Quantifying the relative contribution of driving factors to the transformation of bauxite residue into a plant growth substrate

The vast stock and increasing amount of bauxite residue with high alkalinity, low nutrient and poor structure poses a significant challenge to plant growth. Although additives have been recognized to have obvious effects on the transformation of bauxite residue to a soil-like media for plant growth, a clear understanding of the quantitative contribution of physicochemical properties to plant growth is missing. This study aimed to discuss the portrayed role and contributions of additives mediated alkalinity, nutrient, and aggregates component in the significant factors of aggregate structure formation and corresponding plants seed germination in bauxite residue. The regulation of pH and total alkalinity in bauxite residue depends on inorganic additives, while for ESP and nutrients, nitrohumic acid and vinegar residue are better than inorganic and citric acid. The silt-clay fraction and microaggregate increased from 35.1% and 25.6% to 40.8% and 31.9% within citric acid addition, respectively, while macroaggregate increased from 39.2% to 49.9% within nitrohumic acid application, indicating citric acid may be more involved in the formation of the fundamental building units of organo-mineral associations in bauxite residue, while nitrohumic acid and vinegar residue may play an important role in continuous aggregation of small particles. For aggregates component, calcium in silt-clay fraction had the largest explanatory power in aggregate stability and germination rate (R 2 = 65.6%), followed by Al in 0.25–2 mm size fraction (R 2 = 11.1%), while organic complex Fe oxides and Mg in microaggregate explained little variance (R 2 = 3.89% and R 2 = 1.25%), demonstrating Ca, Fe, and Mg contributed greatly to the formation of microaggregate, while Si and Al contributed greatly to the formation of large aggregate. Besides the dominant role of aggregates component, aggregate stability related to mean weight diameter, large macroaggregates, fractal dimension, and silt-clay fraction plays a more critical role in seed germination. • Regulation of pH and TA in bauxite residue mainly depends on inorganic additives. • Organic additives facilitated ESP reduction and aggregate structure improvement. • Citric acid promoted the organo-mineral associations formation in bauxite residue. • Nitrohumic acid and vinegar residue were important in small particles aggregation. • Structural improvement assists plant germination more than alkalinity and nutrient.