LD Slag as a Soil Amendment and Nutrient Source in Sustainable Agriculture: A Review

The steel industry has grown rapidly, leading to the production of large quantities of steel slag, a by-product from processes like basic oxygen, electric arc, and ladle furnaces. Once seen as an industrial waste, steel slag is now valued in agriculture as a soil enhancer and nutrient source. This review aims to summarise key findings on how steel slag affects soil chemistry, nutrient dynamics, microbial interactions, and crop performance, while also addressing safety and practical considerations for its use in agriculture. This review highlights the benefits of using steel slag in sustainable farming, focusing on its nutrient content, environmental safety, and influence on crop productivity. It is rich in essential plant nutrients such as calcium, silicon, magnesium, and phosphorus, along with micronutrients like iron and manganese. Its alkaline nature helps to reduce soil acidity, improve nutrient availability, and support microbial activity in the soil. Steel slag is a by-product produced during steel manufacturing and is mainly generated from three types of furnaces: basic oxygen furnaces (BOF), electric arc furnaces (EAF), and induction furnaces (IF). Steel slag also has the ability to reduce the mobility of harmful metals like cadmium, arsenic, and lead, lowering the risk of heavy metal contamination in crops. Its application improves crop growth, enhances stress tolerance, and boosts yield. Steel slag with biochar in paddy fields raised soil pH by 14.2% and salinity by 98% compared to untreated soil. Field studies from Bangladesh, China, Japan, Indonesia, and Korea have shown that slag fertiliser can reduce methane emissions from rice fields by 0.6% to 56% depending on factors like soil type, slag composition, and application rate. Moreover, it helps to reduce methane and nitrous oxide emissions in flooded rice fields by altering soil microbial dynamics and redox conditions. When combined with materials like biochar, slag enhances carbon retention and microbial health, supporting long-term soil fertility. This review compiles recent research on various types of slag used in farming, emphasising their role in improving soil properties, limiting toxic metal uptake, and supporting sustainable crop production. It also addresses safety and regulatory considerations for practical use in agriculture. Research has shown that slag use can increase crop yields, improve plants’ resistance to stress and diseases, and make farming more sustainable. With proper management, steel slag can be a low-cost, eco-friendly option to improve soil quality and support sustainable agriculture.