Agriculture Reference
In-Depth Information
Different studies report a better assimilation of nutrients when the chemical fertilization
is complemented with beneficial microorganisms. For example, Sundara et al.
(2002) found
that the application of the PSB
Bacillus megatherium
var.
phosphaticum
increase the
availability of P in the soil, improving growth, yield and quality of sugarcane. When used in
conjunction with phosphate fertilizers this PSB reduce the required dose of P by 25%.
Moreover, it was shown that when applied in combination with phosphate rock,
B.
megatherium
can help saving up to 50% of the production costs by replacing superphosphate.
The effects of a combined treatment consisting of a multifunctional biofertilizer (mixture of
Bacillus sp., B. subtilis, B. erythropolis, B. pumilus
and
P. rubiacearum
) plus 50% of the
recommended chemical fertilization dose was compared with the complete chemical
fertilization dose on the growth of lettuce and water celery. The results of this study indicated
a 25% increase of lettuce yield and 34% dry matter increase of water celery in the biological-
chemical treatment (Young et al.
,
2003; 2004) as compared to the chemical fertilization
treatment alone, indicating that at least 50% of the chemical fertilization can be saved by a
complementary approach of multifunctional biofertilizers and chemical fertilizers.
Benítez-Noyola (2013) demonstrated that maize plants fertilized with 90 and 180 Kg N
ha
-1
and inoculated with
Paenibacillus polymyxa
extracted from 20 to 28% more nitrogen and
produced more grain than plants that were only chemically fertilized. These effects were
explained in terms of increased root growth and nutrient availability.
Obando et al. (2013) found a statistically significant increase of 4% in the nitrogen
removal by maize plants chemically fertilized (urea) and biofertilized with
Azotobacter
chroococcum
AC1, with respect to plants that were only chemically fertilized.
Compared to individual application of nitrogen fertilization, Das et al.
(2004) found
greater N
2
nitrogen accumulation in cotton when chemical fertilization was combined with
Azotobacter
M4. The increased nitrate assimilation promoted by
Azotobacter sp
. may be
related to a greater elongation of root hairs, which would improve the ability to absorb
nutrients and water (Obando et al.
,
2013).
Dibut et al.
(2009) mention that by using
Azotobacter chroococcum
they were able to
reduce 30% the recommended dose of nitrogen fertilization (urea) for banana without
affecting crop yield because of the atmospheric nitrogen fixing capacity of
A. chroococcum,
which they demonstrated by isotopic techniques (
15
N). These authors also indicate that
inoculation of chickpea plants with
Mesorhizobium cicerii
resulted in beneficial effects on
different parameters of growth and development, which permitted a reduction of 70% of the
recommended nitrogen (urea) dose without affecting grain yield (2.05 ton ha
-1
) as compared
to control plants fertilized with 100 kg N ha
-1
that produced 1.98 ton ha
-1
.
According to Biswas et al. (2000) nitrogen-fixing microorganisms can promote plant
growth by transferring the fixed nitrogen to plants or by enhancing the absorption of nutrients
through the modulation of the hormonal activity. In this sense, Bashan (1999) mentions that
inoculation of plant growth promoting microorganisms, such as
Azospirillum sp.,
results in
increased accumulation of nitrogenous compounds by promoting a more effective absorption
of nutrients with no apparent nitrogen fixation. Conversely, Shamsuddin (1994), using the
15
N
isotope technique, found that up to 89% of the N requirement of oil palm plantlets is supplied
by the symbiosis with
Azospirillum.
(Mia et al., 2010)
Covarrubias-Ramírez
et al. (2005) evaluated the kinetics and efficiency of P uptake in
potato plants (
Solanum tuberosum
L.) cv. Alpha, through
32
P isotope technique. They
demonstrated that the inoculation of
Bacillus subtilis
increased the potato biomass by 31.7%
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