76
S. Ambreetha et al.
than the rate required for highest yield attributes [48]. Analysis of bacterial community structure in long term fertilized paddy soil, continuously supplied with N fertilizers for past 4 decades concluded that certain beneficial bacterial phyla (Proteobacteria, Acidobacteria and Cyanobacteria) were suppressed, severely affecting soil
biogeochemical cycling and rice productivity [56]. Availability of N in soil exerts
indirect control over C allocation, paddy rhizodeposits and their uptake by microbiome [33]. Foresaid information warns about the negative effect of excessive N
fertilization over C sequestration in paddy soil apart from environmental pollution.
Additionally, frequent input of nitrogen fertilizers and their sedimentation in wetland
ecosystem predominantly arrests the growth of nitrogen-fixing bacteria and subsequently reduces the nitrogen fixing rate. This process could alter the source of nitrogen
for vascular plants in wetland ecosystem that otherwise depends on N fixed by the
microbes into their root system [66]. As N input could significantly alter both N and
C cycling in paddy ecosystem, cautioned application of optimum dose of fertilizers
would help to maintain a healthy biogeochemical cycle along with stable microbiome
and sustainable crop yield.
7 Soil Health and Sustainability
N fertilization effect on rice paddies were much focused on their relation with yield
and productivity. Their application is not only correlated with their improvement
in crop yield, but also has indirect effect on soil physical, chemical and biological properties. Thereby the sustained uses ultimately have pronounced effect on
quality and fertility of the soil [116]. The inappropriate usage results in volatilization, leaching, decreased nitrogen use efficiency and so on. Alam and Jia [1] have
elucidated the enhanced nitrification activity upon application of urea and ammonium
sulphate. Similar results were shown by Verhamme et al. [99] with positive correlation between nitrification activity and ammonium concentration. Atere et al. [3] have
observed the interaction effect of N fertilizer and water regime which has effect on
rice shoot biomass and photosynthates. They have also hypothesized the stabilized
C rhizodeposition upon N treatment in alternate wetting and drying. The assimilate
deposition is enhanced in silt and clay fractions, microaggregates and macroaggregates of rhizosphere. Optimizing N fertilization with suitable management practices
helps to augment C sequestration. Jiang et al. [46] have studied the positive correlation between GHG emission and applied N fertilizer. Increased carbon footprint
was observed due to increased N fertilizer rate. However peak emission of methane
were found in medium N application which gradually decreased with higher N. Optimizing N fertilizer input, not only serves as a significant strategy for mitigation of
GHG emissions, but also in reducing carbon footprint. Mineralization of N and C
strengthen soil fertility and sustainability by various geochemical processes that are
triggered by inorganic N [51]. Hence a wide-ranging knowledge on transformation of
S. Ambreetha et al.
than the rate required for highest yield attributes [48]. Analysis of bacterial community structure in long term fertilized paddy soil, continuously supplied with N fertilizers for past 4 decades concluded that certain beneficial bacterial phyla (Proteobacteria, Acidobacteria and Cyanobacteria) were suppressed, severely affecting soil
biogeochemical cycling and rice productivity [56]. Availability of N in soil exerts
indirect control over C allocation, paddy rhizodeposits and their uptake by microbiome [33]. Foresaid information warns about the negative effect of excessive N
fertilization over C sequestration in paddy soil apart from environmental pollution.
Additionally, frequent input of nitrogen fertilizers and their sedimentation in wetland
ecosystem predominantly arrests the growth of nitrogen-fixing bacteria and subsequently reduces the nitrogen fixing rate. This process could alter the source of nitrogen
for vascular plants in wetland ecosystem that otherwise depends on N fixed by the
microbes into their root system [66]. As N input could significantly alter both N and
C cycling in paddy ecosystem, cautioned application of optimum dose of fertilizers
would help to maintain a healthy biogeochemical cycle along with stable microbiome
and sustainable crop yield.
7 Soil Health and Sustainability
N fertilization effect on rice paddies were much focused on their relation with yield
and productivity. Their application is not only correlated with their improvement
in crop yield, but also has indirect effect on soil physical, chemical and biological properties. Thereby the sustained uses ultimately have pronounced effect on
quality and fertility of the soil [116]. The inappropriate usage results in volatilization, leaching, decreased nitrogen use efficiency and so on. Alam and Jia [1] have
elucidated the enhanced nitrification activity upon application of urea and ammonium
sulphate. Similar results were shown by Verhamme et al. [99] with positive correlation between nitrification activity and ammonium concentration. Atere et al. [3] have
observed the interaction effect of N fertilizer and water regime which has effect on
rice shoot biomass and photosynthates. They have also hypothesized the stabilized
C rhizodeposition upon N treatment in alternate wetting and drying. The assimilate
deposition is enhanced in silt and clay fractions, microaggregates and macroaggregates of rhizosphere. Optimizing N fertilization with suitable management practices
helps to augment C sequestration. Jiang et al. [46] have studied the positive correlation between GHG emission and applied N fertilizer. Increased carbon footprint
was observed due to increased N fertilizer rate. However peak emission of methane
were found in medium N application which gradually decreased with higher N. Optimizing N fertilizer input, not only serves as a significant strategy for mitigation of
GHG emissions, but also in reducing carbon footprint. Mineralization of N and C
strengthen soil fertility and sustainability by various geochemical processes that are
triggered by inorganic N [51]. Hence a wide-ranging knowledge on transformation of