Agriculture Reference
In-Depth Information
This activity was significantly influenced by C and N sources. In pot-based assays,
conducted under greenhouse conditions at 25
C, all the three species enhanced
maize and wheat production. Similarly
Paecilomyces hepiali
, a psychrotolerant
fungal species isolated from rock soil of a cold desert site in Indian Himalaya, was
also shown to slowly and steadily solubilize P at low (suboptimal) temperatures
(i.e., 14
C) (Rinu and Pandey
2011
). This ability was attributed to the production of
organic acids and the consequent acidification of the culture medium.
5.7 Cold-Tolerant Bioinoculants
Application of PSB in agronomic practices started about 60 years ago, when a large
proportion of the former Soviet Union's agricultural soils were inoculated with a
biofertilizer consisting of kaolin-impregnated
Bacillus megaterium
var.
phosphaticum
spores to increase their fertility (Mishustin and Naumova
1962
).
The results were so spectacular that, in some cases, up to 70 % increases in crop
yields were recorded and this was mainly related to P mobilization. The success of
Phosphobacterin, as this bioinoculant was called, reflected not only the importance
in selecting an appropriate PGPB strain but also the paramount role of a good
carrier (kaolin) for the biofertilizer preparation. Indeed, from both a commercial
and agricultural point of view, the success of a biofertilizer strongly depends on the
development of appropriate formulations, easy to be handled and stored for long
periods of time. As highlighted by Bashan (
1998
), a good carrier for PGPB should
have the capacity to deliver the right number of viable cells, in appropriate
physiological condition and at the right time. It should also protect bacterial cells
from the various biotic and abiotic stresses they will face once applied to the soil.
Furthermore, bacteria carried this way must retain their PGP abilities after long
periods of storage. Lastly, when considering developing countries, an ideal carrier
should be of low cost and locally available. Alas, even though many formulations
have been tested, no universal formulation for CT-PSB inoculants is presently
available.
Again, efforts have been extensive in this field and mostly made by Indian
researchers, aimed at using locally available, low-cost organic raw materials as
carriers. Charcoal, for instance, has been employed in many formulations because it
is inexpensive and easily available in plenty everywhere. However, the low quality
of charcoal may sometimes affect badly its water holding capacity, bulk density,
and porosity (NIIR Board
2012
). Only the use of good quality charcoal is therefore
recommended for bioinoculant formulations. A series of greenhouse and field
experiments have been conducted in the last 10 years using charcoal-based
CT-PSB inoculants (more appropriately CT-PGPB) (Kumar et al.
2007
; Trivedi
et al.
2007
; Mishra et al.
2009b
; Rinu and Pandey
2009
; Vyas et al.
2010
). In
general, the bacterial cultures were grown first in appropriate culture media, mixed
with sterilized activated charcoal (usually in combination with a gluing and stabi-
lizing agent like raw sugar or carboxy-methyl cellulose) and, then, applied to seeds
