Suppression of rice methane production and emission by low dose sulfate application

Gauci, V.; Dise, N. B. and Howell, G. (2006). Suppression of rice methane production and emission by low dose sulfate application. In: American Geophysical Union, Fall Meeting 2006, 11-15 Dec 2006, San Francisco, USA.

URL: http://www.agu.org/meetings/fm06/fm06-sessions/fm0...

Abstract

Large individual applications of SO₄^2-(10²-10³ kg SO₄^2--S/ha) are known to suppress methane emissions from rice paddies by up to ~70%. The application of large quantities of SO₄^2- amendments to rice paddies has therefore been proposed as a greenhouse gas mitigation strategy. In a similar system, natural peatlands, research has established that very low rates of SO₄^2- deposition (~25 kg SO₄^2- -S/ha/yr as small weekly pulses), similar to those of regions experiencing acid rain pollution, suppress methane emissions by as much as 30-40%. It is thought that this is due to stimulation of sulfate-reducing microbial populations that out-compete methane producers for substrates. Given that acid rain S pollution is forecast to increase in Asia, the major rice growing region, we sought to establish the potential for acid rain to suppress CH₄ emission from rice agro-ecosystems by experimentally simulating acid rain inputs of S deposition to rice mesocosms in the laboratory. We used soils from Portuguese rice growing regions as they experience low ambient S deposition, and investigated the effect of simulated sulfate deposition (small regular pulses) on CH₄ emissions, pore- water concentrations of CH₄ and alternate electron acceptors. We also applied an annual dose of S deposition as a single pulse of sulfate to one set of replicate rice mesocosms. After a lag time of 7 weeks, CH₄ emission from the mesocosms subjected to the small weekly applications of ‘acid rain' sulfate as Na₂SO₄ at a rate of 100 kg SO₄^2- -S/ha/yr (amounting to a total deposition of ~20 kg SO₄^2- -S/ha throughout the 10 week experiment) were reduced below the control by an average of 22%, and as much as 35% on a single date. CH₄ emissions from the ‘single pulse' experiment were significantly suppressed by the applied sulfate as were pore-water CH₄ concentrations.

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