Studies on DIEL Variation of Methane Fluxes from Rice Paddy Ecosystems of South India

Wet land rice paddy ecosystems have been recently identified as a major source of atmospheric methane, which is currently increasing at 7 ppbv yr^-1. Methane emission form rice paddies indicate a global source of 60 Tg yr^-1. The CH₄ emission rates vary significantly with the types of soil, cultivar variety, and cultivar age and water management. The expansion of irrigated cultivation area and new cultivation practices have made rice fields one of most important anthropogenic sources for atmospheric CH₄. The CH₄ emission from paddy ecosystems is controlled by physical processes (diffusion, ebullition and ventilation) and biological processes (microbial production and consumption). Thus in an effort to reduce uncertainties, in the present study diel variation of methane fluxes were measured from control, Pseudomonas and nemento amended rice cores for 24 hours at an interval of 30 minutes during tillering, reproductive and harvesting stages of growth of rice plants. The CH₄ emission rates increased at accelerated rates and were maximum during the early afternoon (14-15 hours, 2.59-9.35 mg/m²) and decreased rapidly and remained constant during night (8.19-7.71 mg/m²). The diel CH₄ emission in all the rice cores were lower during the tillering stage (2.18-7.17 mg/m²) and higher at the reproductive stage of the plant (2.59-9.50 mg/m²). This is probably due to higher soil Eh during the initial stage of plant growth. The methane emission was lower in night because low soil temperature at night causes low CH₄ production rates. Also higher ambient CO₂ concentration in the canopy during night reduces the transport of CH₄ through plants. The CH₄ emission rates decreases in Nemento amended cores (6.35 mg/m²) than Control cores (8.41 mg/m²) as nemento (product from neem) being nitrification inhibitor reduces CH₄ production in soil. The Pseudomonas amended cores resulted in less CH₄ emission (6.9 mg/m²) than Control cores as pseudomonas being a denitrifying bacteria helps reducing CH₄ emission.