GREEN HOUSE EFFECT DUE TO METHANE FROM PADDY FIELDS
DR. RANJANA*, SURESH KUMAR**
*SAVEN-Govind Ballabh Pant University of Agriculture and Technology,
The occasions gave global concern, one fifths of the over all annual methane emissions which cause greenhouse effect from around the world are from the biogenetic origin. A considerable part of this is attributed to wet land agriculture such as from paddy fields. World population projections indicate that the demand of rice would increase by 50 per cent and for that additional 700 mt of rice will have to be produced, which would increase as much as 20 % methane in atmosphere in next 10 years.
Rice, one of the most important staple crops of the world, is realizing the increased pressure on the growing resources. Area expansion is one of the strategies to meet the growing demand of the population with the increase in crop area, the hazardous effects that rice cultivation brings, are also increasing. Probably, Asia would be most rigorously affected part of the world in the years to come, where 90 percent of rice is grown and consumed. The crop has significant effects on global warming through the emission of greenhouse gas, methane from flooded rice field. This occasion increases atmospheric temperature, resulting in alteration of climate of region. The new environment may replace many of the indigenous species from the area, which may affect the biodiversity of region badly.
Methane is one of the greenhouse gases which induce climatic change, and this phenomenon of modifying climate where atmospheric gases act like glass panes in greenhouses they allow the small wave solar radiation to pass through them but trap the long wave radiation which comes after the reflection from natural bodies. The phenomenon leads to the warming of atmosphere popularly known as “global warming”. It is really a matter of concern that wet land rice agriculture accounts for as much as 265 per cent of anthropogenic methane budget around 70-80 percent of total annual global emission of methane is of biogenic origin and it has been confirmed on the basis of extrapolation of measurements done in Europe and USA, US.EPA. Methane is increasing in atmosphere by around one percent every year. This gas is relatively active trace gas with about 25-30 times more infra red absorption capacity per molecule than carbon di oxide through its atmospheric concentration is about 200 times lesser.
Production of methane is a complicated process that involves specialized anaerobic bacteria methanogens that inhabit flooded soils. In the absence of oxygen, the bacterium produces methane gas. A specific substance in the decomposing organic matter and neutral pH catalyze the methane production. Methane is nothing but end product of anaerobic decomposition of organic matter. This process of anaerobic decomposition occurs in the root zone of plants under flooded soil. The produced gas from root zone is emitted to the environment through the diffusion, ebullition and plant mediated transport. So, rice cultivation is associated with the production of hazardous methane contributing to green house effect and global warming. Western countries say rice growing Asian countries would be responsible for global warming over the next 30 years. From the global perspective point of view, the present paddy production technology has to be examined critically. Various biotic, abiotic and management factors influence methanogens and thus methane released into soil and then into atmosphere. The management factors include soil manipulation, selection of appropriate cultivar, method and time of fertilizer application and water management experiments have established that frequent irrigations with proper drainage strongly reduce irrigation largely suppresses methane emission. However the periods of interruption at flowering stage should be kept shorter to prevent reduction in grain yield. The soil amendments and mineral fertilizers are of prime consideration for application. Addition of iron compounds such as bauxite probably reduces methane emission. The target should be to add electron acceptors in the sequential soil redox reactions.
The addition of sulfate increases the activity of sulfate reducing bacteria, thereby decreasing the activity of methanogens in soil. In nutshell, all efforts should focus to decreases soil solution pH. It is the organic matter, which undergoes anaerobic decomposition to produce methane. Higher dozes of unrecompensed organic matter will increase the methane production. So this practice should be avoided. Deep tillage is good practice to be followed for proper mixing of soil and organic matter and it also increases the content of free iron oxide and easily reducible manganese in the soil because these are accumulated in deeper soil layer due to leaching apart from this, varietals selection is of vital importance. The following points should be kept in mind:- • Varietals selection with low exudation of carbon from roots, • Selection of varieties that have the efficiency of low methane transport and a high methane oxidation in the rhizosphere depending on the specific aerenchyma system in roots and shoots. • Selection of varieties that promise higher harvest index in order to reduce organic matter input into the soil. In conclusion, for India, that is a major grower of paddy in the world, there needs to be a concerted practice of water management approach to curtail methane emission due to wetland farming because greenhouse effect triggers a trail of consequences that have negative impact on overall agriculture and environment. Thus the water management experiments have established that frequent irrigation with multiple drainage strongly reduce methane production in the soil and at flowering stage, reduced irrigation largely suppress methane emission. However the period of interruption at flowering stage should be kept shorter to prevent reduction in grain yield.