Agriculture Reference
In-Depth Information
in order to coat them with the biofertilizer. The results obtained confirmed the
suitability of these formulations to increase crop growth, nutrient content of various
plant components, and other yield attributing parameters. Other carriers have also
been tested. For example, Negi et al. (
2005
) prepared PSB inoculants by mixing
bacterial suspensions of four strains of CT
Pseudomonas fluorescens
with a mixture
of talc powder and carboxy-methyl cellulose. Talc is considered an excellent
coating agent, preventing caking (often occurring during both storage and trans-
portation of biofertilizers), improving fertilizer flow, and reducing water pickup and
dust. The formulation developed by Negi et al. was air-dried, packed in autoclaved
polybags, and stored at
20
C. When pea seeds were treated by this formulation,
its effectiveness in promoting plant growth and inhibiting phytopathogens was
confirmed. Alternatively, formulations based on natural, hydrophilic polymers
like sodium alginate have also been proposed and tested for their potential as CT
bacterial carriers (Trivedi et al.
2005
; Trivedi and Pandey
2007
,
2008a
,
b
). Sodium
alginate, for instance, a highly porous polymer when appropriately prepared, was
used by Bashan in
1986
to develop a new inoculant carrier, capable of slowly
releasing the entrapped PGPB in the rhizosphere of crops. Since then, it has been
widely used as a suitable carrier for biofertilizer development, even though it is
more expensive than charcoal. In
2005
, Trivedi et al. tested five carrier-based
preparations of plant growth-promoting bacterial inoculants suitable for use in
cool regions, namely, (1) alginate beads, (2) alginate beads supplemented with
skim milk, (3) alginate-coated seeds, (4) charcoal-based, and (5) broth-based
preparations. Two well-known PGPR were included in the formulations:
Bacillus
subtilis
(NRRLB-30408) and
Pseudomonas corrugata
(NRRL B-30409) using
maize (var. QPM-1) as test crop in plant growth promotion assays conducted at
22
C. Even though all the formulations tested increased the measured parameters
of maize relative to untreated control, alginate-based formulations were the most
effective, followed by charcoal- and broth-based formulations, respectively. Long-
term rhizosphere colonization was also shown to be more efficient when applying
alginate-based formulations as compared to charcoal- and broth-based formula-
tions. Similar growth promotion effects were obtained for wheat when an alginate-
based formulation of
P. putida
(MTCC6842) was applied to the soil at the time of
sowing in a pot assay conducted at temperatures ranging between 10 and 15
C
(Trivedi and Pandey
2007
). The success of alginate-based formulations was further
confirmed using
B. megaterium
B388—as PGPB—and maize or wheat as test
species (Trivedi and Pandey
2008a
). Again, a maximum increase in the growth
parameters of both plant species was observed in the case of alginate-based
formulations followed by coal- and broth-based formulations, respectively. On
the other hand, viability of bacterial inoculants after 180 days of storage at 4
C
was confirmed in formulations containing alginate beads and alginate beads
supplemented with skim milk (Trivedi et al.
2005
). Trivedi and Pandey (
2008b
)
further reported the survival, viability, and plant growth-promoting ability of
B. subtilis
(NRRLB-30408) and P.
corrugata
(NRRL B-30409) immobilized in
sodium alginate beads after 3 years of storage at 4
C. When using coal or broth for
the same purpose, the decrease in bacterial viability for the same period was much
