Evaluation of six soil extractants for assessing nickel availability to wheat

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Abstract
The soil chemical processes affecting the availability of Ni uptake by plants are important in considerations of the impact of soil contamination on human health. The objectives of this study were to investigate the efficacy of six extraction solutions in removing Ni from twenty‐two calcareous soils and to evaluate these extractants as predictors of plant‐available Ni for wheat (Triticum asetivum L.) in the greenhouse. The soils received 0 and 125 mg Ni kg‐1 as NiC12 and are referred to as noncontaminated and contaminated soils, respectively. Of the six soil extractants, 1 M HNO3 was the most effective extradant for Ni from noncontaminated and contaminated soils. However. 0.1 M EDTA. 0.025 M Ca‐DTPA‐B4O7 and 0.005 M DTPA were equally‐effective in their ability to extract Ni from contaminated soils. The 0.025 M Ca‐DTPA‐B4O7 solution was the best in predicting Ni uptake by wheat in both noncontaminated [r = 0.95∗∗∗ (significant at p = 0.001)1 and contaminated (r = 0.91∗∗∗) soils. The relationships between the amounts of soil Ni extracted by the six procedures and plant uptake were improved when soil parameters (e.g., exchangeable cations. H2O soluble Na. organic matter) were included in multiple regression models. The results of this study show that the 0.025 M Ca‐DTPA‐B4O7procedure has a definite advantage over the other extraction procedures in the evaluation of the amount of plant‐available Ni in calcareous soils.