Previous Year Question

Rice fields are important anthropogenic agricultural sources of both methane and nitrous oxide.

When rice fields remain flooded for long periods, the oxygen present in soil pores is exhausted and anaerobic conditions develop.

Under these anaerobic conditions, methanogenic microorganisms decompose organic matter and produce methane (CH₄).

Rice plants possess specialised tissues for the movement of air, known as aerenchyma. Methane produced in the soil can reach the atmosphere through these tissues.

Some methane also reaches the atmosphere through soil bubbles and irrigation water.

Incorporation of rice straw, manure and other organic materials into flooded fields provides additional organic matter to microorganisms and may increase methane production.

The application of nitrogenous fertilizers and the processes of nitrification and denitrification occurring in the soil can produce nitrous oxide (N₂O) in rice fields.

The availability of oxygen keeps changing when a field undergoes wetting and drying. This change affects both nitrification and denitrification processes.

Reducing continuous flooding and adopting alternate wetting and drying can reduce methane emissions, but balanced management of water and nitrogen is also necessary to control nitrous oxide.

Cotton, sugarcane and wheat cultivation may release nitrous oxide due to the use of nitrogenous fertilizers, but their fields generally do not remain flooded for long periods like rice fields.

Therefore, methane production from these crops is much lower than that from flooded rice fields.

Methane and nitrous oxide are both powerful greenhouse gases. Proper management of water, fertilizers and organic materials is therefore important in rice cultivation.