Evaluation of field application effect of a locally produced blast furnace slag for mitigating methane emission and improving rice productivity in Indonesian paddies

Indonesian paddy soils are generally characterized by strong acidity and low fertility, resulting in limited rice productivity and necessitating the continuous application of alkaline soil amendments. Although high-quality blast furnace slag (BFS), a byproduct of the steel industry rich in calcium (Ca), silicon (Si), and trace elements, is produced domestically in Indonesia, its potential as a soil amendment or fertilizer has not yet been fully utilized. Notably, BFS contains substantial amounts of oxidized iron (Fe), which can act as an electron acceptor, thereby helping suppress methane (CH₄) emissions during flooded rice cultivation. In this field study, rice cultivation experiments were conducted over four consecutive growing seasons in the lowland plains of Central Java (igneous rock–derived soils) and West Java (volcanic rock–derived soils) to evaluate the effects of Indonesian BFS on rice productivity and CH₄ emissions. BFS was applied at rates of 0, 1, 2, and 4 Mg ha⁻¹ prior to transplanting in each season. CH₄ emissions were characterized during cropping seasons, and rice yield and soil chemical properties were analyzed at harvest. At both sites, CH₄ emissions decreased significantly with increasing BFS application rates, with an average reduction of 8% per Mg ha⁻¹ of BFS. Rice grain yield exhibited a concave quadratic response to BFS application, estimating a maximum grain yield at approximately 2.5 Mg ha⁻¹, which corresponded to an average increase of 17% compared to the control. In addition, the BFS application improved key soil chemical properties, indicating enhanced soil quality. Overall, Indonesian BFS effectively improved soil conditions, increased rice productivity, and mitigated CH₄ emissions. These findings highlight the strong potential of locally produced BFS as a sustainable soil amendment for climate-resilient rice production systems in Indonesia.