N Fertilization Dependent Bacterial and Archaeal …
67
elucidated ammonification which comprises of oxidative and reductive deamination
of amino acids operative under oxidized and reduced soil layers, respectively. This
reaction secretes part of ammonia into soil solution while the remaining into adsorbed
phase where there is a dynamic equilibrium occurs between them. Ponnamperuma
[72] have elucidated the portion ammonia in the solution phase depends on organic
matter and texture of the soil. Their rate is comparatively higher in the former and
even influenced by certain parameters like pH, temperature, C: N ratio, soil moisture and organic matter status. Anaerobic condition is marked by accumulation of
ammonium, nitrate instability which ultimately leads to lowered N requirement for
decomposition of organic matter. However, the degree of mineralization is rapid
under warm temperature,the soil water content is insensitive. Under elevated CO 2
and temperature, the presence of higher C substrates with labile N pools in rhizosphere positively influenced the N mineralization [7]. Apart from this, the labile N
pools including microbial biomass N, ammoniacal N and nitrate N were significantly
higher under elevated CO 2 and temperature than that of ambient conditions. Ammonium—N accumulates in reduced conditions notably on the soil with high organic
load, while on the other hand in soil with lower organic matter ammonium is rapidly
converted to nitrite and further to nitrate. Until when rice roots uptake or losses occur,
NH 4
+ -N remains stable under reduced conditions and retains as cations and converted
into cations upon the exposure of oxygen. Ammonia volatilization is considered as
major N loss and receives considerable attention for their mitigation. He et al. [39]
have observed high flux of ammonia volatilization in the absence of water table.
They are regulated by properties of flooded water such as pH and temperature. These
results were similar to the study conducted by Hayashi et al. [38], suggesting their
loss could be handled with appropriate management practices.
2.1.2 N Immobilization
The balance between nitrogen immobilization and mineralization is the driving factor
for the availability of N required for plant uptake [23]. The equilibrium between
them is influenced by various factors such as oxygen status, temperature, moisture
and organic material and C:N ratio. It is one of the most critical steps influencing the
long term fertility of the soil. Reduced fertilizer use efficiency upon their application
sets step for N losses with greater degree of immobilization. The higher extent of
immobilization paves way for low N fertilizer use efficiency. Immobilization takes
route viz., microbial biomass, amino acids and amino sugars [67]. They are further
remineralized into fractions of soil organic matter. Anaerobic conditions prevailing
under paddy cultivation immobilize greater N from the biomass. The rate of N immobilization further increases upon rice straw incorporation suggesting the importance
the crop residue and irrigation management practices in N immobilization [79]. In
depth acquaintance on biological control on various route of immobilization would
facilitate better utilization of N from crop residues and fertilizers.
67
elucidated ammonification which comprises of oxidative and reductive deamination
of amino acids operative under oxidized and reduced soil layers, respectively. This
reaction secretes part of ammonia into soil solution while the remaining into adsorbed
phase where there is a dynamic equilibrium occurs between them. Ponnamperuma
[72] have elucidated the portion ammonia in the solution phase depends on organic
matter and texture of the soil. Their rate is comparatively higher in the former and
even influenced by certain parameters like pH, temperature, C: N ratio, soil moisture and organic matter status. Anaerobic condition is marked by accumulation of
ammonium, nitrate instability which ultimately leads to lowered N requirement for
decomposition of organic matter. However, the degree of mineralization is rapid
under warm temperature,the soil water content is insensitive. Under elevated CO 2
and temperature, the presence of higher C substrates with labile N pools in rhizosphere positively influenced the N mineralization [7]. Apart from this, the labile N
pools including microbial biomass N, ammoniacal N and nitrate N were significantly
higher under elevated CO 2 and temperature than that of ambient conditions. Ammonium—N accumulates in reduced conditions notably on the soil with high organic
load, while on the other hand in soil with lower organic matter ammonium is rapidly
converted to nitrite and further to nitrate. Until when rice roots uptake or losses occur,
NH 4
+ -N remains stable under reduced conditions and retains as cations and converted
into cations upon the exposure of oxygen. Ammonia volatilization is considered as
major N loss and receives considerable attention for their mitigation. He et al. [39]
have observed high flux of ammonia volatilization in the absence of water table.
They are regulated by properties of flooded water such as pH and temperature. These
results were similar to the study conducted by Hayashi et al. [38], suggesting their
loss could be handled with appropriate management practices.
2.1.2 N Immobilization
The balance between nitrogen immobilization and mineralization is the driving factor
for the availability of N required for plant uptake [23]. The equilibrium between
them is influenced by various factors such as oxygen status, temperature, moisture
and organic material and C:N ratio. It is one of the most critical steps influencing the
long term fertility of the soil. Reduced fertilizer use efficiency upon their application
sets step for N losses with greater degree of immobilization. The higher extent of
immobilization paves way for low N fertilizer use efficiency. Immobilization takes
route viz., microbial biomass, amino acids and amino sugars [67]. They are further
remineralized into fractions of soil organic matter. Anaerobic conditions prevailing
under paddy cultivation immobilize greater N from the biomass. The rate of N immobilization further increases upon rice straw incorporation suggesting the importance
the crop residue and irrigation management practices in N immobilization [79]. In
depth acquaintance on biological control on various route of immobilization would
facilitate better utilization of N from crop residues and fertilizers.