Abstract

Five inorganic materials (steel slag, silica gel, electric furnace slag, fly ash and Japanese silica fertilizer) and six organic materials (rice husk-biochar, rice straw compost, media of mushroom, cacao shell-biochar, rice husk-ash and elephant grass), were evaluated as Si fertilizer sources for rice plants (Oryza sativa L.) in two soil types (red clayey and sandy soil). Evaluation was carried out by incubating them at 30^oC under submerged condition for 70 days. The soil solution was replaced at day 7, 14, 21, 42, 49, 56, 63 and 70 and the amount of silicon (Si) release, pH, Eh, calcium (Ca), magnesium (Mg), iron (Fe) and manganese (Mn) concentrations in soil solutions were determined. The amount of Si release ranged from n.d. (not detected)-32444.7 mg Si kg^-1 and 105.84-48524.0 mg Si kg^-1 in red clayey and sandy soil solutions, respectively during 70 days of incubation. Reduction in soil Eh was accompanied with an increase in the solubility of the soil Si especially for silica gel, electric furnace slag, elephant grass and media of mushroom. Higher exchangeable Ca content in soil tended to suppress Si release from rice straw compost, rice husk-ash and cacao shell-biochar. Considering the results of present study and availability of the materials, we concluded that steel slag of the inorganic materials and rice straw/husk and cacao shell-biochar of organic materials had the highest potential as Si fertilizer source in Indonesia.

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