Agriculture Reference
In-Depth Information
4.1
Introduction
Phosphorus is one of the major plant nutrients and plays some important physio-
logical and biochemical roles in plant growth and development (Bagyaraj
et al.
2000
). However, a greater part of soil P, approximately 95-99 %, is insoluble
and, hence, cannot be utilized by the plants. The rapid fixation of P by soil
constituents leads to soil P deficiency. This necessitates the application of P
fertilizer to the P-deficient soils regularly in agricultural practices in order to fulfil
the phosphatic demands of crops. However, most of the available P added to
calcareous soils may become unavailable within a short period of time (Tisdal
et al.
1995
). Considering the brisk P-fixing ability of calcareous soils and increasing
cost of P fertilizers, scientists suggested adding P to the soils as raw material
(e.g. rock P) after pulverizing it (Antonio and David
1997
). In the last decades,
several strategies were applied to reduce the P fixation through the following:
(i) use of high rates of P fertilizers, (ii) selection of fertilizers, (iii) time and method
of application, (iv) combination with amendments and other fertilizers, (v) use of
soil tests, etc. (Engelstad and Terman
1980
). However, the efficiency of P fertilizers
is still low and range between 5 and 10 % (Havlin et al.
1999
). In modern agronomic
practices, enormous amounts of synthetic P fertilizers are applied, which however,
adversely affects the environment (Brady and Weil
1999
). Therefore, primary
approach in agronomic management of P is to scavenge the native/fixed P and
also to overcome the fixation of applied P fertilizer. In this respect, the use of
microorganisms capable of mobilizing P into available/soluble forms as
biofertilizers is feasible, particularly in sustainable agriculture production systems.
Hence, there is enormous interest in isolating PSM, including P-solubilizing and
P-mineralizing saprophytic fungi (phospho-fungi), due to their large biomass-
producing ability, high metabolic activity and ability to maintain solubilizing
capacity for longer periods. Such phospho-fungi have been isolated from various
soils (Pandey et al.
2008
; Morales et al.
2011
). The rationale for using such
P-solubilizing fungi as an alternative to synthetic phosphatic fertilizer in agriculture
is highlighted.
4.2 Rationale for Mineral P Solubilizers
For sustained agricultural production, use of efficient fertilizer to maintain the soil
and plant quality is critical. The application of synthetic fertilizers has been
practised for more than a thousand years in many countries since it provides
essential nutrients to plants, improves soil structure, helps in the moisture-retaining
capacity of various soils and increases microbial activities (Chen et al.
2006
). In
developing countries like India, the stress on agriculture is increasing day by day.
The land under farming is declining and this has posed an extra pressure on
agriculture. There are reports that most of the agricultural lands are deprived of
