Abstract
Rice fields are significant contributors of greenhouse gases mainly methane and nitrous oxide to the atmosphere. Increasing concentrations of these greenhouse gases play significant role in changing atmospheric chemistry such as mean air temperature, rainfall pattern, drought, and flood frequency. Mitigation of greenhouse gases for achieving sustainable agriculture without affecting economical production is one the biggest challenge of twenty first century at national and global scale. On the basis of published scientific studies, we hereby assess the use of nitrification inhibitors for greenhouse gas mitigation from rice soil. Biologically oxidation of ammonium to nitrate is termed as nitrification and materials which suppress this process are known as nitrification inhibitors. Soil amendment by addition of certain nitrification inhibitors such as neem oil coated urea, nimin-coated urea; dicyandiamide, encapsulated calcium carbide, and hydroquinone reduce cumulative methane and nitrous oxide emission from rice. Firstly, these inhibitors reduce nitrous oxide emissions both directly by nitrification (by reducing NH4+ to NO3-) as well as indirectly by de-nitrification (by reducing NO3- availability in soil). Secondly, methane emission from rice soil can be reduced by enhancing methane oxidation and suppressing methane production and further by reducing the aerenchymal transportation through rice plant. Application of some of the nitrification inhibitors such as calcium carbide and encapsulated calcium carbide reduce methane production by releasing acetylene gas which helps in reducing the population of methanogenic microbes in the soil. Application of nitrification inhibitors also helps to maintain soil redox potential at higher level subsequently reducing cumulative methane emission from soil. Plant derived organic nitrification inhibitors (neem oil, neem cake, karanja seed extract) are eco-friendly and possess substantial greenhouse gas mitigation potential from rice. In the current scenario of global warming and environmental pollution, application of organic plant derived nitrification inhibitors is much needed for sustainable agriculture.
Highlights
Global climate change is one of the biggest challenges of the twenty first century
Rise in atmospheric greenhouses gases (GHGs) such carbon di-oxide, methane (CH4), chlorofluorocarbon and nitrous oxide (N2O) concentration in atmosphere due to anthropogenic activities leads to global warming (IPCC 2007)
Nitrogen base fertilizer are main sources of N2O production in rice soil and about 1.25 % of the total applied nitrogen is converted into atmospheric N2O (Bouwman 1994) under aerobic condition in soil but under flooded rice less than 0.1 % of applied N fertilizer is emitted as N2O (Freney et al 1997)
Summary
Global climate change is one of the biggest challenges of the twenty first century. Enhance greenhouses effect lead to rise in mean global air temperature and it is projected that mean temperature may increases from 1.5 to 4.5 oC by the end of 21st century (IPPC 2013). Rise in atmospheric greenhouses gases (GHGs) such carbon di-oxide, methane (CH4), chlorofluorocarbon and nitrous oxide (N2O) concentration in atmosphere due to anthropogenic activities leads to global warming (IPCC 2007). In this review study we develop understating of NI in rice soil to mitigate GHGs emissions to combat global warming issues. Methane and nitrous oxide mitigation potential of nitrification inhibiters in rice Biological oxidation of ammonium to nitrate through nitrite by nitrifying bacteria species Nitrosomanas and Nitrobacter respectively is known as Nitrification and material which retard or inhibit nitrification process termed as Nitrification inhibitors (NI) ( Hussian et al 2015; Saharwat 2004). In current scenario of global warming application of NI for reducing greenhouse gases emissions such as N2O and CH4 from rice soil have good environmental sound as this compound reduce nitrate water pollution load .
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