Agriculture Reference
In-Depth Information
Similar results were obtained by Castro et al. (1993), when several types
of soybean management were compared, and by Cattelan & Vidor (1990)
on soils cultivated with different crop rotation systems. Grigorova &
Norris (1990) justified not adopting this method for evaluating soil mi-
croorganisms, because only a small fraction of microbial biomass could
be cultivated on a selective medium. However, Cattelan & Vidor (1990)
demonstrated the effectiveness of the method in studies with different
cropping systems. In spite of a similar behavior in regard to microbial
populations, starting 145 days after planting the tomatoes, the bacteria
populations (Figure 1 C) were higher in the organic system as compared
to the conventional. This could be due to soil plant cover, like Cattelan &
Vidor (1990) who found a smaller bacterial population on naked as com-
pared to cultivated soil.
Soil total respiratory activity continued higher in the organic system
during the crop cycles, showing in some evaluations twice as much as
the evolution observed in the conventional system (Figure 2). Differences
were found during the intermediate period, that is, between 142 and 400
days after planting. There were no statistical differences between treat-
ments at the initial periods or at the end. The higher respiratory rate in the
organic system could be due to the addition of an exogenous source of
organic matter to the soil and the consequent stimulation of heterotrophic
microorganisms (Lambais, 1997).
Observed organic matter decomposition rates ranged from 15 to 45%
of organic carbon loss in a 20-day period. Rodrigues et al. (1997) observed,
in corn cultivated during the summer, values reaching 70% of carbon loss
in a period of 30 days. There was no difference among results from the or-
ganic and the conventional systems (Figure 3). However, regardless of the
system, there was an infl uence of time on the organic matter decomposi-
tion rate was, although no interaction between time and the treatments was
found. This suggests that variations found during the study period could be
related to the humidity and temperature fl uctuations that occur in the fi eld,
thus providing no evidence that the adopted management forms infl uenced
decomposition rate.
The CO
2
release method used in this study to evaluate respiratory ac-
tivity favors the microorganism population, since soil manipulation can
eliminate the majority of the microarthropod community. Several authors
