Current World Environment

Introduction

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 21^st 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). According to IPCC (2014) carbon di-oxide (Fossil fuel and industrial processes), Carbon di-oxide (Forestry and other land use), CH₄, N₂O and fluorinated gases contributes 65 %, 11 % , 16%, 6%  and 2 % respectively at global level in 2010 (Figure 1). Methane and nitrous oxide are two major GHGs emitted from rice (Oryza sativa L.) agro-ecosystem.  At global level rice cultivation alone contribute 10 % of total CH₄ emission (GMI 2011) while the global warming potential of N₂O is 298 times higher (Rees et al. 2013) than carbon di-oxide, so mitigation of both CH₄ and N₂O is needed to combat global warming. There are mainly four different types of rice ecosystem namely upland, rainfed, irrigated and deer rice ecosystem (Adhya et al. 2014). Deep rice and irrigated rice ecosystem are main sources of CH₄ emissions to atmosphere will upland and dry period in between continuous flooded are main sources of N₂O emissions to atmosphere from rice soil. In deep and continuous irrigated rice anaerobic conditions lead to sharp decline in soil redox potential (Ali et al. 2015; Hussain et al. 2015; Dubey 2005) which results in CH₄ production. In flooded rice methanogens bacteria consume soil organic carbon and emit CH₄ (Nazaries et al. 2013; Penning and Conrad 2007). Methane produce by methanogens in rice soil, generally emits to atmosphere by three (diffusion, ebullition and aerenchymal transportation) possible mechanisms (Green 2013; Tokida et al. 2013; Das and Baruah 2008; IPCC 1996; Neue 1993). In rice soil N₂O is produce by both biological (nitrification and denitrifcation) and chemical decomposition process (Lan et al. 2014; Baggs 2011; Ussiri and R. Lal 2007; Freney 1997; Bremner 1997). 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). Methane and N₂O production is rice soil is effect by several factors such as water managements, soil pH, redox potential, temperature, soil matter of the soil, soil microorganisms diversity, transplanting methods, rice cultivar, Crop duration and type of time of fertilizer application (Hussain et al. 2015; Hadi et al. 2010; Conrad 2007; Dubey 2005; Conrad 2002, Le Mer and Roger 2001). The nitrification inhibitor play potent role in mitigating GHGs emissions from different rice argo-ecosystem. In this review study we develop understating of NI in rice soil to mitigate GHGs emissions to combat global warming issues.

Figure 1: Percentage contribution of various anthropogenic  greenhouse gases emissions at global level in 2010 (IPCC 2014)  Click here to View figure

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 also reduce nitrate water pollution load also. NI reduces N2O emission directly by retarding nitrification in soil and by reducing availability of nitrate for de-nitrification indirectly. Several studies revels that application of NI such as dicyandiamide ( Hussain et al. 2015; Datta and Adhya 2014; Linquist et al. 2012; Li et al. 2009; Pathak et al. 2003), urease ( Hussain et al. 2015; Majumdar et al. 2003), hydroquinol (Li et al. 2009) and thiosulphate (Malla et al. 2005) can mitigate CH₄ emission from rice soil. Similarly, several previous studies reports that nitropyrimidine (Majumdar et al. 2003), dicyandiamide (Datta and Adhya 2014; Linquist et al. 2012; Li et al. 2009; Pathak et al. 2002), benzoic acid (Majumdar et al. 2003) nimim (Datta and Adhya 2014) and thiosulphate (Malla et al. 2005; Kumar et al. 2000) have significant N₂O reduction potential in rice soil (Table 1).

Li et al. (2009) have reported that combined basal application of HQ/DCD reduces CH₄ emissions by 35.38 %. In combination the application of HQ and DCD at tillering and panicle initiation stage reduces CH₄ emission by 19.04 and 12.24 % respectively as compare to control in rice soil (Li et al. 2009). Malla et al. (2005) reported that organic plant- derived neem oil coated urea reduce total CH₄ by 7.78 % from rice as over inorganic fertilizer (urea) application along (Table 1).  Inorganic NI such calcium carbide coated urea and DCD reduces total emissions by 13.33 and 11.85 % than control (urea) respectively from paddy cultivation (Malla et al. 2005). In field experiment conducted at research farm of Indian Agricultural Research Institute, Pathak et al. (2003) observed that DCD along with urea reduce total cumulative CH₄ emission from 21.3 kg ha^-1 to 14.9 kg ha^-1 which show that DCD application along with urea mitigate 30.5 % of total emission as compare to control (urea). In laboratory study conducted by Xu et al. (2002) observed that HQ (132.97 mg CH₄ pot^-1) and DCD (132.97 mg CH₄ pot^-1) amendment alone and in combination (89.22 mg CH₄ pot^-1) were effective for reducing CH₄ emissions as compare to control (190.26 mg CH₄ pot^-1). Bharti et al. (2000) invested impact of six different NI on CH₄ production and observed that all the compound reduce mean CH₄ production. Mean CH₄ production from control (1204 μg kg^-1 soil) is reduce to 380, 941, 908, 634, 1065 and 1060 μg kg^-1 soil by sodium azide, aminopurine, pyridine, thiourea and ammonium thiosulfate respectively(Table 1). Datta and Adhya (2014) observed that organic NI such as nimim and karanjin are most effective for reducing N₂O emission in rice as campare to inorganic NI DCD and prilled urea. Nimim reduce total N₂O emission by 69.38 % were as karanjin to reduce N₂O emission by 38.13 % as compare to prilled urea (Table 1).  In other field experiment Malla et al. (2005) also observed.

Table 1: Influences of different nitrification inhibiters on GHGs emission in rice soil

(-) More emission; M- mitigation, NA-not applicable, * mg CH₄ pot⁻¹, **mg N₂O-N pot⁻¹

That organic NI neem cake and neem oil coated urea reduce N₂O emsiion by 10.53 % and 21.05 % than control (urea). In similar study Malla et al. (2005) reported that HQ, DCD, thiosulpahte along with urea and calcium carbide coated urea mitigate N₂O emission by 3.95, 17.11, 34.21 and 28.05 % as compare to control from rice soil (Table 1). Li et al. (2009) observed that HQ and DCD basal application in rice reduce total cumulative N₂O emission to 3.90 kg ha^-1 as compare to control 3.90 kg ha^-1. HQ/DCD application at tillering and panicle intiation stages of rice reduces N₂O emission by 55.64 and 17.18 % respectively in Chinese soil (Table 1). Pathak et al. (2002) reported that soil amendment by DCD along with urea mitigate N₂O emission by 21.39 % than soil amendment by urea   alone in rice soil. Xu et al. (2002) also observed that HQ, DCD and HQ  plus DCD reduces N₂O emissions to 13.2, 9.14 and 6.51 mg N₂O-N pot^-1 as compare over control (17.25 mg N₂O-N pot^-1) respectively.

Conclusion

The increasing trend of human population in Indian and at global level creates treamdmous pressure on agricultural system for feeding. This demand leads to evolution of modern agriculture and rice is important stable food for majority of population in world. Rice production is major source for greenhouse gases emission which leads to global warming.  In this study we synthesized the published data to provide suitable rice management for greenhouses mitigation by fertilizer management (Nitrification inhibitors). We found that nitrification inhibitors interventions in rice can be one effective tool to anticipate global warming.  For instances, inorganic nitrification inhibitors such DCD, HQ and thiosulphate application have methane and nitrous oxide mitigation potential from rice cultivation. Recently the mitigation potential of few organic nitrification inhibitors such as karanjin, nimim and neem oil coated urea was also explored. Fertilizer management practices like nitrification inhibitors application sound environmental friendly and help in achieving sustainable agricultural goal.

Acknowledgements

Author is thankful to Head of the Division (Dr. S.D Singh) Center for Environment Science and Climate Resilient Agriculture, Indian Agricultural Research Institute, New Delhi-10012, India, for all support and encouragement.

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