Current World Environment

Introduction

Methane (CH₄) atmospheric concentration has significantly rises due anthropogenic activity. Graedel and McRae¹ presented first evidence that atmospheric concentration of CH₄ is increasing. In agriculture submerged rice (Oryza sativa L.) soils are the major source of CH₄ emission to atmosphere. Rice is second most consumed cereal in world after corn and out of total rice 90% is cultivated in Asia under irrigated conditions. Under continues standing water soil redox potential (Eh) drops sharply within few days and leads to process methanogenesis in soil.² In methanogensis, soil archaea methanogens degraded organic matter and produce CH_4.³ CH₄ emission from rice soil is a net balance of production by methanogens in reducing environment after oxidation by methanotrophs in oxidizing environment and it is influenced by several factors such as water conditions, Eh, soil temperature, pH, fertilizer managements, and organic matter.^4-5  Water management’s practices such as alternate drying and wetting, mid-season drainage, system of rice intensification etc were effective tool to reduce CH₄ emission from rice cultivation. Water managements practices have limitation in lowland area were water management is difficult task so there is need for other effective interventions for CH₄ reduction from lowland or continues flooded rice soils. CH₄ is second most potent greenhouse gas after carbon dioxide and it is 25 times greenhouses gas as compared to carbon dioxide.^6-7 According to IPCC⁸ CH₄ contributes 16% of total emissions at global level and out of total rice field alone contribute 10% of total CH₄ emission at global level.⁹ Kumar et al.,¹⁰ reported that by the end of twenty first century global mean temperature may rise up to 1.5ËšC  due to raise in global greenhouses gases atmospheric concentrations. Global warming is major concerned of 21^st century for scientific and policy maker.  As the world population was increasing so under such scenario CH₄ mitigation from rice field needed without having any negative impact on rice production. Rice production depends on type and amount of nitrogen (N) based fertilizer applied for cultivation. N based fertilizer amendments may be used for CH₄ emissions mitigation from the rice soil. Impact of different N based fertilizer on CH₄ emission is less elevated so it is needed. The objective of this field experiment is to evaluate the impact of nitrogen fertilizer on CH₄ emissions from rice soil under continuous flooded condition.

Material and Methods

Site Descriptions

Field experiment was carried out at the research farm of Indian Agricultural Research Institute, New Delhi, India, during kharif cropping season of year 2015 (Fig. 1).The climatic condition of the region was sub-tropical, semi arid that was characterized by dry winter and maximum rainfall occurs during from June to September of year (Fig. 2).The soil in study site was sandy loam in texture and pri-transplanting physicochemical of experimental site soil are mentioned in Table (1).

Figure 1: Experimental site of Indian Agricultural Research Institute, New Delhi, India Click here to View figure

Figure 2: Metrological data of experimental site Click here to View figure

Table 1: Pri-transplanting physicochemical properties of the experimental site

Experimental design and treatments details

The experiments consist of three treatments with three replicate each which are arranged in RBD. Composition and dose of various treatments were mentioned in Table (2). Pusa Basmtai 1509 variety of rice (Oryza sativa L.) was adopted for conducting the experiment.  Two to three rice seedlings (23 days age) were transplanted at 15 x 20 cm spacing. Continuous flooding condition at 8 ± 4 cm water level was maintained by groundwater irrigation for entire cropping period. The field was naturally allowed to dry three weeks before harvesting of crop. No chemical interventions (pesticide and herbicide) were applied to avoid their additional effects. Weeding in done manual when were required.

Table 2: Different treatments used during rice cultivation

Methane sampling collection and analysis

Gas samples were collected at 7 days regular interval throughout the rice cultivation by manual closed chamber technique.¹¹ Gas samples were collected between 9 am to 11 am and samples were withdrawn from top of the chamber using 20 ml air-tight syringes at 0, 1/2 and 1 hrs. Concentration of CH₄ gas in the collected gas samples were measured by using gas chromatography equipped with column and a flame ionization detector.

Result and Discussion

Methane emission among all treatments was low during first three weeks and significantly increased with plant growth and lower soil Eh. The highest flux peak was observed at 35 days after transplanting (DAT) and second peak occur at 63 DAT (Fig 1).

Figure 1a: Methane emissions from rice soil under different nitrogen based fertilizer amendments Click here to View figure

Two higher CH₄ peaks may be due to degradation of soil organic matter by methanogens bacteria under anaerobic conditions and similar flux were also reported by¹² in rice soil. The cumulative seasonal CH₄ flux was 35.2 kg ha^-1 under the control treatment The highest cumulative CH₄ flux was recorded in urea (36.3 kg ha^-1) treatment followed by control (35.2kg ha^-1) and ammonium sulfate (28.3 kg ha^-1). As compare to control, urea fertilizer application enhances CH₄ emissions by 2.72% and ammonium sulfate amendments reduce CH₄ emissions by 19.5% as compared to control (Fig. 2). Ammonium sulfate application mitigates total seasonal CH₄ emissions by 21.6% over to urea (Fig. 2).

The higher CH₄ emission under nitrogen applied plots over no nitrogen amendments has been reported.¹³ Urea application enhances the ammonium ions concentration in soil and due to structural symmetry between CH₄ and ammonium ion³ methanotrophs bind with ammonium ions instead of CH₄ therefore results in less CH₄ oxidation by methanotrophs in soil which final result in higher CH₄ emission from soil.¹⁴

Minami¹⁵ observed about more than 15% reduction in average CH₄ flux from rice soil by soil incorporated with ammonium sulfate at 200 kg N ha^-1 rate as compared to 200 kg N ha^-1 urea incorporation. Similar finding were also observed by Ali et al.,¹⁶ and they reported 16% and 21% reduction in total seasonal CH₄ flux by ammonium sulfate over urea in upland and lowland rice soil in Bangladesh respectively. On ammonium sulfate ions soil concentration of active sulfate ions increases¹⁶ which result in higher population of sulfate reducing bacteria in soil. Sulfate reducing bacteria compete with methanogens bacteria for organic matter as they both feed on similar substrate⁵ therefore on application of ammonium sulfate suppressed methanogens activity in soil which result in CH₄ flux reduction form rice soil.

Figure 2a: Cumulative seasonal methane emissions from  rice soil alone with methane reduction in percentage Click here to View figure

Conclusions

In is field study we evaluate the impact different nitrogen based fertilizer impact on methane emission from paddy soil.  A total cumulative methane emission was highest in urea applied plots and lowest in ammonium sulfate plots. Ammonium sulfate application reduces 19.5% and 21.6% as compare to urea and control respectively. Therefore, based on this field study data it could be suggested that application of ammonium sulfate significantly reduce methane from rice soils.

Acknowledgements

We thank the Director, Dean and PG School of Indian Agricultural Research Institute (IARI), New Delhi for providing all facilities required in this study. Financial support to Mr. Sandeep K. Malyan during Ph.D as UGC-JRF/SRF provided by University Grant Commission (UGC), New Delhi Government of India is gratefully acknowledged.

References
 

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