VOLUM OMAGIAL - Facultatea de Ştiinţe ale Naturii şi Ştiinţe Agricole

Elena Delca / Ovidius University Annals, Biology-Ecology Series 14: 181-184 (2010)
After six months of application of organic and
inorganic amendments microbial abundance showed
considerable changes in some cases, so the highest
density was recorded in the experimental group
fertilized with manure, variant III, in which case we
determined a density of 501.79 x 10 6 CFU/g dry soil
(Fig. 2). The number of bacteria also increased
significantly in variant VI up to 142.13 x 10 6 CFU/g
dry soil (Fig. 2).
Paradoxically, after six months I have noticed
decrease of heterotrophic bacteria in variant I, which
might be explained by the effect of administration of
chemical fertilizers and organic substance
consumption by bacteria. In autumn 2009 the initial
amount of organic matter in the form of crop residue
remaining after harvest decreased gradually as the
decomposition and microbial consumption
progressed and provide sufficient nutrients to
maintain viable bacterial population as numerous as
in the beginning of the experiment. In other variants
(II, IV and V) microbial density presented weakly
peaks compared with the control, and ranged between
30.73 x 10 6 CFU/g soil dry and 46.31 x 10 6 CFU/g
soil dry (Fig. 2), situation observed also in control
variant.
At the beginning of the experiment, density of
free nitrogen-fixing bacteria was relatively low, (Fig.
3), ranging from 10.3 x 10 5 CFU/g dry soil to 26.7 x
10 5 CFU/g dry soil. In case of variants I, III, V and
VI values are very close to those recorded for control
(Fig. 3).
Fig. 3 Changes of abundance of nitrogen-fixing
bacteria (October 2009)
183
The highest number recorded for variants II and
IV ranging between 22.7 x 10 5 CFU/g dry soil and
26.7 x 10 5 CFU/g dry soil, rely on local trophic
conditions.
In any case, there was a certain uniformity of
abundance of nitrogen-fixing bacteria beginning of
the experiment. At this stage relatively low
abundance of nitrogen-fixing bacteria could be due to
higher quantity of organic substance that stimulates
competition within heterotrophic bacterial
populations.
Fig. 4 Change in binding density micro N2, after six
months (May 2010)
After six months of adding the fertilizers our
estimations revealed a significant increase of the
number of nitrogen-fixing bacteria, including that of
the control (Fig. 4).
Most evident increase of abundance of this
group occurred I in variant III, where we recorded
about 195.81 x 10 5 CFU/g dry soil (Fig. 4).
Significant increases were recorded in the case
of variants II, IV and VI, where abundance ranged
from 90.44 x 10 5 CFU/g dry soil to 127.39 x 10 5
CFU/g dry soil (Fig. 4).
In variant I and V, values were close to the
abundance determined for control (Fig. 4).
Table 1. Agrochemical analysis conducted in autumn
2009
Nr.
Crt.
Variant % mg/Kg
Humus Indice N2
1 V1 2.9 0.14