No lesser evil

By Savvy Soumya Misra
Published: Wednesday 15 October 2008

Slulphate excess can harm soil Controlling methane emissions through acid rain?

adding sulphate to soil in paddy fields is a popular method of controlling methane emission, to the tune of up to 70 per cent. In highly polluted countries such as India and China, acid rain also deposits a substantial amount of sulphate. This leads to more than required sulphate, which can be harmful for paddy. In such cases it becomes imperative to use sulphate sparingly, says a new study published in the August issue of the Journal of Geophysical Research.

Vincent Gauci of the Department of Earth and Environmental Sciences, Open University, Milton Keynes, uk, simulated acid rain conditions and used it to reduce ghg emissions from paddy. He found that the emissions reduced by 24 per cent during grain filling and the ripening stages of rice, which account for half the methane emissions in the cultivation period. When an equal amount of sulphate (deposited by acid rain) was added, it reduced methane emission by 43 per cent.

"It is a known fact that sulphate is used to retard methane emissions but the paper overlooks several factors. Both India and China are major paddy producers but the research has set acidrain levels in China as its benchmark. The levels in India are much lower and hence is not applicable here," explains C Sharma of National Physical Laboratory, New Delhi.

He adds that methane formation and its emissions are high where the soil is rich in organic carbon. "In India, the soil is poor in carbon. Moreover, since the research has been conducted only on the root system it fails to study the effect of acid rain on the leaves and the final crop. Besides, acid rain is disastrous for the ecology." The research has also been criticized for being just an observation without going a step ahead to examine the impact of acid of cultivar. Sharma suggests that methane emissions could be controlled by proper water management and better drainage system in the rain fed areas.

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