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Research Project: Development of Technologies and Strategies for Sustainable Crop Production in Containerized and Protected Horticulture Systems

Location: Application Technology Research

Title: Micronutrient availability from steel slag amendment in pine bark substrates

Author
item Altland, James
item Locke, James
item Zellner, Wendy

Submitted to: Journal of Environmental Horticulture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/13/2016
Publication Date: 9/12/2016
Citation: Altland, J.E., Locke, J.C., Zellner, W.L. 2016. Micronutrient availability from steel slag amendment in pine bark substrates. Journal of Environmental Horticulture. 34(3)67-74.

Interpretive Summary: Steel slag is a byproduct of the steel industry. Similar to dolomitic lime (DL), it is white to gray in color, available in a range of particle sizes, and useful for raising substrate pH. A steel slag material has recently been made available for horticultural uses. In addition to its use as a liming agent, steel slags typically have measurable concentrations of micronutrients. The objective of this research was to determine if steel slag could be used as the sole micronutrient source for container-grown nursery crops. Butterfly bush (Buddleja davidii 'Pink Delight') and rose (Rosa 'Radrazz') were grown in #3 (3 gal) containers. A base substrate composed of 80 pine bark : 20 peatmoss was amended with either 1.2, 2.4, or 4.8 kg.m-3 of steel slag. Slag-amended substrates were compared with two control groups representing common industry methods for supplying micronutrients to container substrates. In one group, the base substrate was amended with a complete controlled release fertilizer (CRF) including micronutrients (C-control), and in the other the base substrate was amended with a different CRF containing only N, P, and K along with a granular micronutrient package (M-control). All plants appeared vigorous and green in color throughout the experiment, with no signs of nutrient deficiency or toxicity. However, plants grown in the substrate amended with the highest slag rate (4.8 kg.m-3) had less shoot growth than both control groups. Among the micronutrients analyzed, only Cu was consistently deficient in both the substrate and foliar tissue of slag-amended treatments. Steel slag either does not provide a sufficient quantity of Cu or the concomitant increase in pH with increasing rates of steel slag renders Cu unavailable for plant uptake. While steel slag is effective in raising substrate pH similar to dolomitic lime, it should not be used as the sole source of micronutrients for shrubs grown in pine bark based substrates.

Technical Abstract: Steel slag is a byproduct of the steel industry that can be used as a liming agent, but also has a high mineral nutrient content. While micronutrients are present in steel slag, it is not known if the mineral form of the micronutrients would render them available for plant uptake. The objective of this research was to determine if steel slag could be used as the sole micronutrient source for container-grown nursery crops. Butterfly bush (Buddleja davidii 'Pink Delight') and rose (Rosa 'Radrazz') were grown in #3 (3 gal) containers in a base substrate composed of 80 pine bark : 20 peatmoss. The base substrate was amended with the following treatments: with a complete controlled release fertilizer (CRF) including micronutrients (C-control), a substrate amended with a different CRF containing only N, P, and K along with a granular micronutrient package (M-control), and three additional treatments amended with the CRF (N, P, and K only) and either 1.2, 2.4, or 4.8 kg.m-3 of steel slag. Plants were harvested at 2 and 4 months after potting (MAP). None of the plants displayed any sign of nutrient deficiency or toxicity throughout the experiment. However, plants grown in the substrate amended with the highest slag rate (4.8 kg.m-3) had lower SDW than both control groups. Substrate pH increased with increasing slag rate, which may have affected micronutrient availability in those substrates. Among the micronutrients analyzed, only Cu was consistently deficient in both the substrate and foliar tissue of slag-amended treatments. Steel slag either does not provide a sufficient quantity of Cu or the concomitant increase in pH with increasing rates of steel slag renders Cu unavailable for plant uptake. Steel slag should not be used as the sole source of micronutrients for shrubs grown in pine bark based substrates.