Agriculture Reference
In-Depth Information
In the six subsequent months (Table 2), when only the families of mites
were quantifi ed, the largest population was of Scheloribatidae followed by
Galumnidae, with similar behavior between the systems. The expressive
number of individuals in the families
Galumnidae
and
Scheloribatidae
for
both cropping systems is due to the characteristic these families exhibit
toward occupying space in agroecosystems. In the orders
Actinedida
and
Gamasida
, families
Cunaxidae
and
Laelapidae
were the largest, respec-
tively. In general, mite population densities in the classes
Gamasida
and
Actinedida
were higher in the organic system. The fact that the
Gamasida
showed high numbers is possibly due to a large
Collembola
population,
because these organisms are a source of food for this class of mites. El Titi
& Ipach (1989) verifi ed the existence of larger populations of collembo-
lans and Gamasida mites in the low-input system than in the conventional.
Due to the more abundance of microarthropods in the organic system,
it was believed that the organic matter decomposition rate would be higher
in this system, because these organisms contribute for organic matter deg-
radation and stimulate microbial activity in the soil (Nosek, 1981). Ac-
cordingly, when the presence of
Oribatida
and
Collembola
in litterbags
incorporated into the organic and the conventional systems was evaluated,
a larger number of individuals in the litterbags was found for the organic
system (Melo & Ligo, 1999), indicating that this system contributes for
an increase in biological diversity. Since the presence of these organ-
isms in larger numbers was not accompanied by a higher decomposition
of organic matter, one can say that the differences in arthropod density
found in the soil between the organic and the conventional systems did
not refl ect on the organic matter decomposition rate, as evaluated by the
litterbag method. The community of microarthropods in the soil might
have, among other factors, infl uenced microbial activity, since the organic
system showed a higher microbial activity potential than the conventional
system. The infl uence of the soil fauna on the organic matter decomposi-
tion rate of forest soils is well documented, but this is not true for agricul-
tural ecosystems (Crossley et al., 1989). In agroecosystems the effect of
the fauna on the organic matter decomposition rate seems not to be very
signifi cant and consequently, there are many points that need to be clari-
fi ed when it comes to the role of fauna in agricultural soils. Occasionally,
and similarly among the crop systems evaluated, individuals belonging in
