全 文 ：DETERMINING THE VARIABIL ITY
OF SOIL EROD IBIL ITY FOR
EROSION PRED ICTION
Y. Li1 　M. Frielinghaus2 　H.2R. Bork2
( 1 Instit ute of Mountain Hazards and Envi ronment , CA S , Chengdu 　610041 ; Instit ute
f or A pplication of A tomic Energy , CA A S , Beiji ng 　100094)
( 2 Center f or A gricult ural L andscape and L and Use Research , M uncheberg , Germany)
Soil erodibility refers to the susceptibility or resistance of a soil to detachment and
transport by erosion for a particular site. Accurate prediction of soil erosion strongly re2
quires a sufficient understanding of the variability in soil erodibility parameters. This
paper reviews the existing knowledge on these topics and defines research gaps. In the
framework of soil erosion prediction studies it is important to consider soil erodibility at
various temporal and spatial scales. Little research has hitherto been conducted on quan2
titative assessment of spatial variability in soil erodibility and its relation to soil condition
factors at different landscape level. But such information on this aspect is crucial for
quantitatively describing the paths of erosion and to develop solutions or conceptions to
interrupt these paths within the landscape. From this review , it can be concluded that
special attention must be paid to the quantitative assessment of soil erodibility at various
scales up to the catchment scale. The results of such studies should be used to relate
erodibility parameters to soil condition factors that can be measured easily and confident2
ly. Caesium2137 approach would be a reliable method for determining spatial variability
in soil erodibility within the landscape , which has fast , inexpensive and accurate advan2
tages over many classical measuring techniques.
Key words : Soil erodibility , soil erosion , spatial and temporal variability , caesium2137
本文于 1999 年 3 月 19 日收到。
Soil erodibility is a dynamic soil characteristic subject to temporal [1～10 ] and spatial[11～14 ]
variability. Its measurement and estimation have become central in modern erosion prediction by
the process2based erosion models such as CREAMS , WEPP and GU EST[4 ,15～21 ] .
Significant variation in erodibility can pose problems both in erosion model use and for pa2
rameter estimation. If erosion from individual event on different landscape positions is to be pre2
dicted accurately , both model application and parameter estimation require some ability to predict
soil erodibility parameters and the effects of antecedent soil conditions on erodibility in very het2
921　核 农 学 报　1999 ,13 (3) :129～136Acta A gricult urae N ucleatae Sinica
erogeneous landscape. But to date , no currently available erosion model considers variation in
erodibility in this detail. Therefore , it is very urgent to obtain the information necessary to pre2
dict temporal and spatial variation in erodibility by field and laboratory experiments. Special at2
tention must be paid to the quantitative assessment of soil erodibility at various scales up to the
catchment scale. The results of such studies should be used to relate erodibility parameters to soil
condition factors that can be measured easily and confidently. This would allow for quick compar2
isons between soils and prediction of variations in soil erodibility without a complete experimental
study on each soil.
Current research
The variations in soil erodibility with time are increasingly concerned with by soil conserva2
tionists. The variations in erodibility , both within and between years , have been reported to be
related to climate , temperature , rainfall , soil vegetation and management [1 ,4 ,5～7 ,21～30 ] .
Recently , several detailed studies on the temporal variability in erodibility have been conduct2
ed. Alberts et al. [10 ] measured the variations in soil erodibility parameters ( USL E , Ki and Kr)
and runoff between years by rainfall simulator in the field. The results indicated that the varia2
tions between years was highly significant ( P < 0101) for many of the variables evaluated. The
variation in soil loss between soils was much greater than the variables in runoff . There was a sig2
nificant ( P < 0105) interaction between year and soil for many of the variables evaluated. Alberts
et al. inferred from the limited experimental results that the climate factor and time2variant soil
properties such as bulk density , soil st rength , aggregate size and stability might to be important
in influencing runoff and erosion response like antecedent moisture. Bajracharya and Lal [7 ] as2
sessed the seasonal soil loss and erodibility (factor K of the USL E) variation on a Miamian silt
loam soil using three replicate runoff plots (22 by 4m) . The results showed that soil loss and
erodibility varied significantly among seasons. Erodibility was high under wet , thawing soil con2
ditions during the winter and spring due to low soil st rength and greater susceptibility to detach2
ment . Summer erodibilities were lowest in each year despite high soil loss f rom erosive rains. The
same experimental results were also obtained by Wilcox[5 ] . According to the studies on runoff and
erosion mechanisms for 2 years. Wilcox proposed the following hypotheses : soil erodibility follows
an annual cycle ; it is greatest at the end of the freeze2thaw period in late winter and lowest in the
end of the summer rainy season , when soils have been compacted by repeated rainfall. Rill erodi2
bility was found to be highly variable (0173～16131 ×103 s/ m) on fresh tilled treatment , but
variability decreased significantly for 89 days or more since tillage , stabilizing in the range of 2～
5 ×103 s/ m[6 ] . Characteristics of soil erosion during periods of snowing and thawing were de2
scribed by Nagasawa et al. [31 ] . Soil loss was 13 times greater f rom frozen than from unfrozen
bare2soil lysimeters due to changes in soil erodibility as a result of f reezing. Soil erosion rates f rom
the frozen grassland lysimeters was 1/ 16 of the rate f rom the frozen bare soil lysimeters. A similar
relationship was observed between the equivalent unfrozen plots. Nagasawa pointed out that the
031 核　农　学　报 13 卷
increase in surface erodibility resulted from the action of f reezing and thawing.
Up to now , however , little research has been made to assess the temporal variations in erodi2
bility and time2variant soil condition factors affecting erodibility at different field scales because of
the great inherent soil heterogeneity. Resampling close to previously dug pit is not a guarantee of
similarity , since up to half of the variance within a plot can be present within any square meter of
it [32 ] .
The relationships between soil erodibility parameter and topography have , until recently ,
been difficult to ascertain due to the difficulty of quantifying soil erosion rates necessary to derive
erodibility parameters at specific locations in the landscape. Thus , only very few studies on the
spatial variability in erodibility parameters have been made[11 ,12 ,33～27 ] .
Martz[33 ] assessed the variation of soil erodibility with slope position in a cultivated Canadian
prairie landscape by simulated rainfall. In Martz’s experiment , the soil loss produced by simulat2
ed rainfall on undisturbed soils was used as an index of relative soil erodibility. Relative erodibility
and several soil properties , were measured at the summit , shoulder , midslope , footslope and toes2
lope of 11 slope transects in an area of cultivated grassland soils on hummocky glacial till . The re2
sults indicated that erodibility was 14 % greater on the shoulder and midslope , and 21 % less on
the toeslope , than those on the summit and footslope. Local variation in erodibility along slopes
was considered to be an important control on patterns of soil erosion in the landscape. The varia2
tion of erodibility along the slopes reflected soil property trends. The greatest erodibility was asso2
ciated with upper slope positions where soils tended to be shallow , coarse , poorly leached and low
in organic matter , while lower erodibility was found at lower slope positions with deep , organic2
rich and leached soils.
Frielinghaus and Schmidt [11 ] concluded that the dist ribution of soil types within different
grades of catenas plays an important role in determining the extent of erosion in the Pleistocene
moraine lanclscape of N. Germany. The upper part of the slope is the outflow position , with loss
of nutrients and OM and presence of eroded soils. The lower part is the inflow position , with ad2
ditions of nutrients and OM and development of colluvial soils. The middle , t ransit position may
show normal soils , but on steep slopes this zone is very narrow. The site factors which increase
the risk of water erosion above that of adjacent areas include type of catena , thickness of the Ah
horizon , soil OM content , vegetation , infilt ration and structural stability. The variations in soil
erodibility parameters with slope positions have also been shown by Kinnell [12 ,35 ] . The regional
variability in erodibility factor ( K of USL E) at macro2level has been described by Neemann[36 ] ,
Jager and Rickson[37 ] .
These studies are undoubtly a breakthrough for predicting soil erodibility. In general , how2
ever , there was no obvious functional relation between climate zone or geographic position and soil
erodibility parameters and no theory from which to predict one. Furthermore , soil erodibility , a
critical parameter in erosion prediction , is the most difficult parameter to measure. Thus , a fur2
ther quantitative assessment of spatial variability in soil erodibility parameters is st rongly needed.
The first task in studying the variations in erodibility within a wide region is to search after the
131　3 期 利用137Cs 技术研究土壤可蚀性的时空变异
techniques which can be used for determining soil erodibility and understanding the major factors
controlling its spatial variability at different landscape levels.
Determining
The existing methods of determining erodibility parameters can be grouped into two cate2
gories : erosion modeling and prediction methods , and erosion measurement methods[38 ] . In all
cases , there is a need for direct derivation from soil erosion measurement data , which can be done
using simulated rainfall and natural rainfall in erosion plots[6 ,19 ,39 ] by hydraulic flume meth2
ods[40～42 ] , surveying methods[43 ,44 ] and tracer techniques[45 ] .
Field erosion plots should be a representative part of the landscape under study. This method
is costly and labor intensive. Use of small plots reveals serious limitation in providing information
on the local variability in erosion and within field deposition [45 ] . In view of the variability in soil
erodibility parameters in a particular climate , accurate estimates of the erodibility would require
the collection of data for at least 10 years. In addition , for the results to be comparable and repre2
sentative , well designed experiments using standardized methodologies for measuring soil erosion
should be performed[38 ] .
Surveying methods provide valuable qualitative information on a large area , but it has impor2
tant limitation for quantitatively assessing temporal and spatial variations in erodibility parame2
ters.
Another group of techniques is based on natural labeling by fallout radionuclides such as the
bomb2derived fallout 137Cs during the 1950s and early 1960s. This approach overcomes many of
the problems associated with the traditional approaches. Particular advantages of fallout 137 Cs
technique includes the possibility of obtaining retrospective estimates of long2term (ca 40 years)
rates of soil loss within the landscape on the basis of a single visit and of assembling data with both
spatial patterns and rates of total erosion/ deposition involved. The validity and value of the fallout
137Cs approach have now been demonstrated by numerous studies in a number of environments. In
essence , use of 137Cs technique involves either evaluating the shape of the 137Cs profiles in the sed2
iment or , alternatively , comparing the measured inventories (total activity in the soil profile per
unit area) at study sites with an estimate of the total atmospheric input obtained from a“reference
site”[33 ,47～58 ] .
Perspective for the 137Cs approach
To date , most of the studies employing 137Cs technique have been concerned with soil erosion
by water and tillage , but there is clearly potential for extending its application to wind ero2
sion[58～60 ] .
Although to date there is little work on the assessment of erodibility by 137 Cs techniques ,
some evidence suggests that 137 Cs content in eroded soils by wind and water may be related to
231 核　农　学　报 13 卷
some soil erodibility indices[45 ,58 ] . Data obtained by Elliott et al [45 ] showed that the aggregate sta2
bility index of Collis2George and Figueroa explained the most variations caesium2137 content
(52 %) . Variations in organic matter content explained 27 per cent of the variations in caesium
levels. The values of the correlation coefficients of the relationships between the other erodibility
indices such as aggregation and clay dispersion examined and caesium2137 levels were low. Ritchie
and McHenry[61 ] found that the factors best correlated with soil caesium2137 content were three
plant growth factors , soil organic matter , nit rogen and phosphorus. A multiple linear regression
established by Harper and Gilkes[58 ] indicated that organic carbon content and the mean grain size
of the eroded soil by wind explained 35 % of the variation in 137Cs content . Similar positive rela2
tionships between 137 Cs activity and organic carbon content were also reported[62 ] , with up to
50 % of 137Cs in deposits being associated with organic matter[63 ] . These results suggest that there
are many factors included in erodibility assessment by 137 Cs techniques. But the most important
might be the changes in soil st ructure , soil moisture , infilt ration and the cycling of organic mat2
ter , which are st rongly influenced by plant root systems[41 ,42 ,63 ] and landscape posi2
tions[11 ,32 ,64～66 ] .
Most work to date has focused on applying 137Cs measurements within small areas , common2
ly individual fields for one crop or for one slope. But scope exists for using caesium measurement
to provide a number of individual point estimates of erosion rates within a larger area[48 ,49 ,53 ] .
137Cs techniques affords one of the few viable means of assessing the impact of tillage on soil
redist ribution[54～66 ] and the spatial dist ribution data generated are ideally suited to coupling with
GIS and spatial statistics[49 ,57 ,55 ] . This potential may offer very important information about spa2
tial variability in soil erodibility and its estimation for a larger and , therefore more representative
area. These possibilities merit further investigation.
In many areas of Europe the Chernobyl accident (2620421986) caused additional inputs of
137Cs fallout . These additional inputs f requently complicate the interpretation of 137 Cs measure2
ments , but they can also offer a unique opportunity to investigate the erosion history[67 ,68 ] and
therefore variations in erodibility parameters of an area. Further work is required to explore this
possibility.
Acknowledgement :This work is part of the project supported by Alexander von Humboldt Foun2
dation ⅣCHN 1039279.
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利用137Cs 技术研究土壤可蚀性的时空变异
李 　勇
(中国科学院山地灾害与环境研究所　成都　610041 ,中国农业科学院原子能利用研究所　北京　100094)
Frielinghaus M 　Bork H R
(德国农业景观与土地利用研究中心)
土壤可蚀性的研究变异性是当代土壤侵蚀预测预报研究的核心。本文综述了土壤可蚀性变
异性研究的进展及存在的问题 ,提出了利用137Cs法定量测定土壤可蚀性时空变异的新技术。
关键词 :土壤可蚀性 　土壤侵蚀 　时空变异 　137Cs
631 Acta A gricult urae N ucleatae Sinica
1999 , 　13 (3) :129～136