Agriculture Reference
In-Depth Information
the groups
Aranae, Chilopoda, Diploploda, Diplura, Pauropoda, Protura
and
Symphila
were collected. In addition to these, individuals of the insect
orders
Dermaptera, Hemiptera, Homoptera, Isoptera
and
Thysanoptera
were found in limited numbers.
The higher biological diversity in the organic system is important be-
cause it contributes to keeping the biological equilibrium, essential in an
agroecosystem. This equilibrium may bring about greater stability for the
system and consequently fewer problems with diseases and pests.
With respect to the worm community, after a one-year period of crop-
ping, the soil in the organic system showed at least a ten-fold higher num-
ber of specimens per 3140 mL soil sample than the conventional system.
After 370, 407 and 471 days from planting a total of 18, 24 and 101 speci-
mens were found in the organic cropping system, and 1, 2 and 12 spec-
imens were found in the conventional system, respectively. These data
agree with Bokhorst (1989), who found that the number of worm indi-
viduals per square meter, in a soil planted with sugar beets, was fi ve times
higher in the organic system as compared to the conventional. Also, El Titi
& Ipach (1989) observed the existence of greater worm biomass in a low-
input system than in the conventional. The higher number of species in
the organic system is possibly due to the availability of organic substrates
for them to breed on and the absence of pesticides. On the other hand, the
presence of pesticides explains the small number of species in the con-
ventional system, since the worms are sensitive to the products used in
the conventional system (Lee, 1985). These organisms are important be-
cause they not only improve the physical properties (Lee, 1985), but also
contribute to the soil's ability to suppress pathogens, such as
R. solani,
among others (Stephens et al., 1993). No worm specimens were found in
the recently plowed soil (81 days before planting) and in the evaluations
carried out at planting time and 90 days after planting the seeding, as well
as in the organic compost.
