Selecting a nitrogen availability index for understanding plant nutrient dynamics in rehabilitated bauxite-processing residue sand
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Understanding nutrient dynamics in non-typical soil materials such as bauxite-processing residue sand(pH > 10; EC > 30 dS m-1) is critical for developing fertilizer strategies and evaluating ecological restorationperformance. Indices relating nitrogen (N) concentration in soil to plant N uptake are well-established fornatural soils but their application to non-typical soils has received little attention. This study investigateda range of soil-based methods [i.e. 2 M KCl extractable inorganic N (NH4+, NO3-), potentially mineralizablenitrogen (PMN), and 0.01 M CaCl2extractable N] to identify their suitability for describing soil-plant Nrelations in highly alkaline bauxite-processing residue sand. Nitrogen availability indices were measuredunder laboratory (pot trial) and field conditions. Pot trial was established using residue sand that had beenamended (10%, v/v, basis) with various organic (greenwaste compost, biochar and biosolids) and inorganic(zeolite) materials. Both the field study and pot trial showed that 2 M KCl extractable NO3--N was mosthighly correlated with plant biomass N compared with the other N availability indices. Findings fromthis study suggest that 2 M KCl extractable NO3--N can be used as a soil quality indicator in developingfertilizer management strategies and assessing ecological status of the residue storage areas.