Effects of steel slag applications on CH₄, N₂O and the yields of Indonesian rice fields: a case study during two consecutive rice-growing seasons at two sites

<div><p></p><p>The increasing human population requires greater rice production. However, rice cultivation contributes to global warming through greenhouse gas (GHG) emissions. Technologies for reducing GHG emissions in concert with the increased rice production from rice fields are needed. The objectives of this study were to evaluate the effects of steel slag applications on methane (CH₄) and nitrous oxide (N₂O) emissions and rice yields. Two study sites were established at the experimental farm belonging to Indonesian Agricultural Environment Research Institute (IAERI) in Jakenan and a farmer’s field in Wedarijaksa sub-district, Indonesia. Both field trials were conducted during the dry season (DS) of 2009 and the rainy season (RS) of 2009/2010. During the DS, a randomized block design was arranged with two treatments (a control and a steel slag application at 1 Mg ha⁻¹), which were replicated five times. During the RS, the experimental plot with 1 Mg ha⁻¹ of steel slag treatment was split into two small sub-plots to accommodate the additional 1 and 2 Mg ha⁻¹ steel slag treatments. The results showed that there was a decreasing tendency in the CH₄ emissions at both sites and during both seasons after steel slag applications, although there was no statistical significance. During the RS in Jakenan, steel slag applications at rates of 1 and 2 Mg ha⁻¹ decreased the CH₄ emissions by 9.1 and 10.7%, respectively. In Wedarijaksa, steel slag applications at rates of 1 and 2 Mg ha⁻¹ decreased the CH₄ emissions by 12.6 to 18.7%, respectively. The N₂O emissions were decreased by 34 and 38% following slag applications at the 2 Mg ha⁻¹ rate during the RS in Jakenan and Wedarijaksa, respectively. The iron content of steel slag could be used to reduce not only CH₄ but also N₂O emissions. Increased level of electron acceptors suppresses CH₄ and N₂O emissions. The application of steel slag at 1 and 2 Mg ha⁻¹ increased rice grain yields by approximately 4.8–5.6% in Jakenan and 0.3–4.7% in Wedarijaksa. It might be better to apply steel slag at higher rates for more than two growing seasons to reach reduction in CH₄ and N₂O emissions.</p>