Agriculture Reference
In-Depth Information
humate and fulvic acid, for example, has been found to improve P solubilization by
B. megaterium
var.
phosphaticum
from insoluble TCP, and the amounts of P
solubilized were in proportion to the quantities of the humic substances added
(Khan et al.
2009
). Humic and fulvic acids react with the insoluble TCP and release
soluble P. Of these, fulvic acid releases more P than sodium humate. Humic
substances on the other hands act as strong complex forming and chelating agents.
The chelation property of humic substances is thus of great use in increasing the
efficiency of P fertilizers which are rendered insoluble through fixation mecha-
nisms. In a study, a pot experiment was conducted at green house (LRRI) NARC,
Islamabad, on loamy soil during kharif season of year 2012, to investigate the
interactive effect of HA, PSB, and varying level of P on P use efficiency in
chickpeas. The N, P, and K contents were found to be significantly increased by
the application of HA (50 mg HA/kg) and PSB inoculation, and maximum N
(4.5 %), P (36 %), and K (2.15 %) contents were recorded in chickpea grown in
the presence of 50 mg P
2
O
5
/kg. Also, the nutrient availability in soil was also
improved following single or mixed application of HA, PSB, and P (Sarwar
et al.
2013
). From this study it has been suggested that the combined application
of HA, P, and PSB inoculation improves nutrient use efficiency and could help in
reducing the use of P fertilizer by 25 % for chickpea production (Sarwar
et al.
2013
). In a similar study the combined effects of humic compounds and
PSB (
Pseudomonas putida
) were investigated to increase the yields of soybean,
grown under glasshouse experiment. The humic compounds were extracted from
rice straw compost, the PSB were obtained from Bogor Agricultural University, and
the soils (Typic Paleudult) for this experiment were collected from Kentrong
Banten, Indonesia. The results showed that the application of humic compounds
together with PSB inoculation increased the pH and available P, while it decreased
the exchangeable Al of an ultisol (Winarso et al.
2011
). The improved soil charac-
teristic, however, did not lead to any significant difference in the uptake of
macronutrients by soybean plant (Winarso et al.
2011
). The application of organic
matter has been found to improve the physical, chemical, and biological properties
of soil, which in turn provide a better environment for the growth and activity of the
indigenous/introduced PSM.
3.2.8 Kinds of Substrate
Phosphate-solubilizing microorganisms have been found to solubilize a variety of P
compounds including DCP and TCP, Fe and Al-P, bone meal, apatites, and differ-
ent types of RP. In a study, the production of soluble P by
Burkholderia cepacia
DA23 with TCP and hydroxylapatite was higher compared to Al-P, and the
production also increased following increase in amounts of the insoluble P (Song
et al.
2008
). The reactivity of PRs, the main constituent of which is mineral apatite
(Ca
5
(PO
4
)
3
X) where X is predominantly fluorine, is determined by the rate of
dissolution in acid and the amount of P recovery. The reactivity also depends on
