Evaluation of silicate iron slag amendment on reducing methane emission from flood water rice farming

Application of electron acceptors such as ferric iron oxides and hydroxides for controlling methane (CH4) emission from wetland rice fields deserves special attention due to its dominant role over all other redox species in wetland soils. Silicate iron slag (hereafter, silicate fertilizer), a byproduct of steel industry containing electron acceptors, was applied in paddy field (Agronomy Farm, Gyeongsang National University, South Korea) at the rate of 0, 1, 2 and 4 Mg ha−1 to investigate their effects on reducing CH4 emissions from flood water rice (Oryza sativa, cv. Dongjinbyeo) farming during 2006–2007. CH4 emission rates measured by closed-chamber method decreased significantly (p < 0.05) with increasing levels of silicate fertilizer application during rice cultivation. Soil redox potential (Eh) showed a contrasting response to CH4 emission rates. The concentrations of dissolved iron materials in percolated water, and the active and free iron oxides in soil significantly increased with the applications of silicate fertilizer, which acted as oxidizing agents and electron acceptors, and eventually suppressed CH4 emissions during the rice growing seasons. Total CH4 emission was decreased by 16–20% with 4 Mg ha−1 silicate fertilizer application and simultaneously rice grain yield was increased by 13–18%. Silicate fertilization significantly stimulated rice plant growth, especially root biomass, root volume and porosity, which might have improved rhizosphere oxygen concentration, and then partially contributed to reduce CH4 emission through enhancing methane oxidation. Therefore, silicate fertilizer could be a good soil amendment for reducing CH4 emission as well as increasing rice productivity in wetland paddy field.