Agriculture Reference
In-Depth Information
solubilization, and declined thereafter. The amount of Pi released among PSF in
general declined with enhancing NaCl concentration at all incubation periods
(Srinivasan et al.
2012
). According to Kumar et al. (
2010
) P solubilization also
increased with an increase in NaCl concentration. Realizing the variable impact of
salts on microbial structure and function, the impact of salts on P-solubilizing
organisms and barley crops inoculated with PSB was conducted (El-Din and
Saber
1983
). A significant increase in P uptake by plants due to inoculation was
observed, but this increase was negatively correlated with increasing salinity levels.
The strong promotion of growth of plants, percent Pi release by PSM, and P uptake
by plants due to combined interactions of plants and microbes provide evidence that
crop productivity could be improved in P-deficient soils affected by salinity. The
tomato (
Lycopersicon esculentum
) seeds inoculated with halotolerant PSB strains
and grown in different saline conditions exhibited a significant increase in germi-
nation percentage of the seeds at salt concentration between 0 and 60 mM,
suggesting that the isolated halotolerant PSB may provide P to the growing plants
under saline conditions (Soni et al.
2013
).
3.2.10 Factors Affecting Organic P Mineralization
The availability of organic P depends on microbial activity to break down the
organic matter (OM) and release this P into available forms. The organic P
availability depends on physico-chemical characteristics of soils such as (i) soil
conditions and weathering process, which influence microbial activity; (ii) soil pH,
temperature, and warm moist conditions; and (iii) nutrient levels of soils. Of these
factors, temperature above 30
C has the maximum positive impact on minerali-
zation of organic P, while the optimum temperature supporting P solubilization is
35
C. Below 30
C net immobilization of P occurs. The moisture range of 50-75 %
of total WHC is considered optimum for mineralization of organic P although it
may also occur in flooded conditions. Alternate wetting and drying favour mineral-
ization of P as it breaks up water stable soil aggregates and exposes for decompo-
sition of otherwise inaccessible humic matter to microorganisms. Other factors that
affect organic P mineralization are the cultivation practices (Hedley et al.
1982
;
Miguel and Wright
2008
) which stimulate microbial activity following aeration and
facilitate faster decomposition of OM. Hence, cultivated soils generally contain less
organic P than virgin soils. Also, cultivation decreases phytate, phospholipids, and
nucleic acid P compounds but increases non-hydrolysable residues. Although the
effect of aeration is not always consistent, but due to poor aeration, the organic
matter decomposition decreases particularly at O
2
levels below 1 % of partial
pressure of O
2
in atmosphere. The mineralization of organic P is mediated through
certain enzymes which indeed are influenced by several factors. For example, the
availability of phosphatases, one of the several enzymes involved in the mineral-
ization of organic P in soil, is enhanced by organic residue addition because P ties
up as insoluble Fe, Al, and Ca. Addition of inorganic P may also increase the
