Agriculture Reference
In-Depth Information
Hopper
1993
). Others have found that one-third of the cereal production worldwide
is due to the use of fertilizer and related factors of production (Bumb
1995
).
Fertilizer consumption in many countries including India has increased substan-
tially in recent times, and today India is probably the largest producer and consumer
of fertilizers in the world. According to some estimates, the total fertilizer con-
sumption in India was 26.49 million nutrient tonnes in 2009-2010 (Jaga and
Yogesh
2012
). The importance/use of fertilizers for crop yield is likely to increase
further in order to achieve optimum agriculture production and consequently to
feed the alarmingly increasing human populations. This is due to two reasons:
(1) cultivable land is declining rapidly and there is little scope for bringing more
area under cultivation and (2) majority of soils over the world including Indian soils
are deficient in many essential nutrients including P. However, the accumulation of
such fertilizers in soils which results from the excessive and repeated application
and poor uptake by plants significantly affects biological and biochemical proper-
ties of soils (Marschner
2003
; Yevdokimov et al.
2008
; Zhong et al.
2010
). More-
over, studies have mainly been conducted at a bulk soil scale or in short-term
experiments, and as a result, there is still little information available on rhizosphere
effects on extracellular enzyme activities and microbial community structure in
agricultural soils, influenced by long-term practices. Among various factors,
organic matter (OM) addition has been found to cause a rapid shift in the activities
of various enzymes and reactivation of biogeochemical cycles in bulk soil
(Madejon et al.
2001
; Bastida et al.
2007
). It is generally recognized that OM
addition tends to increase the total microbial biomass, though the responses of
specific groups such as Gram-positive bacteria, Gram-negative bacteria, and fungi
vary greatly. For instance, OM additions often result in increased or altered fungal
populations (Bastida et al.
2007
), variable populations of arbuscular mycorrhizal
(AM) fungi (Corkidi et al.
2002
), shifts in Gram-positive and Gram-negative
bacteria (Peacock et al.
2001
; Marschner
2003
), and increased fungi/bacteria ratios
(Elfstrand et al.
2007
). Importantly, the response of the microbial community
structure to OM additions tends to be based on differences in the carbon amount
or quality of the organic amendments. Inorganic fertilizers such as N, P, and K have
also been reported to have a contrasting impact on structure and activities of soil
microbes (Goyal et al.
1999
;B¨hme et al.
2005
) especially the P-solubilizers. As an
example, Bolle et al. (
2013
) in a study investigated the adaptation and performance
of PS bacteria (three
Bacillus
spp. and two
Pseudomonas
spp.) in conditions of high
total P content in soil employing three experiments. In the first experiment, the PS
potential of the
Bacillus
and
Pseudomonas
species was determined under fully
controlled conditions on several growth media treated with different rates and
forms of insoluble P [(FePO
4
, AlPO
4
) or (Ca)
3
(PO
4
)
2
]. All PS bacterial strains
survived and proliferate and could solubilize P even after 14 days of incubation. In
the second experiment, the same bacterial species were inoculated in pure quartz
sand amended with a nutrient solution, and P was added separately in an insoluble
form, as Fe-P, Al-P, or Ca-P. The extractable ammonium lactate ranged from 3.2
to 6.9 and 29 to 40.7 mg kg
1
sand for the insoluble Al-P and Fe-P treatments,
respectively.
Pseudomonas putida
and
B. brevis
performed best as PSB at high P
