『Abstract
The soil's resistance to concentrated flow erosion is an important
factor for predicting rill and (ephemeral) gully erosion rates.
While it is often treated as a calibration parameter in process-based
soil erosion models, global change studies require the estimation
of erosion resistance from measurable soil properties. Several
laboratory and field experiments have been conducted to determine
the erosion resistance of various types of soils, but no attempts
have been made hitherto to summarize all these data and to explore
them for general trends. In this study, all available data on
the resistance of topsoils to concentrated flow erosion in terms
of channel erodibility (Kc) and critical
shear stress (τcr) has been collected together
with all soil and environmental properties reported in literature
to affect the soil erosion resistance. Reported Kc
values for cropland topsoils range between 0.002 10-3
s m-1 and 250 10-3 s m-1(n=470),
whereas τcr values range between 0 and 15
Pa (n=522). It is demonstrated that so far, the heterogeneity
of measurement methods, the lack of standardized definitions and
the shortcomings of the flow shear stress model hamper the comparability
of soil erosion resistance values from different datasets. Nevertheless,
combining Kc and τcr
data from different datasets, a general soil erosion resistance
ranking for different soil textures can be proposed. The compiled
dataset also reveals that tillage practices clearly affect Kc (Kc for conventional tillage＞Kc for reduced tillage＞Kc
for no tillage) but not τcr.
It was concluded that Kc and τcr
are not related to each other and that soil and macro-environmental
properties affecting the foremost do not necessarily affect the
latter as well and vise versa. Often Kc seems
to be a more appropriate parameter than τcr
to represent the differences in soil erosion resistance under
various soil and environmental conditions (e.g. bulk density,
moisture content, consolidation, tillage). The two parameters
represent different quantities and are therefore both needed to
characterize the soil's resistance to concentrated flow erosion.
Keywords: soil erosion resistance; critical shear stress; soil
erodibility; concentrated flow; flume experiments; soil properties;
tillage practices』
1. Introduction
2. Soil resistance to concentrated flow erosion in current process-based
models
2.1. Predicting soil detachment from simple hydraulic indicators
2.1.1. Excess shear stress models
2.1.2. Excess stream power models
2.2. Predicting soil detachment using a transport capacity deficit
approach
2.3. Predicting soil detachment using probability density functions
2.4. Comparison of the different approaches
3. Data collection
4. Results
4.1. Data range of the experimental Kc
and τcr values
4.2. Relationship between Kc and τcr
4.3. Trends in erosion resistance emerging from the compiled
dataset
4.3.1. The effect of soil texture
4.3.2. The effect of tillage practices
5. Discussion
5.1. Causes for the large range in Kc
and τcr values
5.1.1. Different experimental procedures
5.1.1.1. Field plot experiments
5.1.1.2. Laboratory flume experiments
5.1.1.3. Other experimental procedures
5.1.1.4. Comparison of the experimental approaches
5.1.2. Different definitions for soil erosion resistance
5.2. Overview of soil and environmental characteristics affecting
Kc and τcr
5.2.1. Soil properties
5.2.1.1. Texture
5.2.1.2. Rock fragment content
5.2.1.3. Soil moisture conditions
5.2.1.4. Mechanical and structural soil properties
5.2.1.4.1. Compaction
5.2.1.4.2. Shear strength
5.2.1.4.3. Structural stability of soil aggregates and plasticity
5.2.1.5. Organic matter content
5.2.2. Land use and agricultural practices
5.2.2.1. Crop type
5.2.2.2. Tillage
5.2.2.3. Incorporated crop residue
5.2.3. Chemical and biological properties
5.2.3.1. Chemical properties
5.2.3.2. Biological properties
5.2.3.2.1. Plant shoots
5.2.3.2.2. Living and dead plant roots
5.2.4. Micro-climatic properties
5.2.4.1. Soil temperature
5.2.4.2. Frost action
5.2.5. Pore water properties
5.2.6. Different response of Kc and τcr
5.3. An appraisal of the excess shear stress equation
5.3.1. Do drag forces control detachment?
5.3.2. Is average flow shear stress a good soil detachment predictor?
5.3.3. Does form shear stress contribute to soil detachment?
5.3.4. Does Dr increase linearly with τ?
5.3.5. What is the effect of the applied range of τ?
5.3.6. What is the significance of τcr?
5.4. Predicting soil erosion resistance
5.4.1. Measurement and calibration of Kc
and τcr
5.4.2. Prediction of Kc and τcr
in process-based models
6. Conclusions
Acknowledgments
References