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 30oC 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.
Highlights
Silicon is not recognized as an essential element, but as a beneficial element, Si enhances diseases resistance, alleviates metal toxicity, improves nutrient balance, prevents lodging and enhanced drought tolerance of rice (Ma & Yamaji, 2006)
We recorded that Si release from fly ash in sandy soil solution was less (n.d.-0.03 mmol L-1) than red clayey soil, which Si release was only during the last 14 days of incubation
The Eh in soil solution with additional of steel slag, EFS, JSF, cacao SB, elephant grass and MM markedly decreased after submergence and the maximum negative value of 92.8 mV was observed for soil solution with elephant grass application
Summary
Silicon is not recognized as an essential element, but as a beneficial element, Si enhances diseases resistance, alleviates metal toxicity, improves nutrient balance, prevents lodging and enhanced drought tolerance of rice (Ma & Yamaji, 2006). There is around 102,000,000 ha of acidic soil with Ultisols and Oxisols are the dominant soil beside Entisols, Inceptisols and Spodosols (Subagyo et al, 2000; Mulyani et al, 2009) These soils have been used for rice production in Indonesia. Fly ash from coal combustion where the dust-collection system removes the fly ash from the combustion gases before they are discharged in the atmosphere is high in Si content (Ramezanianpour, 2014) These Si rich materials from industrial wastes are applied to increase soil pH (Haynes et al, 2013). In Indonesia, there are some potential sources as silicate fertilizer from industrial by product and plant material-based silica. The objective of this study is to evaluate Si release from different local materials used as soil fertilizers under submerged conditions in relation with soil chemical properties and other controlling factors
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