Chemistry Reference
In-Depth Information
introduction of beneficial organisms to the soil.
18
Soil macrofauna, especially
earthworms and termites, are important components of the soil ecosystem and
as ecosystem engineers they influence formation and maintenance of the soil
structure and regulate soil processes. Earthworms and termites have different
feeding strategies which, in turn, affect their impact on soil. Because of their
sensitivity to disturbance and their importance in redistributing and
transforming organic inputs, earthworms and termites represent an important
indicator of soil quality.
Soil invertebrates are important determinants of biological, chemical and
physical characteristics. They enhance biodegradation and humification of
organic residues in several ways: (1) by breaking down organic residues and
increasing surface area for microbial activity; (2) by producing enzymes which
break down complex bio-molecules into simple compounds to form humus;
and (3) by improving the soil environment for microbial growth and soil-plant
interactions.
19-21
The diversity and abundance of the structures produced by soil ecosystem
engineers, e.g. earthworms and termites, impact on the physical properties of
soils, i.e. overall aggregation, porosity, water infiltration and retention and
resistance to erosion.
22
Earthworms play an important role in the formation of
soil organic matter (SOM) enriched macroaggregates,
23-26
which can
physically protect occluded organic matter against microbial decay and, upon
disintegration, release occluded carbon and nutrients.
23,27
Apart from
promoting soil physical and chemical properties, earthworms also promote
nodulation,
28
dispersal of mycorrhizal fungi,
29
and even disease suppression
and dispersal.
30
Termites mediate the synthesis and breakdown of soil organic
matter and influence water infiltration and availability to plants by modifying
soil structure.
31-35
They influence soil physical properties through the
construction of mounds, nests, galleries and surface sheeting
31,34,36
and also
by transporting materials, thereby producing passages which improve drainage
and aeration.
37-39
Mound-building termites form stable microaggregates that
physically protect occluded organic matter against rapid decomposition and
reduce soil erosion and crust formation.
40,41
The importance of termites in the decomposition of plant matter in natural
ecosystems is well documented;
42-45
it has been established that in the tropical
rainforests of Nigeria termites play a significant role in both decomposition
and litter removal. Mando and Brussard
42
found that termites alone could
account for up to 80% of litter disappearance in one year. Termites play a
significant role in soil nutrient availability and cycling through interactions
with other soil organisms, e.g. bacteria and fungi, to most of which they
provide food.
40
Soil from termite mounds is sometimes used as fertiliser in
tropical cropping systems because of a high accumulation of nutrients.
46,47
Despite the potentially beneficial role of termites, termite pest problems have
been identified as a major constraint to increasing yields of crops in sub-
Saharan Africa.
48,49
d
n
1
r
2
n
g
|
4
The challenge therefore remains to better understand the
