|
1. Definition
| Name |
TILLAGE
DEPTH |
| Brief
definition |
Tillage depth corresponds
to depth that a tillage implement such as mouldboard plough,
cultivator, chisel plough, harrow etc. is disturbing the soil.
The deeper the soil is ploughed the greater the soil displacement
in the direction of tillage.
 |
A
mouldboard used for deep plough of soil (photo by C. Kosmas)
|
|
| Unit
of measure |
centimetres,
meters |
2. Position
within the logical framework DPSIR
| Type of Indicator |
Driving force |
3. Target and
political pertinence
| Objective |
Contribution
to the evaluation of the desertification risk of an area. |
| Importance
with respect to desertification |
Soils in hilly
areas formed on consolidated parent materials such as limestone,
shale, sandstone, igneous rocks have a restricted depth. Deep
soil ploughing especially in the downslope direction, a displacement
of the ploughing layer occurs in the same direction. Such a
displacement results in a translocation of the soil from the
upper landscape positions and to the lower landscape positions.
The reduction in soil depth results in diminishing effective
soil depth for the growing plants. Several studies have been
shown that tillage erosion can contribute up to 70% of the soil
loss in hilly cultivated areas. It is estimated that about 8%
of the agricultural land is abandoned or has to be abandoned
due to high erosion rates occurring during the last decades
after the introduction of the tractor in agriculture. |
| 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 |
Within
the ESA mode for investigation of the individual processes linked
to land degradation and desertification.
|
4. Methodological
description and basic definitions
| Definitions
and basic concepts |
The rate of soil loss
due to tillage erosion is affected by various factors such
as tillage direction, tillage depth, type of tillage implement,
tractor wheel speed, soil moisture content, slope gradient
etc. The introduction of heavy powerful tractors in cultivating
the land in the last decades resulted in increasing the ploughing
depth from 15-20 cm to 30-40 cm. Such change in plough depth
resulted in high erosion rates due to tillage. Recently farmers
realised that deep ploughing was unnecessary creating major
problems in crop production and started decreasing plough
depth. Detailed studies on hilly sloping areas (slope 22%)
have been shown a displacement of the surface layer for about
1 meter when the soil was ploughed downslope at the depth
of 40 cm. A 50% reduction in plough depth can reduce soil
displacement by more than 75%.
Studies have shown that
mean soil displacement under the same slope gradient decreases
significantly as plough depth decreases. Furthermore, slope
gradient also affects soil displacement. A 50% reduction of
slope gradient can decrease soil displacement for about 60%
for the same plough depth.
The effect of plough depth
on soil displacement is especially pronounced on steep slopes
where the furrow slice with shallow ploughing sometimes is
not completely turn but remains in an angle usually perpendicular
to the soil surface, so that soil displacement is greatly
reduced. Steeper convex hillslope parts greatly favour reversion
and breaking down of furrow slice. When furrow slice is reversed
in the down or up slope direction (independently of tractor
travel direction), soil displacement is greater because gravity
acts as an additional force displacing farther the soil. Of
course other parameters besides slope gradient and ploughing
depth could affect reversion and breaking down of furrow as
tractor speed, soil moisture content, soil consistence, rock
fragment content, etc. Mouldboard plough with the soil displaced
in the up slope direction (tractor travel up slope) may be
considered as a cultivation practice reducing land degradation
of hilly areas due to tillage erosion. In all cases of up
slope plough, there is a net up slope soil displacement. That
again varies with plough depth and slope gradient. Generally,
up slope soil displacement is significantly lower than down
slope displacement.
Measurements of soil displacement
conducted in hilly areas in Greece (see figure) shows that
mean soil displacement is related to slope gradient. The slope
of the linear regression curve increases as plough depth increases,
reflecting the importance of decreasing plough depth for reducing
tillage erosion especially in hilly areas with steep slopes.
 |
Relation
of mean soil displacement and slope gradient for three
plough depths and tillage direction perpendicular to the
contour lines (Gerontidis et al., 2001) |
Several authors have used
a diffusion type equation in calculating the net soil flux
due to tillage. The soil diffusion constant (k, in kg m-1
) can be estimated from the equation k = - PD*BD*B, where
PD is the plough depth in meters, BD is the bulk density of
soil in kg m-3, B is a coefficient obtained by the linear
regression analysis of mean displacement distance (MD) and
slope gradient (S) by the equation MD = A+B*S (see figure).
Field measurements in Greece have shown that diffusion constant
can range from 153 kg m-1 (±25.6 kg m-1 ) to 670 kg
m-1 (±113.6 kg m-1 ) as plough depth increases from
20 cm to 40 cm. Farmers used to plough the soil deeper and
deeper in recent years. The average plough depth has changed
from 25 cm to 40 cm in Greece in the last two decades. The
great increase of soil diffusion constant as plough depth
increases points to the increasing importance of tillage erosion
in degrading hilly areas.
|
| Benchmarks
Indication of the values/ranges of value |
plough depth:
|
| Methods of
measurement |
By conducting
the land user or the extension services of the related institutes.
Also plough depth can be easily measured in the field by digging
the upper soil layer and measuring the depth in which tillage
implements reach. |
| Limits of the
indicator |
Tillage erosion
is especially important for hilly cultivated areas. It is not
important in plain areas where soil displacement is limited.
|
| Linkages
with other indicators |
Tillage
direction, Slope gradient,
Soil
depth
|
5. Evaluation
of data needs and availability
| Data required
to calculate the indicator |
Plough depth
|
| Data sources |
Necessary data
are usually available and accessible for a region depending
on the land use type. |
| Availability
of data from national and international sources |
Data
can be easily obtained from various regional, national or international
institutions and land users. |
6. Institutions
that have participated in developing the indicator
| Main institutions
responsible |
Agricultural
University of Athens
|
| Other
contributing organizations |
Universities
of Lisbon, Murcia, Basilicata, Amsterdam, Leeds
|
7. Additional
information
| Bibliography
|
TERON project
- Tillage erosion: current state, future trends and prevention.
Contract:. FAIR3-CT96-1478 |
| Other references |
Gerontidis St., Kosmas,
C., Detsis, V., Marathainou, M., Zafiriou, Th., and Tsara,
M. 2001. The effect of mouldboard plough on tillage erosion
along a hillslope. Soil and Water Conservation J. 56:147-152.
Govers G Vandaele K Desmet
PJJ Poesen J & Bunte K 1994. The role of tillage in soil
redistribution on hillslopes. European Journal of Soil Science
45, 469-478.
Lindstrom, M.J.., Nelson,
W.W., and Schumacher T.E., 1992. Quantifying tillage erosion
rates due to moldboard plowing. Soil & Tillage Research.
24:243-255.
Tsara, M., Gerontidis,
S., Marathianou, M., & C. Kosmas, 2001. The long-term
effect of tillage on soil displacement of hilly areas used
for growing wheat in Greece. Soil Use and Management, Vol.
17, pp. 113 - 120.
|
| Contacts
Name and address |
Agricultural
University of Athens
Dr Constantinos Kosmas
email: lsos2kok@aua.gr |
|
