|
1. Definition
| Name |
ROCK
FRAGMENTS |
| Brief
definition |
Unattached pieces of rocks
of 2 mm diameter or larger that are strongly cemented or more
resistant to rupture. They are present on the soil surface
or distributed in various quantities into the soil body.
 |
Soil
formed on conglomerate parent material containing high
amounts of rock fragments (photo by C. Kosmas) |
|
| Unit
of measure |
percentage
of rock fragment cover on soil surface or of soil volume. |
2. Position
within the logical framework DPSIR
3. Target and
political pertinence
| Objective |
Contribution
to the definition and mapping of ESAs. |
| Importance
with respect to desertification |
Rock fragments,
especially on the soil surface can have a great but variable
effect on soil water conservation and soil erosion. Cobbles
generally restrict evaporative water loss during periods of
no- to moderate drought (e.g. from late fall to early summer)
but they increase evaporation during the dry and hot summer.
The higher amounts of soil moisture in stony soils, especially
in late spring to early summer, positively affect plant growth
and productivity of rainfed crops supporting a considerable
biomass production, and protecting large areas from desertification.
Pebbles on the soil surface can reduce surface water runoff
and soil loss playing an important role on land protection in
the Mediterranean region from desertification. |
| International
Conventions and agreements |
The CCD emphasizes
that combating desertification must be tackled within the general
framework of actions to promote sustainable development. |
| Secondary
objectives of the indicator |
Soils
containing considerable amount of rock fragments become warmer
earlier in spring than the same soils free of rock fragments.
This favours early plant growth and better use of available
water. Rock fragments on the soil surface can be used as an
indicator for defining desertification risk of sloping cultivated
land. |
4. Methodological
description and basic definitions
| Definitions
and basic concepts |
Rock fragments are classified
according to their diameter to the following categories: pebbles
(diameter 2-75 mm), cobbles (diameter 75-250 mm), stones (diameter
250-600 mm), boulders (diameter >600 mm). The presence
of various sizes of rock fragments on the soil surface can
have a multifunctional effect on protecting hilly areas from
desertification. Cobbles, despite the increasing run-off and
erosion have a beneficial effect on soil moisture conservation
under conditions of moderate water stress. Pebbles, despite
the non-significant contribution to soil water conservation,
reduce surface water runoff and sediment loss under heavy
and prolonged rainfall events. Even though the presence of
rock fragments on the soil can adversely affects tillage operations
and the quality of certain agricultural products such as potatoes,
carrots and beets. They should not removed from the soil,
especially from hilly areas.
 |
Changes
in wheat biomass production measured along catenas in
adjacent plots with and without rock fragments in the
soil surface in hilly areas of Greece (source: C. Kosmas)
|
|
| Benchmarks
Indication of the values/ranges of value |
- rock fragment cover
> 40%,
- rock fragment cover
15-40%,
- rock fragment cover<15%
|
| Methods of
measurement |
Rock fragment
content on the soil surface can be easily estimated in the field
as percentage of the surface covered. Such data are also available
in regular soil survey reports. |
| Limits of the
indicator |
The beneficial
effect of rock fragments in protecting hilly areas from desertification
under Mediterranean conditions is highly limited if percentage
cover is less than 15% on the soil surface. |
| Linkages
with other indicators |
Parent
material, Slope gradient,
Drainage, Soil
depth, Infiltration
capacity, Soil texture |
5. Evaluation
of data needs and availability
| Data required
to calculate the indicator |
Percentage
of soil surface covered by rock fragments for each soil mapping
unit. Independent of rock fragment size. |
| Data sources |
Necessary data
are usually available on regular soil survey reports and the
cost/benefit ratio is reasonable. |
| Availability
of data from national and international sources |
Data can be
obtained from various regional, national or international institutions
involved in the collection and elaboration of soil survey data. |
6. Institutions
that have participated in developing the indicator
| Main institutions
responsible |
Agricultural
University of Athens, Katholieke Universiteit de Leuven
|
| Other contributing
organizations |
Universities
of Lisbon, Murcia, Basilicata, Amsterdam, Leeds
|
7. Additional
information
| Bibliography
|
Kosmas, C.,
Kirkby, M. and Geeson, N. 1999. Manual on: Key indicators of
desertification and mapping environmentally sensitive areas
to desertification. European Commission, Energy, Environment
and Sustainable Development, EUR 18882, 87 p. |
| Other references |
Danalatos, N.G., Kosmas,
C.S., Driessen P.M. and Yassoglou, N. 1994. Estimation of
the draining soil moisture characteristics from standard data
as recorded in routine soil surveys. Geoderma 64:155-165.
Moustakas, N.C., C.S.
Kosmas, N.G. Danalatos and N. Yassoglou, 1995. Rock fragments
I: Their effect on runoff, erosion and soil properties under
field conditions. Soil Use and Management, 11: 115-120.
Poesen, J., 1990. Conditions
for the evacuation of rock fragments from cultivated upland
areas during rainstorms. In: Proceedings of the Jerusalem
Workshop on erosion, transport and deposition processes, IAHS
Publication, 189:145-160.
Wesemael, B. van, Poesen,
J., Kosmas, C., Danalatos N., and Nachatergaele, 1996. Evaporation
from cultivated soils containing rock fragments, Hydrology
J. 182:65-82.
|
| Contacts Name
and address |
Agricultural University
of Athens, Laboratory of Soils and Agricultural Chemistry,
Iera Odos 75, Athens 11855, Greece
Dr Constantinos Kosmas
email: lsos2kok@aua.gr
|
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