Effect of a Fly Ash and Gypsum Mixture on Rice Cultivation

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Paddy soil in Korea generally required the addition of silicate to enhance rice productivity. Even though a silicate fertilizer has been applied at 4-year intervals by the Korean government, the quantity has not been sufficient, due to financial constraints, and an alternative source of cheaper silicate is required. Fly ash, which has a high silicate content, was selected as an alternative in the present study. To improve fly ash, which is highly alkaline and has a high boron content, the material was mixed with a by-product of gypsum (hereafter, described as gypsum) and the pH changes were monitored in water using an incubation test. The initial pH of the water suspension was compatible with the optimum range (ca.6.5-7.0) for rice using a mixture of 75% fly ash and 25% gypsum. A field experiment was carried out to evaluate the productivity of rice (Oryza sativa) on silt loamy soil to which 0 (FG 0), 20 (FG 20), 40 (FG 40), or 60 (FG 60) Mg ha^-1 of the mixture were added. Silicate and lime treatments were selected as a control. The highest rice yield was achieved following the addition of 40 Mg ha^-1 of the mixture to the soil. The mixture of fly ash and gypsum increased the uptake of silicate and phosphate and the amount of exchangeable calcium in the soil. The plant elemental uptake revealed that the application of the fly ash and gypsum mixture did not result in an excessive uptake of heavy metals by the rice in the submerged paddy soil. The amount of available boron increased with the increase in the amount of fly ash up to 0.62 mg kg^-1 following the application of 60 Mg ha^-1 of the mixture, but did not reach toxicity levels for rice, probably due to the dilution and leaching effects under the submerged growing conditions. It is concluded that the fly ash and gypsum mixture could be a good alternative to inorganic soil amendments to restore the soil nutrient balance in paddy soil.
社団法人日本土壌肥料学会の論文

Effect of a Fly Ash and Gypsum Mixture on Rice Cultivation

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