Agriculture Reference
In-Depth Information
The humus content is very high, ranging between 4 and 11%. In all cases, the humification
processes favors the formation of fulvic acids, a most unusual process in soils with high base
saturation. This process is illustrated by the relatively high values of fulvic acid carbon (CF = 300
to 600 mg/100 g soil) and especially by the ratio between humic and fulvic acid carbon, which is
mainly below (0.5 to 0.9) or slightly above (1.1 to 1.4) unity. The presence of ionic aluminum (2
to 80 ppm) and of ionizable SiO
2
(50 to 300 ppm) in the soil solution of the saturated soil ensures
suitable conditions for the formation of aluminum-fulvate and aluminum-silicate gels. As our
experiments indicate, these are very efficient binding materials for soil aggregates. Differences in
the base content and in aluminum and iron ion content, as well as in texture, account for the
differences in stability of soil aggregates in the three investigated soils.
In summary, the morphology, micromorphology, and physical and chemical properties of these
soils allow the identification of new vermic subtypes in mountain rendzinas, brown eubasic earths,
and podzolic brown soils that result from the high pedogenetic activity of the soil fauna, dominated
by giant earthworms of the genus
Octodrilus
.
E
XPERIMENTAL
S
TUDY
OF
THE
I
NFLUENCE
OF
C
ALCOPHILOUS
O
CTODRILUS
S
PECIES
ON
S
OIL
As discussed in this chapter, several of the endemic
Octodrilus
species may be regarded as
calcophilous, their occurrence confined to rendzinas and eubasic brown earths distributed in patches
underlying beech or beech-hornbeam forests. These relatively small areas of soils developed on
limestone are isolated from one another by soils developed on acid rocks. It was suggested (V.V.
Pop 1994) that these acid soils could be regarded as barriers to the spreading of calcophilous
earthworms, thereby promoting an accelerated insularlike speciation of the genus
Octodrilus
.
Some of these
Octodrilus
species, such as
O. frivaldszkyi
,
O. aporus, O. permagnus
, or
O.
ophiomorphus
, are very large earthworms and are believed to play an important role in developing
the most evident vermic features recorded so far in the soils of the northern temperate zone.
In a laboratory experiment, the relationships between
Octodrilus
species and calcium in the
development of vermic structures in soil was investigated. Calcium is an important factor in
stabilizing soil structure, and its concentration is also considered a key factor in determining the
distribution of certain earthworms. The degree of stenobiotism toward calcium was also investigated
by testing the tolerance of calcophilous earthworms to acid soils, presumed to act as barriers to
their distribution (Pop et al. 1992).
Material and Methods
The activity of two calcophilous earthworm species,
O. frivaldszkyi
and
O. bihariensis,
in three
different soils, either with or without supplementary calcium carbonate, was investigated in sub-
terranean laboratory conditions.
Octodrilus frivaldszkyi
is a very large earthworm (length 400 to
500 mm, diameter 8 to 15 mm, weight 20 to 25 g), and
O. bihariensis
is a medium-size earthworm
(length 94 to 113 mm, diameter 4 to 7 mm, weight 2 to 3 g). The soil types used in the experiment
were (1) a vermic cambic rendzina from beech forest (1100 m altitude), Padis karstic area; (2) an
acid brown soil from fir tree forest (1400-m altitude), Baisoara, the Apuseni Mountains; and (3)
an albic luvisol from a mixed beech-oak forest (700-m altitude) near Cluj-Napoca. The rendzina
represents the natural habitat of the two earthworm species studied; the acid soils, which separate
the limestone areas in the Apuseni Mountains, can be considered a hostile environment.
Experimental cages were filled with soil material (passed through 2-mm mesh sieve) from the
A horizon of the three soils. For each soil type, cultures with and without a supplementary calcium
carbonate layer were designed. The earthworms were fed with dried beech leaves. Experiments
were in a subterranean laboratory in a deep cellar with air humidity close to saturation and a
temperature of 8 to 12AC for 16 months (November 1987 to March 1988).
