From water to tillage erosion dominated landform evolution

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Geomorphology 72 (

From water to tillage erosion dominated landform evolution

K. Van Oost a,c,*, W. Van Muysen a, G. Govers a, J. Deckers b, T.A. Quine c

aPhysical and Regional Geography Research Group, K.U.Leuven, BelgiumbInstitute for Land and Water Management, K.U.Leuven, Belgium

cHydrology and Earth Surface Processes Research Group, University of Exeter, UK

Received 30 March 2004; received in revised form 9 May 2005; accepted 17 May 2005

Available online 8 August 2005

Abstract

While water and wind erosion are still considered to be the dominant soil erosion processes on agricultural land, there is

growing recognition that tillage erosion plays an important role in the redistribution of soil on agricultural land. In this study, we

examined soil redistribution rates and patterns for an agricultural field in the Belgian loess belt. 137Cs derived soil erosion rates

have been confronted with historical patterns of soil erosion based on soil profile truncation. This allowed an assessment of

historical and contemporary landform evolution on agricultural land and its interpretation in relation to the dominant

geomorphic process. The results clearly show that an important shift in the relative contribution of tillage and water erosion

to total soil redistribution on agricultural land has occurred during recent decades. Historical soil redistribution is dominated by

high losses on steep midslope positions and concavities as a result of water erosion, leading to landscape incision and

steepening of the topography. In contrast, contemporary soil redistribution is dominated by high losses on convex upperslopes

and infilling of slope and valley concavities as a result of tillage, resulting in topographic flattening. This shift must be attributed

to the increased mechanization of agriculture during recent decades. This study shows that the typical topographical dependency

of soil redistribution processes and their spatial interactions must be accounted for when assessing landform and soil profile

evolution.

D 2005 Published by Elsevier B.V.

Keywords: Landform evolution; Tillage erosion; Soil erosion; SPEROS model; Belgian loess belt; 137Cs

1. Introduction

Soil erosion is mainly studied in relation to soil

degradation and sediment export at spatial and temporal

0169-555X/$ - see front matter D 2005 Published by Elsevier B.V.

doi:10.1016/j.geomorph.2005.05.010

* Corresponding author. Physical and Regional Geography Re-

search Group, Redingenstraat 16, B-3000 Leuven, Belgium. Tel.:

+32 16 32 64 07; fax: +32 16 32 64 00.

E-mail address: [email protected] (K. Van Oost).

scales of relevance to land managers (Lal, 2001). While

several studies have assessed the topographical con-

trols on water erosion processes (e.g.Moore and Burch,

1986; Govers, 1991; Moore and Wilson, 1992;), rela-

tively little attention has been given to the influence of

erosion processes on landform evolution on agricultur-

al land (Quine et al., 1997). This reflects the short-term

nature of process studies, which hampers the extrapo-

lation of results to larger spatial and temporal scales.

2005) 193–203

K. Van Oost et al. / Geomorphology 72 (2005) 193–203194

Water and wind erosion are still considered to be the

dominant soil erosion processes on agricultural land,

but there is growing recognition that tillage erosion

plays an important role in the redistribution of soil on

agricultural land (Lindstrom et al., 1992; Govers et al.,

1994; Lobb et al., 1995).With its distinct spatial pattern

of erosion at convexities and deposition at concavities

(or hollows), tillage erosion redistributes soil in

amounts that often dwarf the effect of water erosion

on rolling arable land (Govers et al., 1996). The depen-

dency on topography of water erosion is totally differ-

ent: water erosion is maximal on steep slopes and

where water concentrates (i.e. hollows) (Moore and

Burch, 1986; Desmet and Govers, 1997). The spatial

signatures of water and tillage erosion and landform

evolution are therefore contrasting.

Although agricultural soils have been tilled since the

dawn of agriculture, high tillage erosion rates only oc-

curred after the introduction of mechanized agriculture in

the 1950s. Mechanized agriculture considerably in-

creased tracking power, tillage speed and depth and con-

sequently soil translocation and erosion by tillage (e.g.

Van Oost et al., 2000). We therefore hypothesize that

landform evolution on agricultural land has changed

with the introduction of mechanized agriculture.

In order to asses landform evolution, representative

longer-term data on soil erosion (and deposition) rates

and patterns are needed: while topographical changes

are not always clearly identifiable on a short time scale,

they may be more easily determined when a medium to

long time scale is considered. Depth to benchmark

layers in the soil profile have been frequently used

for historical (i.e. several centuries) erosion assessment

(e.g. Lowrance et al., 1988; Phillips et al., 1999, Jan-

kauskas and Fullen, 2002). However, other methods

are required to estimate contemporary (i.e. several

decades) soil erosion. One of these methods is the137Cs technique, which can be used to estimate me-

dium-term (35–45 years) soil redistribution rates and

patterns and has now been employed in erosion inves-

tigations in a wide range of environments (e.g. Ritchie

and McHenry, 1990; Quine et al., 1997).

This paper reports a study initiated to relate cae-

sium-derived soil erosion rates and patterns over a 43

year period to observed spatial variations in soil pro-

file characteristics. Specific objectives were: (a) to

apply the 137Cs technique to assess contemporary

soil erosion and deposition patterns and rates for a

field under long standing cultivation in the Belgian

loess belt; (b) to investigate the spatial variation in soil

profile composition for this study site in the light of

the historical erosion processes at work; (c) to con-

front the contemporary (137Cs-derived) soil redistribu-

tion patterns with the observed historical (soil profile

derived) soil erosion. Finally, the consequences for

contemporary landform and soil profile evolution on

agricultural land are discussed.

2. Materials and methods

2.1. Study site

A study site was selected in the loam belt of central

Belgium, located ~8 km SW of Leuven in the muni-

cipality of Leefdaal (50850V N, 4835V E). The main

local soil types are Luvisols, Cambisols and Regosols

(FAO, 1998) which have developed in loess deposits.

The study site consists of a hillslope of ~3.6 ha, with

the main slope oriented towards the SE. Archaeolo-

gical findings indicate that the first cultivation of the

area dates back ~3000 years (Bossuyt et al., 1999).

Present day land use consists of a rotation of cereals

with potatoes, maize and sugarbeet, a crop rotation

which is typical in the Belgian loess belt. Annual

precipitation varies between 700–850 mm and is dis-

tributed equally all over the year.

The study site consists of a convex–concave slope

with a sharp concavity near the thalweg (Fig. 1).

While no plan-curvature is apparent on the western

side of the field, a concave hollow is visible on the

eastern side. A grass strip, bordered by a long stan-

ding forest on the southern edge, delineates the field.

Slope gradients up to 0.15 mm�1 on the steepest parts

of the area occur, while slope lengths are within the

50–200 m range. A detailed topographical survey

(with a 10*10 m grid size) was carried out using an

automatic theodolite to construct a digital elevation

model.

2.2. 137Cs sampling

Soil samples for 137Cs inventory assessment were

taken during August 1997. A cylindrical tube (internal

diameter 7.6 cm) was drilled into the soil using a

percussion coring device until a depth of 60 cm was

Fig. 1. Field site topography (contour interval 1 m) with indication

of sampling points for 137Cs inventory (symbol R ) and soil profile

(symbol +) assessment. Dark shaded area represents grass strip.

K. Van Oost et al. / Geomorphology 72 (2005) 193–203 195

reached. A total of 36 soil samples were taken along 5

transects, spaced 20 m apart and parallel to the direc-

tion of tillage. Samples were air dried, ground and a

~1.1 kg subsample of the b2 mm fraction analysed for

determination of the 137Cs concentration by gamma

spectrometry at 662 keV using a Ge detector at the

Institute of Nuclear and Radiation Physics at the

Katholieke Universiteit Leuven. Counting times were

on average 43601 s (standard deviation=11200 s;

n =36), providing a measurement precision of F8%.

Based on the total sample weight and the internal

diameter of the cylinder tube (7.6 cm), 137Cs concen-

trations data (Bq g�1) were converted to 137Cs inven-

tories (Bq m�2). Reference 137Cs samples were taken

on non-eroding plateau positions, leading to a refer-

ence value of 3290 Bq m�2 (standard deviation=150

Bq m�2, n =5) in 1997.

2.3. 137Cs conversion

The 137Cs data may be used directly to examine

qualitative patterns of medium-term soil redistribution

by calculating 137Cs residuals:

Csres;x ¼ Csx � Csrefð Þ=Csref ð1Þ

where Csres,x is the137Cs residual at location x, Csx is

the 137Cs inventory at location x and Csref is the

reference 137Cs inventory (3290 Bq m�2). Negative

residuals indicate erosion, and positive residuals indi-

cate aggradation. The residuals provide direct, unbi-

ased evidence of total soil redistribution.

However, conversion models are needed to convert

the 137Cs residuals into quantitative estimates of soil

redistribution and to assess the relative contribution of

the different soil redistribution processes. A spatially

distributed 137Cs conversion model (SPEROS; Van

Oost et al., 2003) was used to convert the 137Cs

inventories into rates and patterns of soil redistribu-

tion. The model combines a 137Cs mass-balance model

(Quine, 1995), describing the accumulation and deple-

tion of 137Cs at one point in the landscape, with

process-based water and tillage erosion models in a

spatial context. The model exploits the fundamentally

different dependency on topography of water and till-

age erosion to establish their relative contribution in

the total soil redistribution (Govers et al., 1996).137Cs fallout resulting from the nuclear accident in

Chernobyl was derived from direct measurement in

the vicinity of the study area (Vanden Berghe and

Gulinck, 1987). Interpolation of their data resulted

in an estimate of the Chernobyl 137Cs fallout of 800

Bq m�2 for the study area. Parameter values for the

conversion model were the same as those proposed by

Van Oost et al. (2003). The parameter values for the

water erosion model were obtained from local field

studies (Govers, 1991; Desmet and Govers, 1997)

where the study field site is located. We assumed a

constant tillage depth of 0.25 m. As no detailed

information on tillage directions during the last four

decades was available, we assumed that soil translo-

cation by tillage occurred in the direction of the

steepest slope, which is also the present-day tillage

direction.

The conversion model was then applied without a

priori assumptions about the intensity of water or

tillage soil erosion. An analysis was performed to

explore the water and tillage model parameters at

which the model is in close agreement with the ob-

served 137Cs inventories (see Van Oost et al., 2003 for

more details). The goodness of fit measure employed

here was the model efficiency (MEF):

MEF ¼ 1� r2=r2obs ð2Þ

Fig. 2. Typical soil profiles, developed in loess soils under (a)

deciduous forest and (b) under cultivation (Langohr and Vermeire,

1982). On non-eroding sites, a typical soil profile consists of a ~20

cm thick Ao and A1 horizon (~30 cm thick plough layer, Ap horizon,

in the case of cultivation), overlaying a lighter coloured eluvial

horizon (E), followed by the argillic B horizon (Bt horizon) between

~45 and 120 cm depth. The decalcified C1 material (~120–240 cm)

and the calcareous loess (C2 horizon) is situated below.


where r2 is the variance of the residuals between

measured and simulated 137Cs inventories and robs2 is

the variance of the observed inventories. The MEF

value generates a coefficient of determination that

indicates how well the line of perfect agreement

describes the relation between predicted and observed

values. In total, 5000 parameter sets for the water and

tillage erosion model were generated and the conver-

sion model was run to compare the observed and

predicted 137Cs inventories for each parameter set.

Next, a procedure based on the Generalized Likeli-

hood Uncertainty Estimation approach is implemen-

ted to estimate the uncertainty associated with model

calibration (Beven and Freer, 2001). The degree of

uncertainty surrounding the model output is based on

the 25th and 75th percentile simulation limits while

estimates of the field-mean intensity of both water

and tillage erosion are based on the median model

simulation.

2.4. Soil profile description

Information on soil profile truncation was col-

lected by means of an augering campaign. The

study area was surveyed during the winter of

1997–1998. Augering was done at 48 positions

along a series of five transects, parallel to the tillage

direction and at ~20 m intervals (Fig. 1). Augering

was carried out to 3 m depth and the depth of each

diagnostic horizon was recorded. At locations where

colluvium was found below 1 m, auger depth was

limited to 1.5 m.

Historical soil erosion and deposition rates and

patterns may be obtained from soil profile informa-

tion. Fig. 2 describes typical non-eroded soil profiles,

developed in loess under longstanding arable land and

under natural conditions. In many cases, soil profiles

under long-standing cultivation have been truncated

by erosion. In loess soils, truncation can be identified

by measuring the depth to the upper level of the

calcareous C2-horizon. The depth at which the C2

horizon is found in uneroded profiles may vary some-

what, depending on landscape position, topography

and hydrology (Dudal, 1955). Generally, a reference

depth of 230– 260 cm for uneroded profiles is used in

the loess belt of Belgium (Goossens, 1987; Nachter-

gaele and Poesen, 2002). We used the depth of the C2

horizon to estimate rates and spatial patterns of his-

torical soil erosion. When C2-derived soil erosion was

directly compared with 137Cs data, the data were

interpolated, using a linear interpolation method.

3. Results and discussion

3.1. Long term soil erosion assessment using soil

profile information

The depth to the calcareous loess allows a quanti-

tative estimate of the spatial distribution of historical

erosion. In Fig. 3, the depth to the C2 horizon is

presented. Depth to the calcareous loess decreases

from the upper plateau positions (C2 material at a

depth of 250–300 cm), to the steepest slope positions,

where C2 material is present directly below and even

mixed within the plough (Ap) layer. Further down-

slope, the depth to the C2 increases again and several

-150 -100 -50

X coordinate (m)

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Observed 137Cs Residuals (%)

137Cs derived water erosion (Mg/ha/yr)137Cs derived tillage erosion (Mg/ha/yr)

Depth to C2 horizon (cm)

-150 -100 -50

X coordinate (m)

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100

150

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Colluvial material below Ap

Overburden of colluvial material over C

Fig. 3. Spatial patterns of observed 137Cs residuals, depth to C2 horizon, tillage and water erosion derived from the 137Cs conversion model,

superimposed on a contour map (contour interval 1 m). The depth of the colluvium is not included in the calculations of the depth of the C2

horizon, when an overburden of colluvial material over C1 or C2 horizons occurs.


metres of colluvium are found at the bottom of the

field. This spatial pattern is consistent with water

erosion: erosion rates increase with both slope steep-

ness and length. Soil truncation is also intense in the

eastern hollow, where overland flow concentrates. An

interesting feature is the occurrence of colluvium

(~0.45 m, indicating deposition) that is in direct con-

tact with the C1 or C2 horizons at this location (see

Fig. 3). This observation suggests that important

changes in soil redistribution patterns have occurred,

as sites that were historically dominated by erosion

are now characterized by deposition.

Table 1137Cs-derived field-mean soil redistribution rates

Mean erosion rate

(Mg ha�1 yr�1)

Mean deposition rate

(Mg ha�1 yr�1)

M M

Water 5.5 3.2

Tillage 9.2 9.2

Total 13.0 10.6


3.2. Medium term soil erosion assessment using 137Cs

It is apparent from Fig. 3 that much of the field

experienced 137Cs depletion, and consequently, soil

erosion during the last 43 years. The redistribution

pattern of 137Cs clearly shows that the most intense

erosion occurs on both the upslope convex and mid-

slope positions. At the same time, a sharp increase in137Cs activity occurs on the transition of footslope to

thalweg positions. Positive 137Cs residuals are also

found in the concave hollow at the eastern side of

the field.

Application of the 137Cs conversion procedure, as

described above, resulted in a good fit between the

simulated and observed 137Cs inventories. The simu-

lated 137Cs inventories and associated model uncer-

tainties are plotted against measured 137Cs inventory

(Fig. 4, R2=0.74, n =31, p b0.001). In Fig. 3, the

predicted spatial patterns of water and tillage erosion

are shown. Tillage leads to erosion on convexities or

shoulders and to deposition in concavities or hollows.

Overland flow maximizes erosion in these concavities

and on the steeper slopes. Thus, both water and tillage

erosion contribute to soil redistribution on this field.

Water erosion is the predominant erosion process on

midslope positions. The maximum zone of 137Cs

Fig. 4. Simulated versus observed 137Cs inventories. The er

depletion (Fig. 3) on the convex shoulder is typical

of tillage erosion. However, infilling of the eastern

hollow due to tillage is partially compensated by

water erosion. Eroded material from both processes

is transported to, and deposited in, the main hollow.

Tillage only redistributes soils within fields, while

water erosion exports sediment from the field. We

estimate that ~82% of the eroded sediment is re-

deposited in the same field while ~18% is exported

by water erosion. In Table 1, water and tillage rates,

derived from the 137Cs measurements, are compared.

Here, the difference in magnitude between water and

tillage erosion becomes apparent, indicating that till-

age erosion was the dominant soil redistribution pro-

cess during the last four decades: the estimated water

erosion rate equals ~6 Mg ha�1 yr�1 while the tillage

erosion rate is ~9 Mg ha�1 yr�1.

ror bars represent the 25th and 75th simulation limits.


The erosion rates accord with regional erosion

estimates and experiments: Van Rompaey (2001)

reported an average water erosion rate of 4.6 Mg

ha�1 yr�1, while Van Oost et al. (2000) obtained

average water and tillage erosion rate of 9.1 and 8.5

Mg ha�1 yr�1, respectively, for the loam belt of

central Belgium. The tillage transport coefficient as

defined by Govers et al. (1994), which is a measure

for the erosivity of a series of tillage operations,

derived from the conversion model equals 524 kg

m�1 yr�1. This is very similar to the tillage transport

coefficients reported in other 137Cs studies (values

range between 350 and 550 kg m�1 yr�1; Govers et

al., 1996; Quine et al., 1994; Van Oost et al., 2003).

These values are lower than the present day coeffi-

cients derived from tillage erosion experiments, which

range between 500 and 800 kg m�1 yr�1 (Van Muy-

sen et al., 2002; Van Oost et al., 2000). The 137Cs

derived tillage transport coefficients, however, are

strongly influenced by past as well as current practice,

as they represent a period in excess of four decades.

3.3. Comparison of historical and contemporary soil

redistribution

Changes in the relative contribution of water and

tillage erosion in soil redistribution are assessed by

comparing their contemporary spatial patterns, de-

rived from the 137Cs conversion, with the patterns of

historical soil erosion, based on soil profile truncation.

The results indicate that the historical soil redistribu-

tion, at a time scale of a few centuries, is dominated

by water erosion. High values of soil profile trunca-

tion are found on steep slopes or where water con-

centrates. This is supported by the significant, positive

relationship between soil truncation and 137Cs-derived

water erosion (Fig. 5, Table 2). In contrast, a negative

relationship between soil truncation and 137Cs-derived

tillage erosion is found (Fig. 5, Table 2). This implies

that tillage leads to deposition in locations where

historical soil erosion rates are high and vice versa.

Consequently, these results suggest that tillage erosion

did not contribute significantly to the long-term soil

redistribution on this field.

The historical soil redistribution pattern is incon-

sistent with contemporary soil redistribution derived

from the 137Cs conversion. Present-day erosion rates

are highest on the convex upslope positions where

relatively uneroded soil profiles occur. In addition to

the deposition in the main thalweg, accumulation of

soil material is nowadays also occurring in the small

concavity on the slope, where a thin layer of colluvial

material is found on top of strongly truncated soils

(Fig. 2). This is because contemporary landform evo-

lution is dominated by tillage erosion. Based on the137Cs conversion, we estimate that ~70% of the total

soil redistribution must be attributed to tillage erosion.

The dominance of tillage erosion in the total soil

redistribution found here is supported by other studies

(e.g. Govers et al., 1996; Lobb et al., 1995; Montgo-

mery et al., 1997; Quine et al., 1997).

The analysis above indicates clearly that an impor-

tant shift in the relative contribution of water and tillage

erosion processes to total soil redistribution has

occured. This is strongly supported by the fact that

soil profile truncation is not related to 137Cs residuals

(Table 2). Although tillage operations have always

been carried out since cultivation started and have, at

least to some extent, caused tillage erosion, water

erosion can be considered to be the primary cause of

the present day observed variation in soil profile com-

position. It is only since mechanization and more in-

tensive cropping systems were introduced during the

20th century that tillage erosion became more impor-

tant. Tillage tools operated at shallow depths and

speeds (eg. hoe, simple turning plough, animal-po-

wered tools) are characterized by a relatively low ero-

sivity. Tillage transport coefficients derived from

experiments conducted in the beginning of the mech-

anization (eg. Mech and Free, 1942) or recent experi-

ments conducted in developing countries using animal

powered equipment (e.g. Nyssen et al., 2000) range

between 50–300 kg m�1 yr�1. With increased mech-

anization and power availability, tillage is carried out

deeper and faster, leading to increased tillage erosivity

(VanMuysen et al., 2002). Present-day estimates of the

tillage transport coefficient under mechanized agricul-

ture in intensive, dryland cropping systems range be-

tween 500 and 800 kg m�1 yr�1 (Govers et al., 1994;

Lindstrom et al., 1992; Van Muysen et al., 2000, 2002;

Lobb and Kachanoski, 1999; Van Oost et al., 2000).

Consequently, tillage erosion intensity increased two-

to threefold during the last 5 decades.

It should be noted that soil loss due to root crop

harvesting, especially in mechanized agricultural sys-

tems, may further increase erosion rates. However,

Fig. 5. Historical soil erosion versus water and tillage erosion. Historical soil erosion is subdivided in four classes. The error bars represent the

scatter in water and tillage erosion estimates (1 standard deviation). Negative values indicate erosion, positive values deposition.


this paper focuses on landform evolution and there-

fore on the spatial variability of soil redistribution

processes. It is reasonable to assume that soil losses

due to crop harvesting are spatially uniform and it is

therefore unlikely that this process will contribute

substantially to the observed spatial differences in

soil truncation and 137Cs inventories.

3.4. Implications

The foregoing discussion has provided better

insights into contemporary landform evolution for

the studied site. Soil translocation by tillage produces

maximum erosion on convex slope positions, causing

a reduction in slope angles, and an infilling of con-

Table 2

Spearman correlation coefficients of historical erosion (based on

soil truncation) with contemporary erosion (based on 137Cs-resi-

duals) and water and tillage erosion (derived from 137Cs conversion)

137Cs residual Water Tillage

Soil truncation (n =26) 0.14 0.72 �0.50

0.71 (NS) b0.001 b0.001

Ten sampling points, located in colluvium, were excluded from the

analysis. Values in italics indicate the associated P-value.


cavities or hollows. Over time, this results in a gradual

smoothening of topographical features. In contrast,

water erosion dominated landforms are characterized

by increased incisions in concavities and a gradual

increase in slope angle on convex slope positions. The

contrasting landform evolution expected from water

or tillage dominated soil redistribution is illustrated by

applying the WaTEM (Water and Tillage Erosion

Model; Van Oost et al., 2000) for a period of 200

years on the study site. We used the water and tillage

Fig. 6. Simulated landform evolution under water and tillage dominated soi

simulation. The dotted lines are the contour lines after 200 years of water

erosion rates obtained from the 137Cs conversion and

assumed that they remained constant over the simu-

lation period. We used a time step of one year and

adjusted the topography after every time step. Fig. 6

clearly illustrates the smoothing of the landscape by

tillage processes and the incision by overland flow.

However, it is important to recognize the con-

straints on extrapolation of the results to longer

time-scales. The 137Cs-derived rates are time-specific

averages for the period 1950–2000 and they cannot be

linearly extrapolated into the future. Changes in agri-

cultural practices (e.g. crop rotation, minimal tillage)

may largely affect the sensitivity to both water and

tillage erosion.

Our results have important implications for the

long-term spatial and temporal variations in soil pro-

file characteristics and landform evolution. Studies

have shown that the resistance of different soil hori-

zons may vary significantly. Nachtergaele and Poesen

(2002) reported that the C horizons of a loess-soil are

l erosion. The solid lines are the contour lines at the beginning of the

(left) and tillage (right) erosion.


16 times more erodible than a Bt horizon. Our data

shows that historical water erosion has resulted in the

complete removal of the Ap and Bt horizons in the

concavities and on steep slopes. These locations are

therefore prone to ephemeral gully erosion. With on-

going water erosion, the spatial extent of these erosion

prone areas will further increase with time. However,

this process has changed since the introduction of

mechanized tillage: tillage erosion exposes subsoil

material on convex upperslope positions, which be-

come more susceptible to water erosion. Furthermore,

soil redistribution by tillage delivers topsoil from the

convexities to areas of concentrated overland flow

(concavities). The tillage deposits in the concavities

may reduce water erosion risk by protecting the

C-horizon. Thus, the understanding of landform evo-

lution on agricultural land in the loess belt requires the

integration of water and tillage erosion, taking into

account the changes in soil profile characteristics.

4. Conclusions

137Cs derived soil erosion rates have been con-

fronted with historical patterns of soil erosion based

on soil profile truncation. This allowed us to assess

historical and contemporary landform evolution on

agricultural land and its interpretation in relation to

the dominant geomorphic process. The results clearly

show that an important shift in the relative contribu-

tion of tillage and water erosion to total soil redistri-

bution on agricultural land has occurred during recent

decades. Where the observed spatial variation in depth

to the calcareous loess material can be attributed to the

action of overland flow erosion since cultivation

started ~2000 years ago, tillage erosion has become

the dominant soil erosion process during recent deca-

des. This is due to the increased agricultural mecha-

nization, resulting in increasingly dominant tillage

erosivity of current applied tillage operations. The

shift in the relative importance of erosion processes

has implications for contemporary landform evolu-

tion: while continuing water erosion leads to increased

incisions in concavities and a gradual increase in slope

angle on convex slopes, tillage erosion smoothens the

landscape and reduces slope angles by moving soil

from convexities to concavities. Also, the spatial-tem-

poral evolution of soil properties is affected as sites

where C-horizons were previously exposed are now

undergoing colluviation. Thus, the typical topograph-

ical dependency of both processes and their spatial

interactions must be accounted for when assessing

landform and soil profile evolution.

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