%&a qwel-f2 p,"a,,be- S S S A - T ; CONSEQUENCES OF HEAVY MF,CHANIZATLON AND NEW ROTATION ON RUNOFF

AND ON LOESSIAL SOIL DEGRADATION I N THE NORTH OF FRANCE.

(Summary of the paper no 92, Session I , Honolulu,$1983) +-- k f f by ROOSE (E.J,)* and MASSON (F.X.)

The impact of,heavy mechanization on s o i l degradation raises consi-

derable problems a l l over the world. The authors present some r e s u l t s of a

l i g h t approach t o this problem promoted by a committee of c u l t i v a t o r s with

the he lp of t he Administration and some researchers i n the North of France.

This approach combined reg iona l inves t iga t ions and f i e l d tests t o

evaluate the extension of erosion and the reasons f o r s o i l degradation. Six--

t y r a i n f a l l simulated tests were appl ied on lm2 p l o t s with the OFSTOM spr in-

k l i n g i n f i l t r o m e t e r t o study the evolut ion of i n f i l t r a t i o n during an annual

r a i n f a l l event (33" i n one hour) and s o i l e r o d i b i l i t y . In s p i t e of the low

e r o s i v i t y of the r a i n f a l l (Rmetric = 5 0 ) , eros ion i s active i n a l l t he loes-

s i a l area, bu t i t s i n t e n s i t y depends on the type of c u l t i v a t i o n (covering i n

win ter , res idue management), s o i l degradation ( ac id i f i ca t ion , c rus t ing , com-

pact ion) and the i n t e n s i t y of s o i l t i l l i n g (d i lu t ion of organic matter and

topso i l pu lver iza t ion) . The increase i n e ros ion i s r e l a t e d t o the development

of mechanization, the d issoc ia t ion of breeding and farming and the extension

of degrading i n d u s t r i a l crops and n o t t o an hypothetic modif icat ion of t h e

r a i n f a l l pa t t e rn . F i e ld tests showed t h a t runoff i s very high (40 t o 85 Z ) i n

s o i l s degraded by i n d u s t r i a l r o t a t i o n and mechanized farming ( sea l ing c r u s t

and t l l l a g e pan). Subsoiling can only temporarily and p a r t l y remedy compacted

pan. The more advanced the seedbed prepara t ion i s , the more considerable run-

off i s (5 t o 66 Z) and the g rea t e r t he d i f f i c u l t i e s of germination f o r ce-

reals. The authors cctvCL.q$tthat i t i s necessary t o reduce the number of t i l l a g e

p rac t i ces , t o cover the s o i l i n winter and t o r e s to re the balance between the

r o t a t l o n of degrading crops and r e s t r u c t u r a t i n g ones. Therefore, t e r r ac ing

does not seem necessary.

Dr ROOSE, Di rec teur de Recherche en Pédologie à l'ORSTOM, 24 rue Bayard, 75008 Pa r i s , FRANCE e t Lab. Hydrogéologie; Univers i té Orléans 45046, FRANCE

-2.-

INTRODUCTION

I n the earliest cropping systems, a long period of fallowing makes

i t poss ib le f o r s o i l s impoverished by a shor t period of cropping t o recover

'

both a c e r t a i n l eve l of chemical f e r t i l i t y and good physical p roper t ies .

This system ca l l ed s h i f t i n g cu l t i va t ion i s s t i l l la rge ly widespread i n spar-

s e l y populated t rop ica l zones (FAO, 1974). I n Europe, a f i r s t a g r i c u l t u r a l

revolut ion allowed t o reduce the period of fallowing and t o i n t e n s i f y the

a g r i c u l t u r a l production through a c lose assoc ia t ion between breeding and

farming including t i l l i n g , manuring and ro t a t ion between degrading and re-

s t r u c t u r a t i n g crops (temporary grassland and ce rea l s ) . I n the ea r ly century,

. i n d u s t r i a l i z a t i o n brought new modifications to agr icu l ture . Mechanization

he lps t o release manpower f o r the preparat ion of the seedbed, weeding and

harvest ing. Mineral f e r t i l i z a t i o n contr ibutes t o p l an t n u t r i t i o n , bu t crop

r o t a t i o n tends t o produce more and more i n d u s t r i a l crops which lead t o s o i l

degradation. Breeding i s concentrated i n special areas c lose t o the farm

where i t becomes a po l lu t an t . However, one i s not long i n observing t h a t

s o i l physical p roper t ies are only p a r t l y and temporarily improved by til-

l i n g .

Up t o the present time, in tens ive mineral f e r t i l i z i n g and advanced

p l an t breeding led t o a very high product ivi ty . Eowever, as i n many places

over the wor ld (TRIPLETT, MANNERING, 1978 ; BOIFFIN e t a l . , 1982, W A R ,

1982), one begins t o observe s tagnat ing and even decreasing y ie lds desp i te

l a rge amounts of f e r t i l i z e r s .and s t rong cu l t i va t ion prac t ices , the degra-

da t ion of the s o i l physical p roper t ies , the surface waterlogging of the

p la teau loamy s o i l s , the abundant runoff leading t o the gul ly erosion of

h i l l s i d e s , frequent inundations

v i l l a g e s . The frequency and i n t e n s i t y of these problems of erosion increa-

sed so much over the l a s t t en years i n the northern p a r t of France tha t the

c u l t i v a t o r s themselves have ca l l ed upon the help of t he Agricul tural depart-

ment , a few researchers and the Rural Development Committee of t he Ya1 de

and mud deposit ions i n va l leys occupied by

- 3 -

Canche in order to cope with the situation. (MASSON, PELLETIER, 1979 ; DOUAY

et al., 1980).

The impact of mechanization on soil degradation is such a widespread

problem all over the world that it seems necessary to describe here the re-

sults of a 1igh.t approach to this problem in a country region.

METHODOLOGY

Cultivators: are not interested in undertaking on a local basis high-

l y sophisticated researches on processes of erosion. But they need to determi-

ne the extensi’on and economic influence of erosion, the causes and factors of

soi3 degradation. They would like to get the most adequate but the less deman-

ding conservation practices with a view to the development of a modern and

prof2talile agrlculture. Therefore, we made successive approaches to the pro-

hlem i’n order to specify it and modify gradually the reaction of cultivators

towards the eroslon risks and the possible changes in the current farming

practices wi’th a view to reaching a steady production which will be better

adapted to the local’ecolog2cal and socio-econcmic conditions.

Three investigatlons have been made successively :

Ell at the leyel of the local administration of the Ya1 de Canche in order to

evaluate the extension of damages caused by erosion in the most affected

zone of the department.

E2 at the level of.the cultivators and plots in order to, look for the reasons

f o r the change In the intensity of erosion since about ten years.

Eg at the level of the North-Pas de Calais region by studying the historical,

geomorphological and soil data related to phenomena of erosion visible in

the fleld and in aerial photographs.

x Simultaneous.ly, various agricultural experts (INRA, ORSTOM and INA )

_ _

INRA = Institut National de la ‘Recherche Agronomique. ORSTOM = Office de la Recherche Scientifique et Technique Outre Ner. INA = Insti’tut National Agronomlque.

were asked to get into touch with cultivators in the field and make an evalua-

tion of the situation. In addition to the classical Department of Agricultu-

re, a special committee has been set up in order to give advice to farmers

in the most affected region.

Finally, as problems and solutions seem to be clearer, field tests

have been made with voluntary farmers in order to evaluate the influence of

intermediate crops on the soil cover in winter or that of the excessive til-

ling on germination and the cereal production. Similarly, the Department of

Vater 'Management undertook 65 rainfall simulated tests through the sprinkling

2nf2ltrometer developed By ORSTOM (ASSELINE and VALENTIN, 1978). These tests

allow to study the evolution of infiltration (over lm2) during an annual rain-

x

fall event (33mm in one hour) as well as soil erodibility in relation to va-

ri'ous factors such as the soil type, the green cover, farming practices, sur-

face roughness and structure and cropping systems. Two series of tests through

the inf2ltrometer wi'll demonstrate the impact bf the change in the cropping

sys,tem (rotation and mechanization) and the intensive tilling on the erosion

risks.

STUDY ENVI'RONMENT

Investlgatrons were made in the 'Ya1 de Canche which is situated in

the north OP France between R r r a s and 'Montreuil (cf. situation map), The

landscape i's composed of vast loessial plateaus (where large-scale farming

is developing) interrupted by deep valleys with steep convex-concave slopes

where are concentrated bxeeding and forests (cf. geomorphological cross-sec-

tion). The most frequent soils are more or less leached acid brown soils on

loess whi'ch are all the more sensitive to crusting as they have been expioi-

ted since centuries : thei'r texture is loamy to sandy loamy, their organic '

matter content is low (.often less than 3 X) and these soils become acid in

the absence of 1hi.ng. The advanced mechanization over 15 to 30 years. led

to the formation of a rather thick compacted pan (20 to 40cm) under a

- s- ~: ‘ I

ploughed horizon (30cm) ( c f . descr ip t ion of a p r o f i l e as an appendix). Simul-

taneously, the r o t a t i o n which included two years of cereals and one year of

sugar-beets has been increased with i n d u s t r i a l p lan ts whose s o i l cover i s

low, sowing i s late and crop residues are s m a l l (sugar-beet, potatoe, maize

and various vegetables for cannery). Intermediate crops, green manuring and

temporary grasslands have been given up : only humid s o i l s a r e exploi ted as

permanent grasslands (MASSON, PELLETIER, 1979).

The region ge ts a r a the r moderate oceanic temperate climate. The

mean minhum temperatures drop from 13°C i n Ju ly t o 1 , 4 ” C i n January and ma-

ximum temperatures from 20,6.’C t o 6 ,4 ”C i n the same periods. Mean annual

r a i n f a l l s amount t o 850” and t h e i r annual d i s t r i b u t i o n i s steady with mini-

mum monthly r a i n f a l l s amounting t o 50” from February t o May and maximum

ones amounting t o 116m i n November (PETIT-RENAUD, 1980). The mean e r o s i v i t y

index of WiscIimeier (J960) (Rmetr ic ) i s about 50 (PIHAN, 1978). Therefore,

rai’nfalls a r e general ly not heavy, apa r t from a few summer storms. Winter

(not very k a v y r a l n d a l l s over a long period of t i m e on crusted bare s o i l o r

in tlie thawing peri’od) and spr ing (storms on too pulverized s o i l i n May-June)

a r e c r i t i c a l periods for erosion.

‘RESULTS

A. Inves t lga t ions

Inves t iga t ions which were made w i t h the country adminis t ra t ion

(E]) and the farmers (E2) allowed t o observe t h a t phenomena of erosion are

la rge ly found i’n the whole zone of l o e s s i a l plateaus. However, t h e i r i n t ens i -

ty var ies w i th the type of cu l t i va t ion (importance of s o i l cover i n winter

and spr ing, more or less considerable r e s t i t u t i o n s of organic mat ter t o s o i l ) ,

with the s o i l degradation ( ac id i f i ca t ion , s ea l ing c rus t s , compacted t i l l a g e

pan) and with the depth and i n t e n s i t y of t i l l i n g . As a matter of f a c t , the

general deep t i l l i n g leads t o the d i l u t i o n of s o i l organic matter and reduces

i t s s t r u c t u r a l s t a h i l i t y a l l the more s o as s o i l s are pulverized i n order t o

- 6- i

prepare the seedbed. The increase in4weight and the number of passes by the

d i f f e r e n t kinds of equipment can only increase hydraulic d i s c o n t i n u i t i e s and

the compactness of deep horizons. Since then, i t seems t h a t the increase i n

the i n t e n s i t y and frequency of phenomena of e ros ion i n the no r th of France i s

r e l a t e d t o the development of mechanization, the d i s soc ia t ion of breeding and

c u l t i v a t i o n and the increas ing areas covered w i t h degrading crops r a t h e r than

t o an hypothetic change i n t h e r a i n f a l l p a t t e r n . F ina l ly , t he t h i r d investiga-

t i o n and t h e mapping of s o i l e r o d i b i l i t y i n the whole department showed t h a t

the organic matter content i s the lowest and s o i l s are the most degraded where

the mechanized i n d u s t r i a l c u l t i v a t i o n has been introduced s ince a longer pe-

r i o d of time, such i s the case of the regions of ARTOIS and CAMBRAISIS. I n the

o t h e r sub-reglons, slieet and gu l ly e ros ion exist but are l imi ted in ' space, ei-

ther f o r geomorphological reasons (slopes are shor t or too gent le ) o r f o r rea-

sons of land use p rac t i ces (meadows, bush, hedges or old embankments w h i c h

absorb or reduce runoff ) .

B. The i n f i l t r a t i o n tests i n the f i e l d

A f i r s t serie of tests showed t h a t the increase i n runoff varies

w i t h the cropping system such as t h e o ld system where breeding i s c lose ly re-

l a t e d t o c u l t i v a t i o n and the present system where heavy equipment i s used t o

p l a n t and harves t various i n d u s t r i a l crops.

Table I c l e a r l y shows t h a t runoff begins later and remains lower

i n the o ld cropping system where breeding i s c lose ly assoc ia ted with cu l t i va -

ti'on tIian i n t h e present i n d u s t r i a l system which i s highly mechanized and

leads t o the formation of t i l l a g e pans and sea l ing c r u s t s .

Subsoiling ( t e s t 4 ) can cope p a r t l y with these d i f f i c u l t i e s , bu t

?t i s expensiye and a l l the less e f f e c t i v e as the s o i l i s i n s t a b l e ( f o r instan-

ce , ac id loamy soi ' ls) . Tests 2 and 1 4 show how quick and abundant runoff i s

(hard ly 15 % of r a i n f a l l perco la te ) i n i n d u s t r i a l crops whose harves t has j u s t

beezi made : t he s o i l i s crusted by r a i p f a l l s and compacted by t r a c t o r s and

- f -

trailers.

I n the second serie of f i e l d tests, a study w a s made on the in f lu -

ence of s o i l pu lver iza t ion on the shooting of a cerea l as w e l l as on runoff

during the preparat ion of the seedbed.

The r e s u l t s of Table II show t h a t the more pulverized topsoi l i s

through successive vibro-driven o r rapid passes of various types of harrow,

the higher runoff i s and the less l i k e l y are the ce rea l seeds t o germinate

(asphyxia) and go through the sea l ing c rus t .

DISCUSSION

Despite the low e r o s i v i t y of r a i n f a l l s (R = 50) and t h e i r homogeneous

annual d i s t r i b u t i o n , one can observe numerous phenomena of erosion, runoff and

sedimentation i n the zone of l o e s s i ä l plateaus i n the North of France. They

most of ten occur i n winter on denuded and very sa tura ted s o i l s l i k e l y t o be

subject t o a l t e rna t ions of f r o s t and thaw ; sometimes, erosion occurs i n

spr ing (May-June) on hardly sowed f i e l d s when the s o i l has been too much pul-

verlzed. S i m i l a r phenomena occur i n Belgium (De PLOEY, 1979, BOLLINE, J982)

and England (NORGAN, 1979).

Tliese phenomena of erosion are not new l n France s ince a survey ma-

de by HENIN and GOBILLOT (3950) revealed t h a t 4 t o 5 mil l ions of hectares were

suhject t o erosion. On the contrary, what i s recent (since 10 t o 20 years) i s

the frequency of inundations and gullylng as w e l l a s

ges r e su l t i ng from : - the change i n ro t a t ion (fewer residues i n s o i l ) ,

the considerable dama-

- a more advanced and heavier mechanization (as s o i l s

a re degrading) and more frequent operations i n order t o remedy the increase

i n s o i l compactness ( ins tab le s t ruc tu re with low organic matter conten ts ) ,

- an increase i n the f i e l d a rea (destruct ion of hedges

and downhil l extension of p l o t s ) ,

- and f i n a l l y the decreasing r e s t i t u t i o n s of organic

- 8- * '

mat ter t o s o i l (fewer cereals, burn t straw? and d i l u t i o n of organic matter by

means of deep t i l l i n g ) .

I n t r o p i c a l regions, the d i sa s t rous e f f e c t s of the highly mechanized

crops occur more r ap id ly (G. MARTIN, 1963 ; CHARREAU and FAUCK, 1970) as a re-

s u l t of t he more aggres,sive c l ima t i c conditions (ROOSE, 1977) and the more ra-

p i d minera l iza t ion of organic matter (ROOSE, 1980). S o i l s are compacted, wa- z

terlogged and give r ise t o sea l ing c r u s t s over a few years. I n Senegal, one

could observe se r ious phenomena of e ros ion even on gent le s lopes ( ( 2 X) two

years a f t e r land c l ea r ing . I n the f o r e s t zones of t he Ivory Coast, mechani-

zed c u l t i v a t i o n raises similar problems (BLIC, 1976, BLIC and MOREAU, 1977).

However, i t i s obvious t h a t i t i s no t poss ib le nowadays t o cons ider ,

t he suppression of mechanization f o r socio-economic reasons. Therefore, one

must t r y t o reduce

ses and the weight of the d i f f e r e n t kinds of equipment and by using biologi-

cal methods together wi th smooth mechanical methods i n order t o b e t t e r ex-

p l o i t s o i l s without degrading them. This so lu t ion i s poss ib le nowadays as

long as s o i l has not been too eroded, which i s generally the case i n tempe-

rate regions where phenomena of e ros ion are less in t ense than i n mediterra-

nean or t r o p i c a l regions.

i t s degrading influence by l i m i t i n g the number of pas-

CONCLUSIONS

Heavy a g r i c u l t u r a l mechanization degrades the s o i l physical proper-

t i e s on the sur face and i n depth and f i n a l l y reduces s o i l p roduct iv i ty i n

t r o p i c a l regions where degradation i s very r ap id or i n temperate regions

where i t i s slower. Mechanization o f t en leads t o use more and more frequent-

l y heavier and heavier equipment i n order t o achieve a deeper mellowing of

s o i l whose s t r u c t u r e i s degrading. However, the r e s u l t i n g macroporosity

does not l a s t long i n i n s t a b l e environments such as loes s i f the S t ruc ture

s t a b i l i t y i s not improved e i t h e r by i n j e c t i o n of f loccu la t ing ions Climing)

or by the growth of deep rooted crops (temporary grassland of lucern or ray

- 3 -

grass) e

Finally, it will be necessary to restore the balance between the ro-

tation of degrading plants and that of restructurating plants or to find out

a new cropping system likely.to regenerate the structure and macroporosity

(temporary grassland, forage growing), to cover soil during the long cold

season (winter grain, green manuring) and to limit the number of motorized

operations. Heavy agricultural mechanization leads to the degradation of the

environment, which does not question the socio-economic value of mechaniza-

tion but requires some effort to adapt it to the physical conditions of the

environment and to man.

Table I : Influence of t he cropping system on the s o i l degradation and runoff during a one hour simulated r a i n of 1 O F I

33" i n win ter .

Treatments

Depth of ploug- hing

T i l l age pan

S o i l sur face conditions

Green cover

Runoff

Delay ?n mn

Runoff i'n rmrl

Nean K'R i-n %

Fi'nal KR ?n % a f t e r 6.Omn

Number of t e s t

*

Horsepower t r a c t i on

Winter bar ley

J 7cm

O

cloddy

80 %

. .

69''

o"

0 %

o %&

16

Permanent grassland

- O

compacted oyer 15cm

J O 0 %

. .

1 6 '

2" 6 %

24 %

58

Broken g ras s 1 and

25 cm

+

s m a l l clods

7 %

. . . .

35'

9" 27 %

48 %'

57 . . ,

T i l l i n g

Stubble ploughing

Subsoiling

c.

25cm

+ ( in te r rupted)

s m a l l ' clods

10 z S tuhh 1 e . . . .

15'

5"

15 %

30 %*.

4 . -

- ~~~ ~

T i 1 l i n g

Stubble ploughing

No subsoi l ing

25 cw

+ +

small clods

JO z Stubble

4'

J 4 mm

42 Z

73 . %

6 . .

Ieavy equipment a f t e r harves t ing

Sndives

30cm

+ + +

:rusted

1 1 %

les idue s

I '

23mm

85 7

91 z 2

potatoes

30cn)

+ + +

crus ted

1 1 z Residues

2'

2 8 m

85 Z

.98 %

.14

The s t a b l e minimum i n f i l t r a t i o n rate has no t been ab ta ined after 60 minutes of r a i n f a l l . Rains a re simulated on ac id brown s o i l s i n l o e s s i a l p la teaus . The s lope i s lower than 5 % - KR = runoff c o e f f i c i e n t = depth of runoff/depth of r a i n f a l l .

L .

FIG S.

Scale. L-I /loo.oOO Ech Hæ1 /lO.OOo

- Crbtacé supérieur (craielchalk ) 0

Fluvia t i 1 Alluvion

. . . .

w

I u z a 5

Echelle : Scale : I/I.OOO.OOO

Fi Primaire + Jurassique i Crétacé inf.

I I Crétacé sup.+ L i mons

1-1 Tertiaire Sableux

Quaternaire Fluviatile ou marin

I d

Table II : Influence of t h e i n t e n s i t y o f - , s o i l t i l l i n g on t h e shooting of w’keat &VI& QII

brown soil on loam : Campagne-lez-Hesdin y March 1982.

runoff during a one hour simulated r a i n of 33”. Acid

I

T r e a tment

Number of Tasses

Number of shootings / & e

Runoff [mm

l i l l i n g

- sowing

2

I27

176

5 %

Cil l ing

Harrow 4cm 1 Coupled L sowing

2

I14

.9,1

28 %

Sources ‘ DERANCOURT (1982)

r i l l i n g

More ra- pid har- row 8km/h

2 (more rap id)

1 O9

12,5

38 %

T i 11 i ng

1 vibro- dr iven cu l t iva- t o r

1 sowing

3 (deeper)

7 3

18,8

57 %

* MASSON (1982)

r il 1 ing

2 vibro-driven cul- t i v a t o r s

Sowing

4

59

21,7

66 X

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- BLIC (Ph. de), MOREAU (R.), 1977. Evolution des caractères structuraux des sols ferrallitiques sous l'effet d'une mise en culture mécanisée récente en Côte d'Ivoire préforestière. Com. IITA, Ibadan, 6-10/2/1977. Orstom Abidjan 15p.

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Annexe 1 - Qucck profile description of a brown leached soil of the Mouriez plateau (North of France).

The description was made by Mr. MASSON in Marsh 1981 on a wet field of cereals, 4 % slope, on the plateau near Mouriez.

O to 1 cm Sealing crust(thick variation from 1 to 4 centimeters).

I to 25 cm Ap. horizon : brownish grey (7,5 YR 4/4), silty loam, low or- ganic matter content (% 1 %>, traces of calcareous improve- ments, medium polyedric structure, high porosity, fine roots. Distinct transition on the tillage bottom (around 22 to 30 cm).

25 to 50 cm AZ horizon : yellowish brown (7 YR 5/6) loamy, rare traces of organic matter and calcareous improvements, prismatic 'to cubic structure becoming massive on the level of the tillage pan (15 to 25 cm thick, very compact) and below very rough poly- edric structure. Very rare roots located on the structural si- des and again dividing themselves under the compacted level. Transition rather distinct (around 5 0 to 75 cm).

50 to 85 cm Bt horizon : brownish yellow (7 YR 4/6) clay loam, clay skins, and rough to medium polyedric structure, better rooting and higher under interstructural porosity ; less compact than above.