Soil and biological responses of wheat cropping system to Linz-Donawitz steel slag applied at different particle sizes and rates

Abstract

Steel slag, a by-product of steel manufacturing, holds potential as a soil amendment owing to its rich content of calcium, magnesium, iron, silica, and micronutrients, but its use raises concerns over heavy metal contamination and soil health. A controlled pot experiment was conducted during 2020-2022 at ICAR-Indian Agricultural Research Institute, New Delhi, to evaluate the effects of Linz-Donawitz steel slag of two particle sizes (<50 µm and 50-100 µm) and three application rates (0.25, 0.50, and 1.0 t ha-¹) on soil properties, heavy metal dynamics, microbial activity, and wheat performance. Results indicated that slag application had a marginal but positive role in reducing soil availability of Pb and Ni, particularly under finer particles at moderate doses, while Cd availability showed a slight increase though within safe limits. Chromium availability remained unaffected across treatments. Soil biological attributes responded variably: phosphatase activities and microbial counts were significantly enhanced, especially under coarser particles and moderate slag rates, whereas dehydrogenase activity and microbial biomass carbon declined at higher doses, suggesting microbial stress under elevated alkalinity and Ca²⁺ levels. Overall, moderate applications of slag improved enzymatic activity and microbial abundance without exceeding heavy metal safety thresholds, while excessive inputs showed diminishing or adverse effects. The study demonstrates that steel slag, when applied judiciously, can serve as a low-cost, eco-friendly soil amendment in wheat systems by improving nutrient cycling and reducing certain heavy metal availabilities. However, long-term field evaluations are essential to validate sustainability, optimize application strategies, and minimize environmental risks.