Improving methane mitigating functionality of blast furnace slag by adding electron acceptor.

Blast furnace slag (BFS), a byproduct of iron-producing process, has been applied as silicate fertilizer in rice paddy. Silicate fertilizer contains lime and silicate as main components and iron and manganese as electron acceptors. This amendment improves soil productivity and mitigates methane (CH) emissions. However, its suppression effect was limited to <20 % at a field level, and its functionality needs improvement to encourage recycling. We hypothesized that the effect of silicate fertilizer on suppressing CH emission might improve by increasing electron acceptor concentration. To investigate the feasibility of electron acceptor added silicate fertilizer on increasing CH flux suppression, four byproducts of the iron-production process (basic oxygen slag-BOF, ferromanganese slag-FerroMn, iron rust, and Kambara reactor slag-KR) were selected and compared through soil incubation test. Iron rust effectively suppressed CH production by 67 %, which is comparable with a 15-30 % reduction of others. To find the optimum mixing ratio of iron rust, it was mixed to BFS with the rate of 0-5 % (wt wt), and their effect on CH flux was compared. The 3 % mixing ratio highly increased the BFS functionality on suppressing CH production. To confirm the field adaptability of the improved BFS, three types of silicate fertilizer (mixing iron rust with the ratios of 0, 2.5, and 5 %) were applied with the recommendation level (1.5 Mg ha) before rice transplanting. Seasonal CH flux was significantly decreased by the original silicate fertilizer (BFS) application to 20 % over control. This effectiveness was enhanced by adding 2.5 % iron rust but thereafter, not more increased. Silicate fertilization (BFS) significantly increased rice grain productivity by 9 % over control, and the improved silicate fertilizer (BFS) more highly increased by 13 %. In conclusion, the BFS's functionality to increase rice productivity and suppress CH emission could be improved by adding an effective electron acceptor such as FeO.