Agriculture Reference
In-Depth Information
growth and consequently to boost crop productivity. Since deficiency of P (the
second most important plant nutrient after N) is an important chemical factor
restricting plant growth, chemical phosphatic fertilizers are widely used to achieve
optimum yields (Del Campillo et al.
1999
; Shenoy and Kalagudi
2005
). Soluble
forms of P fertilizer after application are, however, easily and rapidly precipitated
as insoluble forms and become inaccessible to plants (Goldstein
1986
; Takahashi
and Anwar
2007
). The deficiency of P in turn can severely limit plant growth and
productivity (Fern´ndez et al.
2007
), particularly in legumes, where both the plants
and their symbiotic bacteria are affected. As a result, this may have a deleterious
effect on nodule formation, development, and function (Robson et al.
1981
). Unde-
niably, synthetic fertilizers have resulted in better crop yields but at the cost of
deteriorating fertility of soils leading ultimately to human health problems via food
chain. There is therefore urgent need to find alternative option to eliminate or at
least minimize too much dependence on chemical fertilizers so that the use of
biofertilizers on a large scale in agronomic practices could be popularized among
farm practitioners. The application of beneficial soil microbes especially
phosphate-solubilizing organisms (Krishnaveni
2010
; Yu et al.
2011
; Zhu
et al.
2011
; Bashan et al.
2013
; Dugar et al.
2013
; Sharma et al.
2013
) used both
alone and in combination with other compatible microbes (Zaidi et al.
2003
; Zaidi
and Khan
2006
; Wani et al
2007a
; Awasthi et al.
2011
; Khan et al.
2013
) has
provided some solutions to the ever-increasing use of expensive synthetic fertilizers
in farming system. Such microorganisms when used in agriculture practices provide
benefits to plants in different ways, for example, they assist in maintaining long-
term soil fertility by providing good soil biological activity, suppressing pathogenic
soil organisms, and stimulating microbial activity in the rhizosphere (Biswas and
Narayanasamy
2006
; Ouahmane et al.
2007
; Collavino et al.
2010
; Parani and Saha
2012
). Accordingly, it is reported that the phosphate-solubilizing (PS) bacteria
when applied with other plant growth-promoting rhizobacteria (PGPR) could
reduce P fertilizer application by 50 % without any significant reduction in crop
yields (Jilani et al.
2007
; Yazdani et al.
2009
) suggesting that PS organisms as
inoculant/biofertilizers hold greater promise for sustaining crop production (Wani
et al.
2007b
; Deepa et al.
2010
). Here, we highlight the impact of PS microbes on
the growth and yield of certain widely grown legumes and cereal crops in different
production systems.
8.2 Synthetic Fertilizers and Soil Microorganisms: Benefits
and Deleterious Impact
Synthetic fertilizers are widely used in agricultural practices particularly in devel-
oping countries to enhance soil fertility and, hence, crop production. Some argue
that fertilizer was as important as seed in the Green Revolution (Tomich et al.
1995
)
period contributing as much as 50 % of the yield growth in Asia (FAO
1998
;
