an i m-

portant part of this test ing is to judge i ts usefulness in producing soi l maps.

It is obvious that both in the objective and the testing, a relationship must

exist with the method of soil survey used.

The procedure followed in compiling traditional general soil

classification systems

eneral

By t radi t iona l genera l so i l c lass i f ica t ion sy s tems, we mean a l l those

sys tem s which, by a pr oce ss of t r i a l and erro r, were made as sui table as

poss ible for a certa i n uni vers e of soi ls . The great majo ri ty of exist ing

c lass i f ica t ion sys te ms be long to th i s group.

There i s a t endency to base the sy s tem s on measurab le so i l chara c te r -

is t ics , as is done in the Ameri can, Dutch and in Ehwald s sys tems. In this

way an a t tempt is being made to redu ce the subject ive e lement in the use of

the system as much as possible . I t was not only the desire for accuracy of

formulat i ng, fro m a sc ient i f ic point of view, that led to this proce dure , but

i t was a lso due to the wishes expressed by those using soft maps for

technical applications. It is to be expected that as the knowledge of soil

char ac te r i s t ic s inc r eases , the de f in i t ions of the uni t s wi l l be grea t ly im-

proved upon.

Geoderma, 4 (1970) 175

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I n o r d e r t o m a k e c l e a r t h e p r o c e d u r e f o l l o w e d i n p r a c t i c e , a f e w

h y p o t h e t i c a l an d s t r o n g l y s i m p l i f i e d a p p r o x i m a t i o n s w i l l b e d i s c u s s e d i n

t h e n e x t s u b - s e c t i o n . F o l l o w i n g t h a t , a d e s c r i p t i o n w i l l b e g i v e n o f a m o r e

c o m p l i c a t e d p r o c e d u r e , m o r e i n c o n f o r m i t y w i th r e a l i t y .

Two idealized strongly simplified approximations

A s s u m e t h a t o n l y t h e d i s c r e t e c h a r a c t e r i s t i c s o f a c e r t a i n u n i v e r s e a r e

k n o w n , w h i l e no t h in g i s k n o w n o f t h e i n t e r r e l a t i o n s h i p s b e t w e e n t h e s e

c h a r a c t e r i s t i c s a n d o f t h e g e n e s i s . V a r i o u s a v e n u e s a r e n ow op e n , i n c l u d i n g

t h e f o l l o w i n g :

Simple random sampling. T h e b o u n d a r y c o n d i t i o n s a r e e s t a b l i s h e d . I n t h e

u n i v e r s e s e l e c t e d , e . g . a g e o g r a p h i c a l a r e a , a n u m b e r o f s o i l s a r e c h o s e n

a t r a n d o m ( s e e F i g . 7 ) . C h a r a c t e r i s t i c s a r e s e l e c t e d t o t y p i f y t h e s o i l s a n d

t h e s e c h a r a c t e r i s t i c s a r e e s t a b l i s h e d . I n o n e w a y o r a n o t h e r , i t i s a s c e r -

t a i n e d w h i c h s o i l s r e s e m b l e o n e a n o t h e r .

C l u s t e r s o f s o i l s a r e d i s t i n g u i s h e d , a n d b e c a u s e a n i d e a i s f o r m e d o f

t h e c e n t r a l c o n c e p t s o f t h e s e c l u s t e r s a n d o n e c a n b e c o m p a r e d w i t h

a n o t h e r , a p r i m a r y a p p r o x i m a t i o n o f a c l a s s i f i c a t i o n c o m e s i n t o b e i n g . A

n u m b e r o f s o i l s w h i c h o c c u r i n f r e q u e n t l y , a n d do no t b e l o n g t o a ny o f t h e s e

c l u s t e r s , w i l l b e n e g l e c t e d i n f u r t h e r o p e r a t i o n s . T h e e x t e n t o f t h e f i r s t

s a m p l i n g a n d t h e q u a l i t y o f t h e c l a s s i f i c a t i o n o b t a i n e d w i l l d e t e r m i n e

w h e t h e r t h e r a n d o m s a m p l i n g a n d t h e w h o l e o p e r a t i o n w i l l h a v e to b e r e -

p e a t e d w i t h a l a r g e r n u m b e r o f s a m p l e s , o n c e o r e v e n m o r e t i m e s .

N e x t th e c l a s s i f i c a t i o n o b t a i n e d i s t e s t e d i n d e t a i l e d s u r v e y i n g t o

a s c e r t a i n w h e t h e r d e l i n e a t e d s o i l b o d i e s o f a s u f f i c ie n t l y h o m o g e n e o u s c o m -

p o s i t i o n a r e t h u s o b t a i n e d . A t t h e s a m e t i m e , t e s t s w i l l h a v e t o b e m a d e o f

t h e p r o p r i e t y i n r e l a t i o n t o t h e o b j e c t i v e . O n t he b a s i s o f t h e i n s i g h t s t h u s

a c q u i r e d , t h e c l a s s i f i c a t i o n i s a d j u s t e d . I t i s o b v i o u s f r o m t h i s a c a d e m i c

e x a m p l e th a t w i t h r a n d o m s a m p l i n g a s t he f i r s t s t e p , a s u b s e q u e n t i n t e n s i v e

t e s t i n g o f t h e m a p p a b i l i t y i s e s s e n t i a l .

Sampling of landscape bodies stratified sampling).Hagood a n d P r i c e ( 1 95 2 )

u s e t he t e r m s t r a t i f i e d s a m p l i n g i n c o n t r a d i s t i n c t i o n t o t h e t e r m s i m p l e

s a m p l i n g i n w h i c h o n e s a m p l e i s d r a w n f r o m t he w h o l e u n i v e r s e .

I n s t r a t i f i e d s a m p l i n g a g r o u p o f r a n d o m s a m p l e s i s s e l e c t e d , o n e

f r o m e a c h of t h e s e v e r a l p r e d e t e r m i n e d s t r a t a o r p a r t s o f t h e u n i v e r s e .

O f t h e s e v e r a l p o s s i b l e b a s e s f o r t h i s s t r a t i f i c a t i o n , p h y s i o g r a p h y i s

u s u a l l y p r e f e r r e d i n T h e N e t h e r l a n d s . I n t h e s e c o n d h y p o t h e t i c a l c a s e t h e

f o l l o w i n g m e t h o d i s u s e d ( F i g . 7 ) . A g e n e r a l p h y s i o g r a p h i c r e c o n n a i s s a n c e

i s m a d e o f t h e g e o g r a p h i c u n i v e r s e . L a n d s c a p e b o d i e s a r e d e l i n e a t e d in a

l i m i t e d n u m b e r , b a s e d o n p h y s i o g r a p h i c c r i t e r i a . N e x t a s e t o f s a m p l e

s o i l s i s c h o s e n i n su c h a w a y t h a t a l l d i f f e r e n t k i n d s o f l a n d s c a p e b o d i e s

a r e e a c h p r e s e n t w i t h th e s a m e n u m b e r o f s a m p l e s .

I n t h i s s a m p l e c l u s t e r s a r e m a d e o f s o i l s t h a t r e s e m b l e o n e a n o t h e r .

T h e f o l l o w i n g s t e p s a r e v e r y m u c h l i k e t h e h y p o t h e t i c a l c a s e m e n t i o n e d

u n d e r t h e s u b - s e c t i o n o n " S i m p l e r a n d o m s a m p l i n g " . I t i s , h o w e v e r , o b v i o u s

t h a t t h e s y s t e m w i l l n e e d f a r t e s s a d j u s t m e n t t o m a k e i t s u i t a b l e f o r s o i l

s u r v e y t h a n i n t h e p r e v i o u s c a s e .

T h e s e e x a m p l e s o n l y s e r v e t o s h ow t h a t w h i l e s i m p l e r a n d o m s a m p l i n g

i s c e r t a i n l y n o t s t a t i s t i c a l l y i n c o r r e c t , a s y s t e m s u i t e d t o s o i l s u r v e y c a n

1 76 G e o d e r m a , 4 ( 9 7 0 )

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be reached mor e quickly with a physiog raph ical ly guided st ra t i f ie d

sampling.

utline of the compilation of a traditional soil classifwatior~ system

Each scheme showing the way in which a t radi t ional c lassif icat ion

syst em is compiled must , of neces si ty , contain a number of s impli f icat io ns.

The actual procedure is so complex that only a broad outline can be given.

One possible method is set out in Fig.8 and 9.

To find out which points could be improved and how this might be

achieved with other methods, the exist ing method must f i rs t of a l l be more

clearly in mind. In a discussion based on the diagram, specia l a t tent ion

must be given to the following aspects:

(1) The whole procedure is exceedingly complex and comprises

numerous cases of feed back and mor e or l ess i ter a t iv e approach es.

(2) In the past (Manil, 1956) the idea has come up of approaching a

classi f icat io n from bot tom to top, or fro m top to bot tom ( ascendante e t

descendante ) , with somewhat disdainful comments concerning the f i rs t .

It will be obvious from the diagram that both are vital , but that for soil

survey the lowest level is of decisive importance.

(3) There should be a manifold testing of the system, that is to say, i t

should be tested on exist ing knowledge, on the sp ecific sui tabi l i t y for sur -

veying the geographic universe for which it has been set up, and on the

objective for which it has been compiled.

Fig.8 gives a general diagram. The method shown is based on sampling

from a certa in universe . The lower level s are appro ximat ed with one kind

of sampling, the higher levels with another. Both are placed in a mutual

rel ati ons hip and influence one another . At the same time, the re is a contin-

uous interaction with the total knowledge of soil science. Finally, as a

resul t of a l l these in te rac t ions , one in tegra t ed c lass i f ica t ion sys tem comes

into being. In the following pa ra gr ap hs this will be gone into in more

detail (Fig.9).

After the fixation of boundary conditions a sampling method is chosen

for the establ ishment of the lower level uni ts . A method as described in

the sub-sec t ion on Sampl ing of l andscape bodies i s pre f e rred : s t ra t i f ied

sampli ng of physiog raphic landscape bodies. This del ineat ion of landscape

bodies is part ly based on previous knowledge. The same is t rue for the

choice of l ayers , hor izons and charac te r i s t ic s . By compar i son of so i l s ,

formation of centra l concepts , weight ing of characteris t ics and c lustering,

an approximation of a sy stem is developed. By repet i t i on of these s t ages

the c lassif icat i on is gradu al ly adapted. Fi nal ly the sys tem is test ed by

detailed soil mapping and in relation to the applications, and then adapted

as far as is needed.

For the higher levels a sample is taken, based on pri or knowledge

and the res ul t s of the low level c lassif icat ion pro cedu re so far . The

pr oce du re is about the s ame as fo r the low level sam ple , but the connection

between high and low level c l assi f icat ion is a lso con sidered. After suf-

fic ient adaptat ion a f i r s t draft of an integr ated sys tem of higher and

lower levels is obta ined.

In the above, one vital part has not been taken into consideration: the

choice of pa r ame te r s of so i l char ac te r i s t ic s . Alongs ide a l l manner of

178 Geoderma, 4 (1970)

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higherevels

~ s i f i -unv e / ~ s e ~ n

\ J s Y s t l m

lowerevels

F i g .8 . G e n e r a l d i a g r a m o f t h e c o n s t r u c t i o n o f t r a d i t i o n a l s o i l

c l a s s i f i c a t i o n s y s t e r 0 s .

c h O ic e o f - d e s c r i p t i o n a n d ~ c o n c e p t i o n ,

s l m p l e s f o r m e a s u r e m e n t

h i g h e r

c h o i c e o f l a y e r s ,

h o r i z o n s ,

l e v e l s ~ l l c h a r a c t e r i s t i c s a n d

m e a s u r i n g m e t h o d s

] d e t e r m i n a t i o n k n O w l l K I g e f :

- r e l a t i o n s b e t w e e n s t a t e f a c t o r s a n d ,,

I o f b o u n d a r y - t h e o r y o f ' s o i l g e n e s i s

I c o n d i t i o n s - e x i s t i n g c l a s s i f i c a t i c m s y s t e m s

a p p l i c a t i o n s

l a y e r s ,

h o r i z o n s ,

c h a r a c t e r i s t i c s a n d d e s c r i p t i o n a n d

m e a s u r i n g m e t h o d s , ~ m e a s u r e m e n t

c h o i c e o f

s a m p l e s f o r

l o w e r l e v e l s - - o f u n i t s

g r o u p i n g e n d

, tng

l

of

Il f tcaUon

I m i n s o i l

~ i ng

and

c a t i o n s

Lation

t

r a t e d 1

m C a t'o o

a t i o n

of

s l f i c a t l o n

s m i n s o i l

~ l n g a n d

I c o t I o n s

t

, p i n g a n d

d e f i n i n g

F i g 9 D i a g r a m o f t h e c o n s t r u c t i o n o f s o i l c l a s s i f ic a t i o n s y s t e m s

G eod erm a, 4 1970) 179

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r e s t r i c t i o n s o n t h e t e c h n i c a l a n d m a t e r i a l f i n a n c i a l ) l e v e l , t h i s c h o i c e

w i l l l a r g e l y d e p e n d o n i n s i g h t s i n t o s o i l g e n e s i s a n d t h e s i g n i f i c a n c e o f t h e

p a r a m e t e r s f o r a p p l i c a t i o n . N o r m a l l y t h i s p a r t i s n o t t r e a t e d o b j e c t i v e l y

e i t h e r , b u t u n d e r g o e s a s t r o n g s u b j e c t i v e i n f l u e n c e .

Nurtleric t[ ta.vo~zo~71y

G e~ e r a l

A m o n g t h e d e m a n d s i m p o s e d o n s c i e n c e a r e a c c u r a c y a n d r e p r o d u c i b i l -

i ty . In a l l k i n d s o f n e w c l a s s i f i c a t i o n s y s t e m s , t h e r e i s a c l e a r l y n o t i c e a b l e

s t r i v i n g a f t e r m o r e e x a c t f o r m u l a t i o n a n d d e f in i t i o n . A t e r m l i k e m o r p h o -

m e t r y e x p r e s s e s t h i s id e a . N e v e r t h e l e s s , t h e r e p r o d u c i b i l i t y of c l a s s i f i c a -

t io n s y s t e m s p r e s e n t s a s o r r y s p e c t a c l e . E v e n w i t h s i m i l a r i n s i g h t s , g r e a t l y

d i f f e r i n g c l a s s i f i c a t i o n s c a n b e p r o d u c e d o n t h e b a s i s o f t h e s a m e m a t e r i a l .

T h e c o m p i l i n g o f c o m p a r a b l e s y s t e m s f o r d i f f e r e n t a r e a s i s s t i l l a n u n s o l v e d

p r o b l e m . T h u s t h e r e e x i s t s a s p e c i a l n e e d fo r r e p r o d u c i b l e c l a s s i f i c a t i o n

m e t h o d s a n d m e t h o d s w h i c h w i l l l e a d t o c o m p a r a b l e r e s u l t s . N u m e r i c a l

t a x o n o m y i s t h e n u m e r i c a l v a l u a t i o n o f t h e e x te n t o f s i m i l a r i t y b e t w e e n

t a x o n o m i c u n i t s a n d t h e a r r a n g e m e n t o f t h e s e u n i t s w i t h i n g r o u p s t a x a ) o n

t h e b a s i s o f t h e e x te n t o f s i m i l a r i t y . B r i e f l y , t h e m e t h o d i s a s f o l l o w s :

F r o m a n u m b e r o f s e l e c t e d s o i l s , a l a r g e n u m b e r o f c h a r a c t e r i s t i c s

a r e m e a s u r e d . T h e s e m e a s u r e m e n t s a r e m a d e s u i t a b l e f o r p r o c e s s i n g a n d

t h e e x te n t o f s i m i l a r i t y b e t w e e n a l l p o s s i b l e p a i r s o f s o i l s i s c a l c u l a t e d .

F r o m t h i s s i m i l a r i t y m a t r i x a g r o u p i n g i s s u b s e q u e n t l y c a l c u l a t e d . N u m e r -

i c a l t a x o n o m y c a n p r o v i d e p e r s p e c t i v e s a s it i s a m e t h o d t h a t c a n b e

r e p r o d u c e d , a l th o u g h i t w i l l l a t e r b e o b v i o u s t h a t t h i s i s s t i l l a v e r y t a n g l e d

a n d t r i c k y f i e l d .

D e s c r i p t i o n o f t h e m e t h o d o f n u m e r i c a l t a x o n o m y

T h e f o l l o w i n g d i a g r a m a p p l i e s f o r t h e c o m p i l a t i o n o f a l l c l a s s i f i c a -

t i o n s y s t e m s .

B o u n d a r y c o n d i t i o n s > g a t h e r i n g o f >- [ c o n s t r u c t i o n , t e s t i n g

b a s i c d a t a [ o f a s y s t e m

L

W e s t a r t b y f i x i n g th e b o u n d a r y c o n d i t i o n s : t h e c h o i c e o f a u n i v e r s e ,

o b j e c t i v e , e t c . N e x t b a s i c d a t a a r e c o l l e c t e d . B a s e d o n t h e s e d a t a a s y s t e m

i s c o n s t r u c t e d a n d t h e r e s u l t i s t h e n t e s t e d i n r e l a t i o n to th e o b j e c t i v e o f

t h e c l a s s i f i c a t i o n a n d , i f n e c e s s a r y , a d j u s t e d . T h e w h o l e p r o c e d u r e m a y

h a v e to b e r e p e a t e d s e v e r a l t i m e s . N u m e r i c a l t a x o n o m y c o n t a i n s r e p r o -

d u c i b l e m e t h o d s f o r t h i s p a r t o f t h e p r o c e s s . T h e v a r i o u s p h a s e s o f

p r o d u c i n g a n u m e r i c a l c l a s s i f i c a t i o n s y s t e m a r e a s f o l l o w s F i g . 1 0 ) :

1 ) T h e b o u n d a r y c o n d i t i o n s a r e f i x e d , c o m p l e t e l y i n c o n f o r m i t y w i th

t h e m a n n e r u s e d i n t r a d i t i o n a l s y s t e m s .

2 ) A s a m p l e , c o n s i s t i n g o f a l i m i t e d n u m b e r o f r e p r e s e n t a t i v e s o i l s ,

i s n ow t a k e n f r o m t h e c h o s e n u n i v e r s e o f s o i l s . W e s h a l l h a v e t o l e t t h i s

i n t e r e s t i n g s u b j e c t r e s t , a s i t d o e s n o t f o r m a n y s p e c i f i c p r o b l e m f o r th e

n u m e r i c a l m e t h o d s .

3 ) A c h o i c e i s m a d e o f l a y e r s a n d h o r i z o n s a n d of t h e c h a r a c t e r i s t i c s

b y w h i c h t h e s e a r e d e s c r i b e d , a s w e l l a s t h e m e t h o d s o f m e a s u r i n g t o b e

a p p l i e d . T h e c h a r a c t e r i s t i c s a r e t h e n m e a s u r e d , u s u a l l y i n a g r e a t n u m b e r .

1 80 G e o d e r m a , 4 1 97 0)

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1 2* 3* 4* 5*

choice of weighting coding

eterminat ion sampling

of boundary

c o n O o o s

un x i ~

layers and chara cterist ics measuring

horizons methods

6* 7 8* 9 10

t e s t i n g

hoice of rep res en tat io n sorting and

simi la r i ty in s imi la r i ty c luster ing

coeff ic ient \matr ix

representation in dendrogram

* = subjective choice

F i g . l O . D i a g r a m o f t h e c o n s t r u c t i o n o f s o i l c l a s s i f i c a t i o n s y s t e m s w i t h

t h e . a i d o f n u m e r i c a l m e t h o d s .

S o m e m e t h o d s e n a b l e t h e n u m b e r o f c h a r a c t e r i s t i c s t o b e l i m i t e d in a

r e p r o d u c i b l e m a n n e r o n t h e b a s i s o f t h e i r m u t u a l r e l a t i o n s h i p s . T h i s m e a n s

a c o n s i d e r a b l e s i m p l i f i c a t i o n o f t h e p r o c e s s .

( 4) A w e i g h t i s e i t h e r a s c r i b e d t o t h e c h a r a c t e r i s t i c s o r n o t . W i t h

t r a d i t i o n a l s y s t e m s t h i s h a p p e n s b e f o r e h a n d , a n d o n s u b j e c t i v e g r o u n d s .

W i t h n u m e r i c a l m e t h o d s a n a t t e m p t i s m a d e t o d o t h i s o b j e c t i v e l y a n d i n a

r e p r o d u c i b l e m a n n e r . B r o a d l y , t h e r e a r e t w o p o s s i b i l i t i e s :

( a) E a c h c h a r a c t e r i s t i c g e t s t h e s a m e w e i g h t , a n d w e c h o o s e a g r e a t

m a n y c h a r a c t e r i s t i c s , p r e f e r a b l y 4 0 o r m o r e . T h i s i s A d a n s o n s o l d

p r i n c i p l e . I t m a y s e e m o b j e c t i v e , b e c a u s e n o c h a r a c t e r i s t i c i s c o n s i d e r e d

m o r e i m p o r t a n t t h a n a n y o t h e r . T h e c h o i c e o f t h e s a m e w e i g h t i s i n f a c t

a l s o a n a r b i t r a r y , a n d s u b j e c t i v e d e c i s i o n . O n l y i n r e l a t i o n to t h e o b j e c t i v e

o f t h e c l a s s i f i c a t i o n c a n t h e s o u n d n e s s o f t h i s d e c i s i o n b e d e c i d e d .

( b) O n t h e b a s i s o f t h e r e l a t i o n s h i p b e t w e e n t h e c h a r a c t e r i s t i c s , a

w e i g h t i s a s c r i b e d o b j e c t i v e l y t o t h e c h a r a c t e r i s t i c s . T h e s e m e t h o d s a r e

r e p r o d u c i b l e , b u t th e c h o i c e o f m e t h o d i s s u b j e c t i v e .

( 5) T h e w e i g h e d c h a r a c t e r i s t i c s a r e c o d e d . T h i s u s u a l l y m e a n s a s u b -

d i v i s i o n in a l i m i t e d n u m b e r o f c l a s s e s , a d i v i s i o n w h i c h i s n o t w i t h o u t

i n f l u e n c e o n t h e r e s u l t s o b t a i n e d .

( 6) A s i m i l a r i t y c o e f f i c i e n t i s s e l e c t e d , i . e . a c o e f f i c i e n t s h o w i n g t h e

e x t e n t o f m u t u a l s i m i l a r i t y b e t w e e n t w o s o i l s . W i t h a p r o g r a m s e t up f o r

t h i s p u r p o s e t h e c o e f f i c i e n t s a r e c a l c u l a t e d f o r a l l p o s s i b l e p a i r s o f s o i l s

t h a t h a v e b e e n i n c l u d e d i n t h e s a m p l i n g .

(7 ) T h e r e s u l t o f t h i s c a l c u l a t i o n i s g i v e n i n a ta b l e , th e s o - c a l l e d

G e o d e r m a , 4 ( 19 70 ) 1 81

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s i m i l a r i t y m a t r i x . F r o m t h i s t h e e x t e n t o f s i m i l a r i t y b e t w e e n e a c h p a i r o f

s o i l s c a n b e s e e n .

8 ) A m e t h o d i s n ow c h o s e n t o s e t u p a c l a s s i f i c a t i o n s y s t e m f r o m

t h e s e d a t a in a r e p r o d u c i b l e m a n n e r ; t h i s is c a l l e d c l u s t e r i n g . S o m e

m e t h o d s w i l l f o r m c l u s t e r s w i t h l i t t l e m u t u a l r e l a t i o n s h i p w h i l e o t h e r

m e t h o d s w i l l p r o v i d e m u c h d e n s e r c l u s t e r s . T h i s w i l l l a t e r b e d e a l t w i t h

i n m o r e d e t a i l .

9 ) T h e r e s u l t o f t h e c l u s t e r i n g i s s ho w n a s a d e n d r o g r a m , s i m i l a r t o

a g e n e a l o g i c a l t r e e . In t h i s , t h e e x t e n t o f m u t u a l s i m i l a r i t y b e t w e e n t h e s o i l s

c o n c e r n e d c a n b e r e a d f o r e a c h s u b d i v i s i o n .

1 0) T h e c l a s s i f i c a t i o n m u s t b e t e s t e d a n d i m p r o v e d i f n e c e s s a r y .

Some criticism of the numerical taxonomy

T h e s e r e m a r k s o n t h e n u m e r i c a l t a x o n o m y o n t h e o n e h a n d c o n -

c e r n t h e e x i s t i n g e x a m p l e s i n t h e f i e l d o f s o i l s c i e n c e , a n d on t h e o t h e r ,

e x a m i n e th e q u e s t i o n i n h ow f a r t h e n u m e r i c a l t a x o n o m y i s o b j e c t i v e .

xisting examples of numerical taxonomy in the fi eld of soil science

T h e p h a s e s o f t h e m e t h o d w i l l b e d e a l t w i t h s y s t e m a t i c a l l y :

1 ) a n d 2 ) B o u n d a r y c o n d i t i o n s a n d s a m p l i n g . I n g e n e r a l b o u n d a r y

c o n d i t i o n s a r e n ot s h a r p l y d e f i n e d . E i t h e r o n l y a s m a l l n u m b e r o f g r e a t l y

d i s s i m i l a r s o i l s h a v e b e e n c h o s e n f r o m a l a r g e u n i v e r s e H o l e a n d

H i r o n a k a , 1 96 0; V o l o b u y e v , 1 9 6 7 ), o r u n i t s o n a l o w l e v e l of c l a s s i f i c a t i o n

h a v e b e e n s a m p l e d B i d w e l l a n d H o l e , 1 96 4; R u s s e l l a n d M o o r e , 1 96 7;

M o o r e a n d R u s s e l l , 1 96 7) .

T h e r e i s a n e e d f o r m o r e s y s t e m a t i c s a m p l i n g , a d a p t e d t o t h e l e v e l

o f t h e u n i t s w h i c h o n e w a n t s t o u t i l i z e i n t h e p r o c e s s i n g .

3) Layers and horizons. In various cases, layers and horizons have

been chosen on the basis of the horizon designations A, B, C etc.). This is

not objective. An objective definition of the standards to be applied must be

drawn up beforehand.

Several different approaches have been tried to overcome the problem

of vertical anisotropy. None of these is quite satisfactory. This is an impor-

tant subject for further study.

Characteristics: The choice of characteristics is a thorny problem.

This is usually a rather one-sided affair. For fundamental work, an attempt

must be made to choose a satisfactory combination of macro- and micro-

morphological, chemical and physical characteristics. Both genetic consid-

erations and those concerned with the application will play their part in the

arbitrary choice, along with the practical and financial resources available.

If international comparisons are to be aimed for, it will be necessary to

standardize in this field.

Some investigators have sharply decreased the number of character-

istics in a reproducible way on the basis of factor analysis Arnley, 1966)

or correlation coefficient Sarkar et al., 1966). This can simplify the further

processing and make it more intelligible.

Methods of measuring and analysing: There is, unfortunately, still

only very little international standardization of methods of measuring and

analysing. This is vital for the comparison of results.

4) Weighting. Weighting has already been described briefly. It is

obvious that this process has a great influence on the results.

182 Geoderma, 4 1970)

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(5) Coding. The manner of coding, which divides a characteristic

into several class es, influences the extent of differentiati on in the char act er-

istics applied for the calculation. It is easier to make a clear distinction

with a large number of classes per characteristic than with two classes.

(6) Similarity coefficient. There is still only a limited knowledge of

the influence of the various si mila rity coefficients. For the time being,

therefore, several coefficients in any case should be used alongside one

another. In soil science no experience exists in the field of the probabilistic

similarity coefficient (Goodall, 1964).

(8) Sorting. It has been proved in an investigation by Moore and Russell

(1967) that with different methods of sorting, especially at the higher

levels greatly differing results were obtained. Methods such as centroid

and flexible sorting conform most to the classical method by which soils

are allotted on the basis of a comparison with central concepts. For the

present, knowledge in this field is insufficient to allow methods for

particular materia l to be recommended.

(10) Testing. Testing of the resu lts of nu mer ic al t axonomy is still

virgi n country. Only when the objectives a re mo re cle arl y defined can an

attempt be made to measure whether the one method achieves the aim

better than another. In some cases information t heory could be used for

this p ur pos e (Shannon and Weav er, 1963; Hawk swor th et al., 1968).

Subjective versus objective in numerical taxonomy When we review the

methods of numerical taxonomy once again, it appears that subjective

decisions on numerous points are made with the choice of methods. The

method chosen determi nes the nature of the resul ts. Once the methods

are fixed the numerical classification within that framework is then ob-

jective and reproducible.

In the diagram (Fig.10) the subjective choices* can be readily indicated:

(1) It begins with the method of sampling, a part that is not character-

istic of the numerical method.

(2) Next, there are the choice and designation of layers and horizons,

and the choice of characteristics and methods of analyzing them.

In the specifically numerical part the following parts contain a subjective

choice: (1) the nature of the coding; (2) the alternative of ascribing weights

or not, and the method of determining weights; (3) the choice of a similarity

coefficient; and (4) the various methods of clustering or sorting, which can

lead to a whole range of systems.

There is still only very little known about the effects of the various

methods and whether they are suitable for certai n sort s of materi als. Each

application will thus have the character of a preliminary test, by which

different methods will have to be compared with one another.

One facet, inherent to numer ica l met hods, was not touched upon in

the foregoing. This is the opacity of what actual ly tak es pl ace during the

processing. The relationship is expressed by a number, but what this

similarity actually consists of remains a mystery. Methods of making this

intelligible will have to be sought if the essential objectives of classifica-

tion are to be arrived at, viz. the recognition of the similarity between parts

of the system. Moreover, methods will have to be developed to place soils

in the classes formed without the use of a computer. This is essential for

application in soil survey.

Geoderrna, 4 (1970) 183

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SOME PROPOSITIONS AND CONCLUSIONS CONCERNING SOIL GENESIS, SOIL

CLASSIFICATION AND SOIL SURVEY

eneral

I ll sociology (Zet terb erg, 1957) and geography (G arri son and Marble ,

1957) there are examples of axio matic methods for compil ing and des cri bin g

a theory. Although in this section an attempt will be made in this direction,

it will not be done with any pretension of presenting a balanced piece of

theory on soi l genesis , soi l c las sif icat ion and soi l survey. By pre sent ing

a number of aspects of these subjects in the form of proposi t ions and

conclus ions, an attempt will be made to make cl ear under what ass ump tio ns

soi l survey is pract ised. This f i rs t approach can be corrected on the basis

of crit icism. There is a need for a number of parts to be worked out

further a t a la ter s tage. Such a system can be useful for formulat ing re-

search projects in this f ie ld.

The bounda ry co ndit ions given on p. 173 als o appl y for the following

proposi t ions and conclusions.

The following is bas ed on the con cepts of Knox p.168. The gen era l l ine

of thought followed is that the pedon, as a sequence of la ye rs and horizo ns

wi th spec i f ic chara c te r i s t i c s i s the resu l t of ce r ta in geogene tica l and

pedogene tica l proces ses . As a resul t of the laws of so i l genes i s , in t e r r e la -

t ionships exist between those la ye rs and horizons. For this rea son the

pedon is defined as a cor re la t iv e complex (Viss er, 1949).

To avoid a number of complic at io ns, while a t the same t ime passi ng

over pro blem s of compound map uni ts , the fol lowing is a imed at deta i led

maps and uni ts of c lassif icat i on of the lowest level . F or rea son s of s imp lic i ty

the approach is non-probabi l is t ic . This means that in s ta t ing re la t ionships

these wil l be described as i f no random varia t ion according to the probabi l i ty

theory occur s . To approach r eal i ty, a l l fol lowing propo si t ion s and conclusions

should be interp ret ed in ter ms of this rando m varia t ion.

Propositions and conclusions

The genesis of the pedon

Proposi t ion 1. A re la t ionship exists between the external condi t ions

(s ta te fac tors ) and the pe rmanent char ac te r i s t ic s of the so il .

For the argumentat ion, ref ere nce is made to l i t er a tu re (Jenny, 1941, e tc. ) .

Two of the s ta te fac tor s - pare nt ma ter ia l and t ime - have prob -

lema tica l s ta tus. The parent ma te ri a l is s imult aneousl y a vi ta l part of the

soi l i tse lf and of the envi ronment in which the pedogenesi s takes place .

Although i t would be worthwhile workin g this ou tf ur the r , i t wil l suffice in

this art ic le that this is establ ished. In an area such as The Netherlands,

with a great deal of young deposits formed under the influence of wind and

water, an important part of the ch ar ac ter is t i cs of the pedon is deter mined

by sedimentat ion. Consequent ly, in the Dutch a t t i tude towards the genesis ,

geogenes i s occupies a spec ia l p lace . Pare nt mate r ia l i s at the same t ime

both pro ces s and sta te factor (see pro pos i t io ns 2 and 3). The t ime (Jenny,

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1941) is usually indicated as being a s tate facto r. Although I cannot ar gu e

this point on a philosophical basis, I am of the opinion that it is incorrect.

This does not mean that I consider the time less important. However, in

the following, the time will be dealt with in a different manner than was

the case with, for instanc e, Jenny (1941, etc.). The function of ti me is not

only the duration of the cour se of the present soil formi ng proc ess es. The

soil is a final product of processes that have changed with time, and of

the resulting accumulation, modifi cation and neutralization of thei r resp ecti ve

effects. A full treatment of this subject was considered too complicated for

this first approximation of the subject.

The questions su rroun ding the genesis of fossil soils will not be

considered.

Proposition 2. A relationship exists between the genetic processes

(pedogenesis and geogenesis) and the permanent cha rac ter ist ic s of the

soil.

Proof of this proposition is formed by the complex of the scientific

theory of soil science, geology and sedimentology and the results of exper-

imental pedology.

Conclusion 1. It can be concluded from the propositions 1 and 2 that

the general model is as follows:

input bla ck box output

state facto rs ~ genetic pro ces ses 3. soil

Within the frame-work of this article there is no need to elaborate

further on this model with the systems theory, or to indicate the feed back

etc.

he pedon as a complex of layers and horizons

Propositio n 2 can be elaborat ed furth er as follows:

Proposition 3. Geogenesis causes a certain sorting of solid particles,

which result s in a specific distribution of these partic les in horizont al

and vertical directions. This distribution occurs on the basis of geo-

genetic laws. These laws also govern the vertical sequence of layers,

resulting from varia tions in geogenesis over longer periods.

This proposition lies within the field of geology and sedimentology. It

can also be considered as part of the state factors. It is vital to soil survey.

Prop osi tion 4. Pedog ene sis is the cause of the development of a certai n

vertical sequence of horizons in the pedon. In time succeeding pedo-

genetical processes bring about a complex sequence of horizons.

Conclusion 2. It follows from the propositions 3 and 4 that the pedon

is composed of a specific sy ste m of laye rs and horizons, as a resu lt

of geogenesis and pedogenesis.

The pedon can be reg ard ed as a cor rel ati ve complex of a numbe r of

permanent soil characteristics in a certain vertical sequence (Visser, 1949).

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The pedou polypedo~z soil -laudscape body a~zd delineated soil body

Proposi t i on 5. A tende ncy exis ts in the genes is for local d ominat ion of

the inf luence of a l im ite d nu mbe r of s ta te fac tor s .

This is suppor ted by Stephens (1947) and by many regional soi l

inves t iga t ions .

Proposi t ion 6. In the f ie ld areas exis t withiu which s ta te fac tors vary

or have va r ied wi th i~ fa i r ly na r row l imi ts .

This means that at the edges of these are as, there is a max im um

late ra l r a te of change in s ta te fac tors . This propo si t i on is founded on the

geographical theory of s ta te fac tors and is outside the f ie ld of soi l sc ience .

This proposi t ion could a lso be formulated as: landscape bodies do exist .

Conclusion 3. I t fol lows f rom conclusions 1 and 2 and the proposi t ions

5 and 6 that are as may exist in the f ie ld, within which soi l condit io ns

vary or have var ied with t ime within fa ir ly narrow l imits . In other

words : so i l - land scape bodies do ex is t .

The soi l- l ands cape body is a geographi cal soi l body that is dis t i n-

guished by a maximum homogeneity, and by a maximum in la tera l ra te of

change of soi l ch ara ct er i s t ic s a t the boundary of tha t body, in a direc t ion

a t r igh t angles to tha t borde r . These s o i l - lan dsca pe bodies a re idea l so i l

bodies for soil survey from the point of view of homogeneity.

P ropos i t ion 7. A so i l c la ss i f ica t ion sys t em can be compi led loca l ly , which

which inc ludes po lypedons that a re ve r y s imi la r to so i l - l ands capeb odies .

On the basis of sam ple s taken f rom a uni ver se of pedons, a soi l c la ssi f i ca-

t ion syst em can be desi gned which is best su i ted to this univ ers e . This

may mean , for ins tance , tha t in the n-d ime ns i ona l p roper ty space , c l us te r s

a re d is t inguished which revea l in te r na l ly a maxim um homogene i ty and

mutua l ly a maxim um di f fe rence . A soi l c la ss i f ica t ion sys tem formed in

this way is not direc ted towards forming connected geographical soi l bodies .

It i s s ta ted in conc lus i on 3 that so i l - lan dsca pe bodies may be

dis t inguished which revea l in te rna l ly a maximu m homogene i ty . I t i s poss ib le ,

in pr inc ip le , to cons t ruc t a c la ss i f ica t io n sys te m of so i l - la ndsca pe bodies .

The most idea l sys tem of so i l c l a ss i f ica t io n for surv eying a ce r ta in geo-

graphic un iv ers e would then be a co mp rom is e between the two previ ous

clas sif ica t ions , in which the dema nds of both maxi mum ho mogeneity of soi l -

landscape bodies and maximum homogeneity of the c lusters of pedons and

polypedons are combin ed as well as possib le . As a s imp lif i ca t io n, the f ina l

phase of opt imizin g, e .g . , the optim izat i on in re la t ion to the applica t io ns of

the soil map, is omitted.

The la s t p ropo s i t ions and conc lus i ons re fe r re d to the cons t ruc t io n of

a su i tab le so i l c la ss i f ica t ion for so i l survey . In that b ranch of sc ience

which is engaged in the so -ca l l ed pat ter n recognit ion (Sebestyen, 1962) ,

th i s sub-d iv is ion i s denoted as pa t te rn de tec t ion . The s tep f rom so i l

c las sif i ca t i on syst em to a map legend conta i ns two aspec ts , both of which

are conn ected with the sc ale of the map and the geograph ic pa tt ern of the

so i l d i f fe rences :

(1) The opera t i onal dec is i on as to the percenta ge of imp uri t i es

a l lowed within the outer boundary of the polypedon, which is a t the same

time the boundary of the del ineated soi l body.

(2) The choice of cer ta in landscape bodies as del ineated soi l bodies

in those ca ses where , even with very deta i led sur veys, no fur t her polypedons

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can be distinguished. This deter mine s the most im port ant ar ea in which

soil classification and map legend diverge. Only what is opportune applies

here for the map legend.

The following sectio n deals with the possi bil ity of recog nizi ng the

disting uished units in the field. Sebestye n (1962) call s this patt ern

recognition . The usual practice in soil survey is that delineated soil bodies

are depicted on the map on the basis of a few observations of the soil itself

(by means of borings or profile pits), and on the basis of field c ha ra ct er-

istics, theory and experience.

Proposition 8. Field characteristics exist which give indications as

to the boundaries of (soil-)landscape bodies.

These field cha rac ter ist ics are ex trem ely complex. They contain state

factors (such as vegetation, relief, groundwater level), soil characteristics

visible on the surface, observ ation s of the re acti on of the soil to external

interventions or circumstances (such as the difference in reaction to vehicle

traction, to tillage, to trampling by cattle, to drying out etc.), as well as the

reaction of the plant growth on the soil (good or bad growth etc.).

The number of direct observations which provide indications as to

where the borders are situated is small. Moreover, they usually only have

a bearing on the surface of the soil. The remaini ng observa tions provi de

indirect prognoses concerning soil conditions. These prognoses are founded

on the knowledge of mutual relationships that have been given, for the

greater part, in the above propositions and conclusions. This proposition

is partly founded on the above, including conclusions 1 and 2.

Because of the complexity of this proposition, no attempt will be made

to fit it into any rigid scheme.

Conclusion 4. Based on conclusion 3, on the propositions 7 and 8 and

on observations of soil characteristics made at borings or profile pits,

and on the basis of the available theory (including conclusions 1, 2 and

3), it is possible to note the boundaries of delineated soil bodies in the

field, and to map them.

The gre at signi ficance of knowledge and exper ien ce in mapping

delineated soil bodies can perhaps best be illustrated by an example.

A soil surveyor working near Wageningen,to the south of the Rhine, is

confronted with the following situation: Along with a number of augerings of

fluventic eutrochrepts (Fig.ll,E) with heavy clay on sand, he finds one spot

of fluventic haplaquept (Fi g. ll ,H ) with gre y heavy clay to a great depth. He

use s the following knowledge to tra ue a bor der . He knows from g eological

data and a general reconnaissance that the area consists of alluvial

deposits. The knowledge of the general pattern of such deposits with sandy,

higher levees, enclosing heavier depo sits in the silted st rea m channel

(Fi g. l l , cross section A-B ), s i tuated together among lower, heavy back

swamps, provides him with the following choice.

The boring (H) refers either to a stream channel (Fig.ll,H1) or to a

back swamp (Fig.ll,H2 ). The fir st can be reco gnize d by the relief as a

meandering depression between two levees. If there are no indications

in the relief, a decisive answer as to the choice between back swamp or

str eam channel can only be obtained by bori ngs in the surroundings. This

strongly simplified example gives a rough idea of the significance in soil

survey of all kinds of theoretic considerations and especially those that

indicate possible patterns in soil conditions.

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p

E = Fluv enti c Eutrochrept

H2 E H1 E H2 H = Fl uv en ti c Haplaq uept

cross sect ion A B

F i g . l l . S c h e m a t i c s o i l m a p o f a r i v e r c l a y a r e a .

I n t h e i r m o s t e x t r e m e f o r m , t h e s e c o n s i d e r a t i o n s p l a y t h e i r p a r t in

t h e i n t e r p r e t a t i o n o f a e r i a l p h o t o g r a p h s , w h e r e , o n t h e b a s i s o f i n f e r r e d

f e a t u r e s o n ly , a t t e m p t s a r e m a d e t o f o r e t e l l c h a r a c t e r i s t i c s o f a r e a s

w i t h ou t a n y d i r e c t o b s e r v a t i o n s o f s o i l c o n d i t i o n s i n t h e f i e ld .

DISCUSSION

eneral

I n o r d e r t o c o n d u c t r e s e a r c h , i t i s n e c e s s a r y t o h a v e a n o v e r a l l

p i c t u r e o f t h e p r o b l e m s w i t h i n th e f i e l d o f i n v e s t i g a t i o n . O n th e b a s i s o f

a u n i f i e d s c h e m e o f p r o p o s i t i o n s a n d c o n c l u s i o n s , i t c a n b e d e t e r m i n e d

w h i c h a s p e c t s o f t h e t h e o r y h a v e b e e n s u f f i c i e n t l y p r o v e d a n d w h e r e t h e

w e a k s p o t s l i e .

I n t h e f o r e g o i n g s e c t i o n s , t h e l in e h a s b e e n t a k e n t h a t a c l o s e r e l a t i o n -

s h i p e x i s t s b e t w e e n p e d o g e n e s i s , s o i l c l a s s i f i c a t i o n a n d s o i l s u r v e y .

P e d o g e n i c r e s e a r c h i s o f t e n c o n s i d e r e d t o b e a s e p a r a t e d i s c i p l i n e w i t h

i t s o w n o b j e c t i v e . I n t h e f i e l d o f s o i l c l a s s i f i c a t i o n a s w e l l , t h e r e a r e l o c a l

t e n d e n c i e s t o w a r d s t h e s t u d y of t h i s s u b j e c t f r o m a p u r e l y s c i e n t i f i c

p o i n t o f v i e w .

H o w e v e r , a g r e a t n e e d e x i s t s f o r r e s e a r c h w h i c h c a n p r o v i d e a b a c k -

g r o u n d f o r s o i l s u r v e y . T o t h i s e nd , a n i n t e g r a t i o n o f p e d o g e n e s i s , s o i l

c l a s s i f i c a t i o n a n d s o i l s u r v e y s h o u l d b e a i m e d f o r . W h a t t h i s i n v o l v e s f o r

t h e r e s e a r c h t o b e u n d e r t a k e n i s o u t l i n e d b r o a d l y b e l o w .

1 88 G e o d e r m a , 4 1 97 0)

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edogenesis

Pedogenesis forms one of the fundamentals of soil survey. Of old, the

relationship between state factors and the soil has always occupied a focal

point of interest. The relati onship s that resul t f rom this study take the

character of a correlation between phenomena. These correlations are of

great importance for the practical side of soil survey. The disadvantage of

this approach is that less attention is given to soil forming proc esse s. Only

by a knowledge of these p ro ce ss es can the actual causal connection be

revealed. With the aid of this causal connection, a better characterization

of the state factors can be arrived at.

Along with the extremely import ant purely scientific res ear ch of

pedogenesis, another form of pedogenic research must come into being,

one directed more towards soil geography.

Constantly recurring patterns exist in soil conditions. These link up

with patterns of state factors. By drawing up hypotheses on pedogenic and

geogenic pro ces ses aimed at explaining these r ecur rin g patterns, and by

putting such hypotheses to the test in the field, it is possible to explain

more fully the variations found in soil conditions, both qualitatively and

quantitatively.

Referen ce has already been made to the investigation into the geo -

che mis tr y of landsca pes (Polynov, in Parf enova , 1963; Kovda et al., 1968).

Res ear ch of this. kind, combin ed with the analysi s of the geograp hic di st ri -

bution of the soils, is a very impor tant b asis for soil survey.

In the field of geogenesis too, basic research is indispensable for soil

survey. Edelman strongly stimulated this research, and many contributions

in this area have been made by the group of Dutch field pedologists. In

other places as well it is apparent that more and more attention is being

given to these subjects: publications by Butler (1950), Mulcahey and

Hingston (1961), Mulcahey and Hum phri es (1967) and other Aust rali ans, Ruhe

(1960), Ruhe and Walker (1968) in America, etc. Application of the theory

of open and closed systems are to be found in reports by Chorley (1962),

Ruhe and Walker (1968) and Walker and Ruhe (1968). In The Netherlands

a geomorphologic map is being prepared , under the leadership of

Maarleveld of the Soil Survey Institute, together with the State Geological

Survey. Through this map, cer tain aspects of the relation between soil

survey and geogenesis can be more fully studied.

Soil classification

Since the beginning of the scientific study of soil, the connection be-

tween pedogenesis and soil c lassifi cation has always occupied the centre

of interest.

Soil classification can be studied quite apart from soil survey.

Kubi~na's sy ste m is an example of this. The sch eme which came into being

in this way can be in complete conformity with the existing pedogenic

views. It does not necessarily mean, however, that this offers an optimum

scheme for soil survey as well. Soil classification is an arrangement of

p edons in such a way that the mutual

similarity

between pedons

within

each

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unit is the optimum, and at the same time the mutual

d i f f e r e ~ z c e b e t w e e ~

the units is the optimum. With soil survey, on the other hand, soil bodies of

grea te r hor izonta l d imens ion so i l - lan dscap e bodies, de l inea ted soi l bodies)

are c las sif i ed in such a way that these uni ts po sse ss an opt imum interna l

homogeneity and differ mutually in an optimum way. At the same time, the

scheme must meet the requirement that i t is connected with the object ive

in the most optimum way.

The soi l c lass if ic at ion and the map legend for soi l surve y wil l have

to form a compr omis e between these thre e opt imizing methods. I t is of

great importance that this subject be s tudied further by the most object ive

res ear ch methods, including nume rica l taxonomy. The use of nume rical

methods for the development of soi l c lass if i cat i on sys tems f or la rge scale

soi l maps for specific appl icat ions is of great interest . This subject is

under in vest igat ion in The N etherl ands Soil Survey Inst i tute .

o i l s u r v e y

Res ear ch in the f ie ld of soi l sur vey is among the undeveloped are as

of soi l sc ience. This is a l l the more r