SOIL ORGANISMS IN ORGANIC AND CONVENTIONAL CROPPING SYSTEMS - Organic Agricultural Practices - page 42

this system (Paschoal, 1995). Not only does the system have to satisfy the
need for reducing the environmental negative-impact problems caused by
intensive agriculture, it must also be economically competitive. In com-
paring the organic and the conventional cropping systems, an important
step is to establish which social, economic and ecological factors influ-
ence the production systems the most. Besides, a knowledge of those fac-
tors allows for a better understanding of how the production systems are
structured and how they work.
With respect to the biological activity, in studies to compare the con-
ventional, integrated and organic cropping systems, Bokhorst (1989)
found that the number of worms in a soil planted with sugar beets was
fi ve times higher in the organic system than in other systems, and that the
percentage of wheat and potato roots infected with arbuscular mycorrhizae
was twice as high in the organic as compared to the conventional and inte-
grated systems. Gliessman et al. (1990, 1996), working with similar objec-
tives, compared conventional and organic strawberry cropping systems in
areas where farmers became organic producers, and verifi ed an increase
in the number of plants infected with mycorrhizae. Swezey et al. (1994)
found higher microbial biomass in the soil and in arbuscular mycorrhizae
in the organic system than in the conventional, in an area being changed
from conventional into an organic apple growing area. All these studies
emphasize the biological elasticity in the organic systems as a fundamen-
tal characteristic, infl uencing the occurrence of pests and diseases.
With regard to soil organisms, Brussaard et al. (1988, 1990) verifi ed
that the total biomass of soil organisms was higher for the integrated than
for the conventional cropping system, with fi gures averaging 907 kg C ha -1
and 690 kg C ha -1 , respectively. Of these biomasses, bacteria accounted
for over 90%, fungi represented approximately 5% and protozoa were less
than 2% of the total biomass. El Titi & Ipach (1989) studied the effect of
a cropping system with low input rate index as well as the conventional
system on the soil fauna components and observed there were smaller
populations of nematodes pathogenic to plants, higher worm biomass, and
larger populations of collembolans and Mesostigmata mites in the system
with low input index. Collembola is a microarthropod related to the soil's
capacity to suppress Rhizoctonia solani (Lartey et al., 1994). Rickerl et al.
(1989) found that populations of this organism were 29% larger in soils