|
1. Definition
| Name |
SOIL
PERMEABILITY |
| Brief definition |
In hydrology,
permeability describes the capacity of soil to transmit water.
It depends upon the pores in the soil and how they are connected.
It is a dynamic soil property that is affected by soil organisms,
land use and soil moisture. |
| Unit of measure |
m/day, cm/hour
or mm/hour |
| Spatial scale |
local |
| Temporal
scale |
minutes
to weeks |
2. Position
within the logical framework DPSIR
| Type of Indicator |
state, impact
and response |
3. Target and
political pertinence
| Objective |
Changes
in permeability can be easily monitored and used to demonstrate
positive or negative impacts of land use. These include soil
structure decline, compaction or improvement resulting from
soil management. It is used as a headline indicator in the United
States Rangeland Assessment Methodology. It can be used as part
of a soil quality score card. |
| Importance
with respect to desertification |
Permeability
is primarily an indicator of the ability of the soil to store
water. The general values reflect the rocks and vegetation that
make up the specific geo-ecosystem (e.g. basalt, limestone,
marls and granite). It is usually high beneath plants where
there are many macropores, but low in areas of clayey soils.
It is greatly affected by loss of organic matter, soil compaction
(cultivation and grazing). Changes in permeability can provide
an early warning of soil degradation, flood risk and erosion.
The level of permeability is also indicative of the potential
water and nutrient availability to plants. Loss of permeability
is probably a major cause of flooding. Hydrological models require
estimations of permeability to predict runoff. When soils become
dispersive, because of the accumulation of salts by evaporation,
this can cause an order of magnitude drop in the permeability. |
| International
Conventions and agreements |
Although attention
is given to soil depth and erosion as key indicators, a good
case could be made for soil permeability as it gives early warning.
It is not just soil depth that is important but the capacity
of the soil to store water and to retain its integrity under
the forces of erosion. |
| Secondary objectives
of the indicator |
As a general
measure of soil quality and management performance. |
4. Methodological
description and basic definitions
| Definitions
and basic concepts |
In
arid, semi-arid and dry sub-humid areas, soil permeability is
spatially and temporarily highly variable. Distinctions are
made between the types of macro-meso-micro permeability that
occur on cultivated and natural systems. With macro-permeability,
there may be a ploughpan with a low permeability at a depth
of about 30 - 40 cm. At the micro scale, permeability reflects
the activities of soil organisms. Irrigation can have a negative
impact on permeability if soils are not managed properly. |
| Benchmarks
Indication of the values/ranges of value |
Values of permeability
are highly variable in semi-natural systems (e.g. 0.5 to 15
cm/hour). During rainfall values decline as soils respond to
wetting. The saturated hydraulic conductivity of a soil (one
measure of the permeability) should in general be in the order
of several mm/hour but preferably several cm per hour. Macro
pores mean that very highly permeable conditions frequently
exist adjacent to zones of low permeability. |
| Methods of
measurement |
In situ measurements
and estimations can be made using improvised ring infiltrometers
constructed from cans, or by augering a hole and measuring the
rate at which water poured into it declines during a specified
period of time. With a ring, the water should be kept at a constant
head about 3 cm above the surface and the amount of water added
to the ring recorded. Field testing kits are described in the
literature. Rain water or demineralised water should be used
for the test. For larger areas rainfall simulation experiments
can be used. Digging a hole and making a sketch of the variation
in the wetting front can be used to record variations in permeability
after natural and simulated rainfall. |
| Limits
of the indicator |
Often,
reported values are unreliable because poor quality water is
used in the test. The actual values measured are sensitive to
details of the experiment. What is interesting is the general
order of magnitude and the changes that occur in time, and the
patterns that are observed in the field. |
| Linkages
with other indicators |
Erosion
risk (RDI), Infiltration
capacity, Parent material,
Soil crusting, Soil
erosion (USLE), Soil quality
index, Soil texture, Water
storage capacity, Management
quality index, Tillage
operations, Grazing intensity,
Runoff water storage,
Water availability. |
5. Evaluation
of data needs and availability
| Data
required to calculate the indicator |
This
field measurement determinations needed to calculate this indicator
has not been systematically collected in Europe. In the USA
this is now the case. They could be collected by farmers as
a compliance (response) indicator. |
| Data
sources |
Organisations
responsible for soil and water conservation, land owners and
land users. |
| Availability
of data from national and international sources |
Some data available
from Agricultural and Environmental Services. Examples of how
to organise and collect data can be found in the USA. |
6. Institutions
that have participated in developing the indicator
| Main
institutions responsible |
Foundation
for Sustainable Development (3D-EC), Netherlands |
| Other contributing
organizations |
Many organisations
such as the ESSC, CSIC, the Universities of Ghent, Wageningen,
Amsterdam and INRA and Valencia and the agricultural University
of Athens have contributed to the development of this indicator
|
7. Additional
information
| Bibliography
|
** missing |
| Other references |
|
| Contacts Name
and address |
A.C. Imeson
Foundation for Sustainable Development (3D-EC), Netherlands
3de@hetnet.nl
|
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