PhD Thesis
Soil
type and the previous
tensile strength and penetration resistance
as a
(PR)
should
allow the
soil
compared ranging
fail
to
failure planes in between the microaggregates.
function of
easily along
Five Tanzanian soil
hardsetting Paleustalf
from a
extreme of strength behaviour, through a Paleudoll,
Paleustult,
both
It was expected
(the strength characteristics).
that microaggregation
types were
can
I characterized soil strength by measuring
affect soil strength.
matric potential
cultivation
history of
one
at
Paleudalf and a
to a strongly microaggregated Orthox expected to be at
At each site soils that had a history of
the weak end of the scale.
7 or more years of cultivation and cropping were compared with newly
cultivated
soils.
The
and
Orthox
Paleustult
had
the
best
PR
characteristic for ease of root growth and the Paleustalf had the
worst characteristic which suggested that it would not permit root
growth at matric suctions exceeding 100 kPa.
The Orthox also had
much the most favourable tensile strength characteristic.
At air
dryness (100 MPa suction), the previously uncultivated and previously
cultivated
Orthox
topsoils
strength.
compressive)
Paleustalf topsoils.
Paleustult)
a
previous
had
3
and
respectively,
9
times
than
less
the
tensile
(and
corresponding
For three of the soils (Orthox, Paleudoll and
history
of
cultivation was
found
to
have
significantly and substantially reduced the tensile strength of the
topsoil at any given matric suction compared to the newly cultivated soil