Agriculture Reference
In-Depth Information
the composition of the apatite mineral, presence of impurities, and particle size.
Increasing the degree of substitution of carbonate for P and of magnesium and
sodium for Ca in the apatite structure and decreasing particle size enhance the
reactivity of PRs (Chien and Menon
1995
). The solubilization of apatites and RP
depends upon the chemical composition and arrangements of minerals, which
increase their resistance to solubilization as compared to DCP and TCP. The
maximum RP solubilization has been reported with particle size ranging between
30 and 99 mesh. The efficiency of solubilization, however, gets reduced when the
size of RP is finer compared to coarser particles. The solubilization of RP of varying
particle sizes, due to inoculation with efficient solubilizing
A. awamori
and
P. striata,
is reported to be maximum when RP size is between 30 to 59 and
60 to 99 (Gaur
1986
). Microbial conversion is less obvious with finer RP particles
than with coarser particles. However, complete solubilization of RP never occurs
because a part of RP is so strongly bound that even concentrated HCI or H
2
SO
4
cannot solubilize it (Gaur
1986
). Other P sources are Udaipur rock phosphate
(UPR), Mussoorie rock phosphate (MRP), and North Carolina rock phosphate
(NCRP) which have fluorapatite structure with the highest substitution of P with
carbonate in NCRP (Narayanasamy and Biswas
1998
). The higher solubilization
and lowered quantities of organic acids detected in the presence of NCRP could be
due to the higher reactivity and greater diversion of organic acids in the neutral-
ization of free carbonates in the solubilization of NCRP as compared to MRP and
URP (Bolland
2007
). Likewise, the higher solubilization and production of organic
acids in the presence of TCP could be attributed to its amorphous nature with simple
structure and absence of any free carbonates as compared to the crystalline lattice
structure of the RP (Kumari et al.
2008
). The decreasing soil pH also increases PR
effectiveness (Rivaie et al.
2008
; Chien et al.
2010
) and dissolution, which has been
shown to be linearly correlated with the reserve acidity of the soil.
3.2.9 Effect of Salt Concentrations
Soils containing salts have various ions that may obstruct the uptake of water and
concurrently be toxic to numerous soil microflora (Zahran
1997
; Rietz and Haynes
2003
; Tripathi et al.
2006
; Yuan et al.
2007
; Vanessa et al.
2008
; Li et al.
2011
).
However, phosphobacteria among microbes have been found in even highly saline
environments, for example, marine habitat (Chookietwattana and Maneewan
2012
;
Promod and Dhevendaran
1987
). Phosphate-solubilizing microorganisms when
grown in salt-affected environments exhibit variable responses (Table
3.2
)to
different concentrations (Srinivasan et al.
2012
) and compositions of salts (Yadav
et al.
2011
). For example,
Pseudomonas aeruginosa
,
P. putida
,
P. cepacia,
and
P. fluorescens
when grown in the presence of varying concentrations of salts (NaCl)
displayed optimum P solubilization at 0-1.25 % NaCl, but the higher concen-
trations of NaCl delayed the P solubilization process (Deshwal and Kumar
2013
).
In a similar study, the effect of salt concentrations (0 %, 2 %, 4 %, 6 %, and 8 %) on
