Slag from steel production as a versatile fertilizer: Evaluation of ladle furnace slag in sandy soils and hydroponics

Circular use of nutrients is a key endeavor towards a sustainable intensification of agriculture, which reduces emissions and prevents food scarcity. An under-applied source of key micronutrients is slag from steel production; although it has been explored for its potential use in agriculture, the multi-faceted benefits across crop types have not yet been realized at scale. Herein, ladle furnace slag is explored as an amendment for three plant types: cherry tomato, typically grown in acidic soils; Salicornia, typically grown in alkali and saline soils; and arugula, known for its hydroponic growth potential. Both sandy soils and hydroponics are considered. First, the controlled release of nutrients from slag and its fragmentation are shown to be highly associated with organic acids, linked to soil acidification from plant exudates. Low concentrations of slag are shown to increase plant root length and dry weight. For cherry tomatoes, when slag concentration increased from 0 % to 0.1 % slag (w/w), lateral root number, and tap root length increased by 88 % and 44 %, respectively. Similar effects were observed when arugula was hydroponically grown. The starkest contrast was observed for Salicornia, where slag addition increased the net weight by three-fold in the seedling stage. Overall, the study showed that emerging interactions between steel-making and agricultural industries could result in more efficient cropping, nutrient cycling, and carbon bio-fixation.