Effects of iron-containing materials on reducing paddy rice root-rot and suppressing methane emission with dry sludge application
2023
Kusaka, H. | Unagami, S. | Inagaki, K. | Inubushi, K. | Kato, T. | Oshima, H.
When fresh organic matter, such as dried sludge, is fertilized just before flooding in paddy rice cultivation, the soil becomes abnormally reduced conditions, then produces methane gas and root rot due to hydrogen sulfide generation. In this study, the amount of methane gas generated and the effect of reducing root-rot when dried sludge and iron-containing materials were used in combination in pot experiments was compared. De-phosphorized slag, converter slag, and ferrous materials were used as iron-containing materials and applied to river sand and gray lowland soil (1:1). The treatments consisted of 1) chemical fertilizer plot, 2) sludge plot applied with dried sludge only, and 3) combined sludge-ferrous material plot. Rice was grown for 3 months. The degree of hydrogen sulfide generation, soil Eh and methane gas emission were measured from the beginning of cultivation, and the degree of root-rot was examined at harvest. Authors also measured the amount of ferrous in the soil after 1, 2 and 3 months of transplanting and the amount of free iron in the soil after harvest. The degree of hydrogen sulfide generation was enhanced in all the plots where dried sludge was applied, and there was no difference in the degree of root-rot caused by the application of each iron-containing materials. The combined use of iron-containing materials reduced methane emission. Free iron and ferrous were highest in the de-phosphorized slag combined plot. The amount of ferrous reached a maximum 2 months after transplanting in each slag combination plot. These results suggest that ferrous eluted from iron-containing materials can improve plant growth with dry sludge, and suppress methane emission, and that the de-phosphorized slag is particularly effective among tested materials.
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