Micronutrient availability from steel slag amendment in peatmoss substrates

Authors: Altland, James; Zellner, Wendy; Locke, James; Krause, Charles

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/9/2015
Publication Date: 11/1/2015
Publication URL: http://handle.nal.usda.gov/10113/61861
Citation: Altland, J.E., Zellner, W.L., Locke, J.C., Krause, C.R. 2015. Micronutrient availability from steel slag amendment in peatmoss substrates. HortScience. 50:1715-1720.

Interpretive Summary: Steel slag is a byproduct of the steel industry, recently introduced as a liming agent for agricultural purposes and has potential for use in greenhouse substrates. As steel scraps and iron ore are melted in a basic oxygen furnace (BOF), calcium oxide (CaO) and dolomitic lime are introduced as fluxing agents to remove impurities from the molten steel. Mineral impurities removed by the fluxing agents, along with the calcium oxide and dolomitic lime, form a molten slag. The slag is poured off from the steel, cooled, and processed into particle size fractions ranging from dust to gravel. The impurities removed from the molten steel by the fluxing agent include varying concentrations of elements considered to be plant micronutrients. The objective of this research was to determine if the steel slag could provide all the required micronutrients needed for growing floriculture crops in a peatmoss substrate. Geranium and tomato plants were grown in substrates amended with varying rates of steel slag. Compared to other plants which were fertilized with traditional micronutrient sources, those grown with the steel slag amendment were smaller and displayed symptoms of nutrient deficiency. In geranium, foliar nutrient concentrations suggest Cu and Zn were limiting due to the concentrations found in steel slag-amended crops relative to the control plants. In tomato plants, foliar nutrient concentrations suggest B and Zn were limiting. Based on the results of this research, steel slag does not provide sufficient micronutrients, most notably B, Cu, and Zn, to be the sole source of micronutrient fertilization for floriculture crops grown in peatmoss substrates.

Technical Abstract: The objective of this research was to determine the suitability of a steel slag product for supplying micronutrients to container-grown floriculture crops. Geranium (Pelargonium xhortorum 'Maverick Red') and tomato (Solanum lycopersicon 'Megabite') were grown in 11.4 cm containers with a substrate composed of 85 peatmoss : 15 perlite (v:v). A group of containers referred to as the commercial control (C-control) were amended with 4.8 kg.m-3 dolomitic lime and fertilized with a commercial complete fertilizer providing macro and micronutrients (Jack’s 20N-4.4P-16.6K-0.15Mg-0.02B-0.01Cu-0.1Fe-0.05Mn-0.01Mo-0.05Zn, JR Peters, Inc., Allentown, PA) at a rate of 100 mg.L-1 nitrogen (N). Another group of containers, referred to as the micronutrient control (M-control), were amended with a commercial granular micronutrient package at 0.9 kg.m-3 and dolomitic lime at 4.8 kg.m-3. The M-control group was fertilized with 3.6 mM N (100 mg.L-1 N) with ammonium nitrate and 2 mM potassium phosphate. A final group of containers were amended with 1.2, 2.4, or 4.8 kg.m-3 of steel slag and fertilized with 3.6 mM ammonium nitrate and 2 mM potassium phosphate. Both control groups resulted in vigorous and saleable plants by the conclusion of the experiment. In both crops, chlorophyll levels, root ratings, and shoot dry mass were lower in all steel slag-amended plants compared to either control group. In geranium, foliar nutrient concentrations suggest Cu and Zn were limiting while B and Zn were limiting in tomato. Based on the results of this research, steel slag does not provide sufficient micronutrients, most notably B, Cu, and Zn, to be the sole source of micronutrient fertilization in container-grown crops.