Impact of Nitrogen Fertilizers on Methane Flux to the Atmosphere from the Paddy Ecosystems

Abstract

Methane (CH₄) is an important greenhouse gas in the atmosphere. Among the major sources of methane emission, including, but not limited to, the paddy field, natural swamp, termite, gas leakage, ruminant animal, urban garbage disposal, etc., the paddy fields have been identified as one of the major contributor. In this study, the impact of nitrogen fertilizers on methane fluxes from paddy ecosystems were measured during different growth stages of rice plants. The average CH₄ flux rates from urea amended rice microcosm increased from 16.0 mg m⁻² d⁻¹ at the time of transplantation to 98.6 mg m⁻² d⁻¹ during reproductive stages and finally declined to 48.4 mg m⁻² d⁻¹ at the harvesting stage of the crop. The mean seasonal integrated flux was found to be 3.21 ± 1.31 g m⁻². In Acetobacter amendment, the average CH₄ flux rates increased from 14.4 mg m⁻² d⁻¹ at the time of transplantation to 79.60 mg m⁻² d⁻¹ during reproductive stages and finally declined to 36.5 mg m⁻² d⁻¹ at the harvesting stage of crop. In both the amendments, two peaks in CH₄ activity namely, one at the tillering stage and the other at the reproductive stage of the crop were observed. The Acetobacter amendment resulted in significant reduction of CH₄ emission by 19.2 % as the inoculation of rice roots with acetobacter resulted in high O₂ concentration in the rhizosphere by enhancing cell wall permeability caused by phytohormone (IAA) released by the bacteria.