Agriculture Reference
In-Depth Information
Table 9.2
Effect of application of organic acids on P solubilization (mg kg
1
) in soil
P solubilization in PSB
non-inoculated treatments
P solubilization in PSB
inoculated treatments
Dose of organic acids applied (mM)
Oxalic acid
Malic acid
Oxalic acid Malic acid
0
18.80
18.80
22.55
22.55
10
21.50
19.12
27.23
22.77
20
24.57
20.35
28.37
21.57
30
23.55
19.70
26.15
19.55
Source: modified from Panhwar et al. (
2013
)
PSB
phosphate-solubilizing bacteria
Significant and constant quantities of organic acids might be detected in the soil
solution (Shen et al.
1996
). However, the amount of organic acids was found to be
very low in the soil solution, usually from 1 to 50
M (Strobel
2001
). In other
investigation, low amounts of residual organic acids were found in the soil.
However, organic acid concentration in soil is not stable and it can vary with the
passage of time (Table
9.3
). Similar findings of Jones (
1998
) and Strobel (
2001
)
showed that the organic acid concentration in soil solution would be different at
different space and time.
μ
9.3.2.4 Ammonium Assimilation
Plant supply of nitrogen might have a computable consequence on pH change
because of the H
+
release from plant roots through ammonium assimilation
(NH
4
+
). In the plants that rely on NH
4
+
rather than NO
3
to reduce pH, the cation
uptake ratio will be increased as compared to the anions (Gahoonia et al.
1992
).
Microbial excretion of H
+
is also similar to plants under the assimilation of cations,
mainly associated to N source. It is well understood that microbes H
+
are exerted in
exchange for NH
4
+
(Asea et al.
1988
), and it is reported that high P is solubilized
due to the NH
+
4
rather than NO
3
nitrogen (Whitelaw et al.
1999
). Furthermore,
among N sources, ammonium sulfate is known to support high P solubilization for
different bacterial species,
Bacillus circulans
,
B. brevis
, and
B. coagulans
(Vora
and Shelat
1998
).
9.3.2.5 Organic Phosphate Solubilization
In most soils, the organic forms of P are 30-50 %, while in other soils they may be
as low as 5 % and as high as 95 % (Paul and Clark
1989
). Organic P in the soil is
mostly present in the form of inositol phosphate (soil phytate). An organic form is
the most stable form in the soil and accounts for up to 50 % of the total organic P. It
is synthesized mostly in soil by microorganisms and by plants (Harley and Smith
1983
). Phosphomonoesters, phosphodiesters including phospholipids and nucleic
acids, and phosphotriesters are the other organic P compounds in soil. Organic P
