Different Response of Silicate Fertilizer Having Electron Acceptors On Methane Emission in Rice Paddy Soil Under Green Manuring.

Cultivation of green manure plants is strongly recommended to improve rice paddy soil properties during non-cropping season. However, green manure could largely increase green house gas emission, in particular methane (hereafter, CH₄) under the flooded rice cultivation system, and therefore, chemical amendments having electron acceptors could be an effective mitigation strategy in CH₄ emissions from irrigated rice (Oryza sativa L.) field. To investigate the effect of iron slag silicate fertilizer (hereafter, silicate fertilizer), which is a byproduct of steel manufacturing and proved as effective soil amendment on reducing CH₄ emission as well as increasing rice productivity, in green manure amended paddy soil, the aboveground biomass of Chinese milk vetch (hereafter, vetch) was amended at the rate of 0, 10, 20 and 40 Mg ha^-1 on fresh weight and then applied silicate fertilizer with the rate of 0 and 2.3 Mg ha⁻¹. Silicate fertilization reduced seasonal CH₄ flux by ca. 14.5 % in the control treatment, as well as ca. 15.7% of rice yield increase. However, this alkaline silicate fertilizer did not properly control CH₄ emission in vetch applied soil, rather than dramatically increased CH₄ production, in particular at the initial rice growing stage. It is probably caused by boosted microbial activity by silicate fertilizer’s liming effect. Conclusively, silicate fertilizer is not suitable as a soil amendment on reducing CH₄ production under highly green manure amended rice paddy, and then should be carefully controlled.