Laboratory experimental study of soil crusting: Relation between aggregate breakdown mechanisms and crust stucture

I CATENA

vol. 16, p. 377-392

Cremlingen 1989 J

LABORATORY E X P E R I M E N T A L S T U D Y OF SOIL C R U S T I N G : RELATION B E T W E E N AGGREGATE BREAKDOWN MECHANISMS A N D CRUST S T U C T U R E Y. Le Bissonnais, A. Bruand & M. Jamagne, Orleans

Summary

R6sum6

Crusts formation on cores of air-dry and prewetted aggregates was studied, using a laboratory rainfall simulator. Samples were taken out during the experiment, in order to study changes in water content and aggregates size distribution inside the crust and under the crust. Pore space geometry of the crusts is described using light optical microscopy and mercury porosimetry. In the case of air-dry aggregates, aggregates become micro-cracked. Macropores at the surface are quickly closed and ponding occurs rapidly. With prewetted aggregates, microcracking does not occur, and only a very slow abrasion of the aggregates is observed. Porosity remains high and no ponding excess occurs. The discussion of these results shows that it is the way of the wetting and the initial water content which determine the breakdown mechanism, and therefore, the behaviour of the aggregates submitted to rainfall. ISSN 0341-8162 @1989 by CATENA VERLAG, D-3302 Cremlingen-Destedt, W. Germany 0341 8162/89/5011851/US$ 2.00 + 0.25

CATENA An Inlerdisciplinarv Journal of SOIL SCIENCE

HYDROLOGY

On a 6tudi6 la formation des crofites sous raction de pluies simul~es au laboratoire, en utilisant des 6chantillons constitu+s d'agrbgats calibr+s initialement secs ou satur6s. Des pr+16vements ont 6tb effectu+s au cours de rexp6rimentation afin d'~tudier l'~volution de la teneur en eau et de la distribution de la taille des particules. La g~om+trie de l'espace poral est d+crite sur des lames minces et par porosim6trie au mercure. Dans le cas des agr+gats initialement secs, une microfissuration se produit, la surface se ferme et un exc+s d'eau appara~t rapidement en surface. Avec les agr~gats satur~s, cette microfissuration n'intervient pas et on observe simplement une 16g+re abrasion de la p~riph+rie des agr~gats. La porosit~ reste +levbe et aucun exc~s d'eau n'appara~t durant l'exp+rimentation. La discussion de ces r6sultats montre que le mode de r~humectation et l'+tat hydrique initial d~terminent la nature des m~canismes de d~sagr~gation, et plus g~n~ralement, le comportement des agr~gats soumis fi l'action des pluies.

GEOMORPHOLOGY

Le Bissonnais, Bruand & Jamagne

378

1

Introduction

2. mechanical breakdown due to raindrop impact on aggregates;

Crust formation under raindrop impact is a well known phenomenon in loamy soils, particularly in those rich in silt. It can both prevent seedling emergence and induce runoff and erosion. ELLISON (1945), studying crust development, states that erosion starts with the breakdown of soil aggregates into individual components. Their displacement on the soil surface is due to splash. In an experimental work, M c I N T Y R E (1958) investigated the effect of soil properties on soil splash and mechanisms active in crust formation. More recently, a number of workers have studied aggregate breakdown and rainsplash mechanisms (SAVAT & POESEN 1981, AL D U R R A H & B R A D F O R D 1982, COUSEN & FARRES 1984, FARRES 1987) and crust morphology (CHEN et al. 1980, VALENTIN 1981, O N O F I O K & S I N G E R 1984, B O I F F I N & BRESSON 1987, N O R T O N 1987). B O I F F I N (1984) and BOIFFIN & M O N N I E R (1985), have shown that crust formation on a silty soil results from three successive processes:

3. microcracking resulting from swelling and shrinkage due to successive wet/dry cycles.

The great influence of initial water content on structural stability has also been noted. In a detailed experimental study on aggregate breakdown, LE BISSONNAIS (1988a and b) has shown that the type of breakdown mechanism is closely related both with the initial water content and the wetting procedure of the aggregates. Moreover, each mechanism induces a typical resultant particle size distribution. In this work, our objective is to analyze the relationship between mechanisms of aggregate breakdown, dynamics of crusting, and type of crust structure. These data will allow a better knowledge of the rate of soil crust formation during a rainfall event, and the nature of the particles which can be displaced by runoff.

1. detachment of particles; 2. movement of detached material to the lowest areas;

2

Materials and methods

3. compaction by raindrop impact.

2.1 The total weight and the characteristics of mobilized particles are determined by the conditions and size of the initial clods. Three main mechanisms have been identified by these authors: 1. slaking which results from air compression by water inside pores during wetting; C~AIENA

Soil sample

Clods were collected from 0-25 cm depth in a cultivated silty soil located near Paris, which is classified as a "sol brun lessiv~" (orthic luvisol). Clods were airdried and sieved at 4 mm. The 3 4 mm diameter aggregates composed the sample which is studied. Results of physical and chemical analysis are given in tab.1.

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Experimental Study o f Soil Crusting

<2/zm

2-20/zm

19.6

26.1

379

Grain size distribution C.E.C. 20-50#m 50-200/~m 200-2000/zm meq/100g 46.5

6.2

1.6

O.M. %

pH

1.97

6.2

10.1

CaCO3 %

0.3

Tab. 1: Characteristics of the soil. 14cm

pie s t i-

rigid plastic support with h o l e s

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Fig. 1: Schematic representation of a plastic ring filled with aggregates and sand.

2.2 2.2.1

Experimental procedure

of the kinetic energy of equivalent natural rain, and the drop size distribution was near that of natural rain.

Plot description

The 3 4 mm aggregates were put, for a part, in 14 cm diameter rings and, for another, in Kubiena boxes. The aggregate layer was 3 cm thick, with one 1 cm coarse sand layer at the bottom to allow drainage of infiltrated water (fig.l). In one case, air-dry (AD) aggregates were used. In the other, they were prewetted until saturation (PW), by capillarity under vacuum, using distilled water.

2.2.2

The rings and Kubiena boxes were placed together under the rainfall simulator. They were taken out for morphological observation and particle and pore size analysis after 5, 10, 20, 40 and 90 min for the AD aggregates (corresponding with 1.7, 3.4, 7, 14 and 30 mm of rainfall respectively), and only after 40 and 90 min for the PW aggregates.

2.3

Rainfall simulation

Crust structure and aggregate breakdown analysis

The rainfall simulator consisted of a 1 m 2 constant head tank (FARRES 1987), 2.3.1 Surface observation with silicon capillaries at the density of 5.6/dm 2. Drops from the capillaries fell After progressive drying the surface of 6 m through a randomizing screen to the the plots was examined with a binocular experimental plots below. microscope at different magnifications, in The rainfall intensity was 20 mm/h. order to describe the evolution of strucThe simulated rain had more than 80% ture and roughness. CA'lENA

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2.3.2

Le Bissonnais, Bruand & Jamagne

Thin sections

P = --27cosO/D

The crusts obtained in the Kubiena boxes were progressively air-dried, then dried at 40°C for 24 hours and impregnated by a polyester resin diluted with 30% in volume styrene monomer. Thin sections were made to allow the investigation of the vertical organization of the crust.

2.3.3

Particles size analysis

At each state of crust development, soil samples were taken from the crust (05 mm) and from underneath (5-20 ram), in order to study the particle size distribution evolution. Five replications of 5 g each were taken at each state, immediately after the end of rainfall. We used a procedure previously described (LE BISSONNAIS 1988b) which consists of:

where P is the applied pressure, 7 and ® are the surface tension of mercury and its contact angle on soil material respectively, and D the diameter of the smallest pores intruded by mercury at pressure P. Mercury intrusion was made using a Micromeretics 9320 porosimeter which operates up to a maximum pressure of 200 MPa. Values for ? and ® were taken to be equal to 0.484 N m 1 and 130 ° respectively (FIES 1984). With these values, the equipment allows to describe pore size distribution for pores with an equivalent pore diameter between 300/~m and 6x 10 -3 /~m.

1. Immersion of the sample in ethanol and sieving at 0.1 mm; 2. drying the fraction 0.1 mm at 105°C;

higher

than

3. dry-sieving of this part at 0.2, 0.5, 1 and 2 m m without stirring. These processes permit to obtain a 6 class particle size distribution. Moreover, water content of the aggregates was determined for each sampling.

2.3.4

Mercury porosimetry

This method involves measurement of the pressure required to force mercury into the pores of a dry sample and the volume of intruded mercury at each pressure ( L A W R E N C E 1977). Assuming cylindrical pores, the relationship between pore diameter and applied pressure is given by equation: (AIENA

Fig. 2: Cross section o f a crust included in the epoxy resin. Samples were progressively air-dried, then oven-dried at 105°C during 12 hours. Fragments of crust were envelopped by a viscous epoxy resin so as to envelop the fragment except the crust surface (fig.2). This method also allows to create a small volume of 100 to 300 m m 3 under the crust which is occupied by air. Mercury can only penetrate into this volume when the applied pressure allows the mercury to pass through the upper part of the crust.

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Experimental Study o£ Soil Crusting

381

0 I

. . . . .

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,

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P h o t o 1: Binocular observations of the crust surface and the thin sections for different states of evolution with initially air-dried aggregates: a & f: initial aggregates; b & g: after 1.7 m m rain; c & h: after 7 m m rain; d & i: after 14 m m rain; e & j : after 30 m m rain.

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382

0

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Photo 2: Binocular observations of the crust surface and the thin sections for d!fferent states of evolution with initially prewetted aggregates: a & d: initial aggregates; b & e: after 14 mm rain; c & f: after 30 mm rain.

3 3.1

ResuLts Crust surface description

The surface shows a quick evolution with AD aggregates (photo 1). Until 5 min after rainfall beginning, aggregates appear as isolated fragments (photo lb). At this time, less than 2 m m rain has been applied to the aggregates and breakdown

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occurs without displacement of particles. At the following stage (7 m m rain), the interaggregates space is totaly occupied by the dislodged microaggregates. The size of the breakdown products appears to be unchanged compared to the previous stage (photo lc). The appearance of water on the crust surface (14 m m rain) corresponds to the individualization of

An Interdisciplinary

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SCIENCE

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Experimental Study of Soil Crusting finer particles than previously (photo ld). Finally, after 30 mm rain, the amount of fine particles has increased and the surface becomes very smooth (photo le). With the PW aggregates, 14 mm rain are required to note an evolution of the crust (photo 2b). The aggregates remain individualized but they become blunted. Moreover, pores between aggregates are partially clogged by fine particles. At the end of the experiment (90 min; 30 mm rain), there is no excess of water at the crust surface, which is similar to the crust at 14 ram, except for a higher ratio of clogged pores (photo 2c).

3.2

Thin sections observation

With initial AD aggregates, after 1.7 mm, only the two superficial layers of aggregates are affected by rewetting: a network of cracks appears. The aggregates of the top layer are partly joined (photo lg). After 7 mm of rain, the cracking affects all the aggregates. The crust is still discontinuous (photo l h). At the third stage (14 mm), the crust becomes continuous and well formed (4~ 5 mm thick), but it remains a structural crust without elementary components separation (photo li). In the last state (30 mm rain), we can observe the beginning of the separation of elementary components and their deposition in the micro-depressions (photo l j). In the case of PW aggregates, after 14 mm of rain, initial aggregates are still clearly distinguished (photo 2e), but bonds with a high silt content can be observed between the aggregates. After 30 mm rain, the organization is the same but the bonds are more numerous than previously (photo 2f). CAq ENA

383

3.3

Size of mobilized particles

Fig.3a shows the evolution of size distribution of particles mobilized in the crust with AD aggregates. The fraction of particles greater than 2 mm decreases drastically during the first phase, and the size of produced particles is between 200 pm and 1 mm. During the following phases, the percentage of this size class decreases for the benefit of the class smaller than 100 ktm. Under the crust, after 1.7 mm rain, there is no significative evolution (fig.3b). After 7 ram, the particle size distribution is the same as after 3.4 mm for the crust, but then, we do not observe the increase of the finest class (fig.3a and 3b). With the PW aggregates, the evolution of particle size distribution is very limited (fig.3c). The ratio of particles larger than 2 mm remains higher than 75% during the whole experiment. The only significant evolution is the decrease of particles larger than 2 mm for the benefit of the class smaller than 100 pm. Under the crust, the evolution is still more limited (fig.3d). 3.4

Evolution of water content

The fig.4a shows that, with AD aggregates, water content increases until 39 cc/100 g. This value is reached between 7 and 14 mm rain. With PW aggregates, the initial water content is about 30 cc/100 g and it does not change during the experiment (fig.4b). 3.5

Size of the largest pores of the crust

After 30 mm rain, the two types of crust were studied with five replications. With AD aggregates, the mercury passes through the crust when the pressure

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CATENA--An Interdisciplinary Journal of SOIL SCIENCE

HYDROLOGY-~SIEOMORPHOLO(}y

Experimental Study o f Soil Crusting, . . . . . . . .

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CAEENA

A n Interdisciplinary Journal o f S O I L S C I E N C E

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Le Bissonnais, Bruand & Jamagne

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CATENA An

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of SOIL SCIENCE HYDROLOGY GEOMORPHOLOGY

Experimental Study o f Soil Crusting

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Fig.

Initial aggregates Air-dried aggregates Prewetted aggregates

Total pore volume cc/g

D value for the maximum of the derivative curve /~m

0.202 0.211 0.200

2.8 2.2 2.5

Tab. 2: Characteristic values of the cumulative pore volume curve (mercury porosime-

try).

CATENA An Interdisciplinary Journal of SOIL SCIENCE

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388

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Fig. 6: Cumulative pore volume curve obtained with initial aggregates ( + ) and aggregates from under the crust obtained after 30 mm rain with initially air-dried aggregates ( x ) and initially prewetted aggregates ( [ ] ) . reaches a value wich corresponds to a mean pore diameter of 10 #m (s.d. = 3 /am). With the PW aggregates, the mean value of pore diameter is 25 /am (s.d. = 5/am). 3.6

Pore size description of aggregates located under the crust

The results obtained with the aggregates sampled under the two types of crust after 30 m m of rain, are presented by fig.6. The total pore volume is a little higher with A D aggregates than with initial ag-

gregates or PW aggregates (tab.2). Between these two last results, there is no significant difference. The diameter values coresponding to the maximum of the derivative curve are not significantly different in the three cases (fig.6, tab.2). We only note that the volume of mercury intruded into the aggregates for the pores greater than 4 #m in diameter, is higher with A D aggregates than with initial or PW aggregates.

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Experimental Study of Soil Crusting 4

Discussion and conclusion

4.1

Crust development with initially air-dried aggregates

Three different successive stages of crust evolution during the studied sequence can be distinguished: a - - The f r s t stage corresponds to the wetting of the upper layer of aggregates and leads 1.7 m m rain. These aggregates are micro-cracked (photo lg), and the size of mobilized particles is intermediate (70% between 200 ~tm and 2 ram) (fig.3). We can compare this size distribution with the mesh size of the network of microcracks which is the same. The upper aggregates are ponctually bonded together, but a high porosity is maintained between them, and particles are not displaced. Water can infiltrate into the soil. b - - During the second stage, between 1.7 and 7 m m of rainfall, the upper layer of aggregates is saturated but no ponding occurs on the surface (photo l c). Particles mobilized during the previous stage, are moved by raindrop impact and they progressively fill the interaggregate pores. About 60% of the mobilized particles remain between 0.2 m m and 2 m m (fig.3a). Nevertheless, we note that the importance of particles <0.1 m m increases (30% of <0.1 m m after 7 m m rain). All these particles form a structural crust ( B O I F F I N 1984). Under the crust, aggregates are progressively wetted between 1.7 and 3.4 m m rain (fig.4a) and are completely microcracked after 7 m m rain (photo lh). At this time, the size distribution of CA[ENA

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389

particles mobilized is the same as after 3.4 m m of rainfall in the crust (fig.3a and b). c - - The third stage begins with the start of ponding after 7 mm rain. The displacement and mechanical breakdown of mobilized particles have closed the surface (photo ld). The infiltrability of the crust becomes lower than rainfall intensity. During this stage, there are no aggregates >1 mm in the crust and the importance of the finest class (<100 #m) continues to increase (fig.3a). At the end of this stage (30 m m rain), a depositional crust appears in microdepressions, due to removal and dispersion of particles into the surface water sheet (photo l j). The crust is about 5 m m thick and the roughness is very low (<2 mm). Mercury porosimetry shows that the size of the largest pores in this crust is near l0 /~m, i.e. a little higher than for the initial aggregates (fig.5 and 6). Under the crust, the particle size distribution remains the same as after 20 min. (fig.3b). This area is not affected by raindrop impact and the aggregates are not modified because of the protection by the crust. Thin section shows that the only evolution is the microcracking of aggregates which happened during the previous stage (photo l j). The pore volume due to microcracks can be evaluated to be approximately 0.01 cc/g from the results in tab.2, by comparing the total pore volumes of initial and A D aggregates. Moreover, it is the presence of microcracks which allows the mercury to penetrate more easily into the pores

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teraggregate pores are remaining free of The water content, whose evolu- particles. The material, which bonds the tion is similar inside and under the aggregates, seems to have a higher concrust, reaches its maximal value (38 tent of silt grains than the aggregates cc/100g) between 7 and 14 mm of (photo 2). This might also explain why rainfall (rigA). This value is higher mercury penetration in these areas octhan the water content of initial PW curs already at pressures equivalent to aggregates. In the case of the aggre- pore diameters of 20-30#m. There is no difference in pore size disgates which come from under the tribution between initial aggregates and crust after 30 mm rain, this differPW aggregates in the final state (fig.6). ence is about 0.09 cc/g, i.e. much This is consistent with the stability of higher than the pore volume atwater content during the experiments. tributed to the microcracks (0.01 cc/g). In this last case, pore volume was determined after drying. The 4.3 Aggregate breakdown mechanisms shrinkage of aggregates during airand crust development drying, may have caused a considerable reduction of microcrack vol- The two very different types of surface evolution can be explained by the nature ume. of the mechanisms of aggregate breakdown. These mechanisms are determined 4.2 Crust development with initially by the opportunity to trap air inside the prewetted aggregates aggregates during wetting. Breakdown by air trapping, i.e. slakIt is difficult to distinguish different stages of crust development because of ing, can be very drastic if the aggregates the very slow evolution during the ex- are dry and quickly rewetted. A moderperiment. Aggregates seem to be unbro- ate breakdown due to partial air trapping ken and the roughness does not change can also occur at each rewetting phase. (photo 2). Thin sections show that small The result is microcracking. This type particles accumulate between aggregates, of breakdown is closely related with the just under the upper layer of aggregates wetting kinetics and pore size distribu(photo 2e). The size of these particles, tion but also with the swelling properwhich increase slowly in number during ties of the material (LE BISSONNAIS the experiment, is smaller than 0.1 mm 1988a). In our experiment, air trapping oc(fig.3c). The other classes of particles mobilized (between 0.1 mm and 1 ram) are curs during rainfall with AD aggregates. weakly present. Nevertheless, there ap- With PW aggregates, wetting is perpears a few percent of particles 1-2 mm formed under vacuum before the rainin size, which result from the abrasion fall, and no air can be trapped before or by raindrop impact of the smallest ag- during the rainfall. With an atmospheric gregates. It is noticed that water content pressure rewetting, the aggregates would (29 cc/100 g) does not change during the have been microcracked before the beginning of rainfall and the crust develexperiment (rigA). In the final state (30 mm rain), the opment would have been similar in the surface is not totally crusted, some in- two cases. of the aggregates.

CA'lENA

An Inlerdisciplinary Journal o f SOIL SCIENCE

t~IYDROLOGY (~EOMORPHOLOGY

Experimental Study o£ Soil Crusting This point can explain the divergence between our results and those obtained by C O U S E N & FARRES (1984). The increase of instability with the water content pointed out by these authors could be due to a breakdown process during wetting, which is realized at atmospheric pressure. On the contrary, GOVERS et al. (1987), found that runoff erosion appears is more on a dry soil than on a wetted one. These authors explain this result by the slaking of aggregates and the production of small particles easely displaced by runoff. Our procedure o f wetting under vacuum, which does not occur under field conditions, allows to discuss the influence of initial water content changes on aggregate stability and crusting. Results show the necessity to consider the moisture content of the soil before a rainfall event, to determine the risk of runoff and erosion. Indeed, the behaviour of the soil surface can be very variable for the same soil and the same rainfall event. This was recently observed by B O I F F I N et al. (1988), in a study of erosion realized in the "Pays de Caux" (France), where crusting is the main cause of runoff. Thus, an index of erodibility for one soil cannot be defined as a permanent characteristic of this soil. To be able to make some prediction on the risk of erosion for a rainfall event, it would be necessary to take into account the climatic and agricultural history. Acknowledgements The authors like to thank R C O U R T E M A N C H E , Ch. LE LAY and B. REN A U X (SESCPF, I N R A Orleans) for their help in performing of the experiments. CAI'ENA An Interdisciplinary Journal of SOIL SCIENCE

391

References AL-DURRAH, M. & BRADFORD, J.M. (1982): The mechanism of raindrop splash on soil surfaces. Soil Sci. Soc. Am. J. 46, 1086-1090. BOIFFIN, J. (1984): La d~gradation structurale des couches superficielles du sol sous Faction des pluies. Th~se Docteur Ing~nieur, Paris INA-PG, 320 p.

BOIFFIN, J. & BRESSON, L.M. (1987): Dynamique de formation des crofites superficielles: apport de l'analyse microscopique. In: N. Fedoroff, L.M. Bresson et M.A. Courty (~d.), Micromorphologie des sols. Actes dc la VII R~union Internationale de Micromorphologie des sols. Paris, Juillet 1985. AFES, 393 399. BOIFFIN, J. & MONNIER, G. (1985): Infiltration rate as affected by soil surface crusting caused by rainfall. Flanders Research Center for Soil Erosion and Soil Conservation. Assessment of soil surface sealing and crusting. Ghcnk 374 p. BOIFFIN, J., PAPY, F. & EIMBERCK, M. (1988): Influence des syst~mes de culture sur les risques d'~rosion par ruissellement concentr& 1. Analyse des conditions de d~clenchement de l'~rosion. Agronomie 8(8), 663-673. CHEN, Y., TARCHITZKY, J.T., BROUWER, J., MORIN, J. & BANIN, A. (1980): Scanning electron microscope observations of soil crusts and their information. Soil Sci. 130, 49 55. COUSEN, S.M. & FARRES, P.J. (1984): the role of moisture content in the stability of soil aggregates from a temperate silty soil to raindrop impact. CATENA 11, 313-320. ELLISON, W.D. (1945): Some effects of raindrops and surface flow on soil erosion and infiltration. Trans. Am. Geophys. Union 26, 415°429.

FARRES, P.J. (1987): The dynamics of rainsplash erosion and the role of soil aggregate stability. CATENA 14, 119 130. FIES, J.C. (1984): Analyse de la r~partition du volume des pores dans les assemblages argile-squelettes: comparaison entre un modble d'espace poral textural et les donn~es fourniers par la porosim&rie au mercure. Agronomie 4(9), 89!-899. GOVERS, G., EVERAERT, W., POESEN, J., RAUWS, G. & DE PLOEY, J. (1987): Susceptibilit6 d'un sol limoneux fi l'6rosion par rigole: Essais dans le grand canal de Caen. Bull. du Centre de gbomorphologie de Caen - - CNRS no. 33, 83-106.

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LAWRENCE, G.P. (1977): Measurement of pores sizes in fine textured soils: a review of existing techniques. J. Soil Science 28, 527-540. LE BISSONNAIS, Y. (1988a): Analyse de mbcanismes de d6sagr~gation et de la mobilisation des particules de terre sous Faction des pluies. Th~se Doc. Univ. Orleans, 225 p. LE BISSONNAIS, Y. (1988b): Comportement d'agr6gats terreux soumis ~. raction de l'eau: analyse des m+canismes de d~sagr~gation. Agronomie 8(10), 87-93. NORTON, L.D. (1987): Micromorphological study of surface seals developed under simulated rainfall, Geoderma 40, 127-140. MelNTYRE, D.S. (1958): Soil splash and the formation of surface crusts by raindrop impact. Soil Science 85, 261-266.

ONOFIOK, O. & SINGER, M.J. (1984): Scanning electron microscope studies of surface crusts formed by simulated rainfall. Soil Sci. Soc. Am. J. 48, 1137 1143. SAVAT, J. & POESEN, J. (1981): Detachment and transportation of loose sediments by raindrop splash. Part I. The calculation of absolute data on detachability and transportability. CATENA 8, 1-17. VALENTIN, C. (1981): Organisations pelliculaires superficielles de quelques sols de r~gion subd~sertique. Th~se 3 eme cycle, Universit~ Paris 7, 213 p.

Address of authors: Yves Le Bissonnais, Ary Bruand, Marcel Jamagne Centre de Recherches d'Orl~ans - - INRA Service d'Etude des sols et de la Carte P6dologique de France Ardon 45160 Olivet France

CATENA

An Interdisciplinary Journal of SOIL SCIENCE

HYDROLOGY GEOMORPHOLOGY