Assessment of metal(loid)s phytoavailability in intensive agricultural soils by the application of single extractions to rhizosphere soil

• CEC, OM, oxides and clay significantly influence metal(loid)s phytoavailability.
• Four soil extraction methods (Mehlich 3, DTPA, NH4NO3 and CaCl2) were tested.
• NH4NO3 is the most suitable soil extraction method for soil-plant studies.
• Rhizosphere soil should be used to accurately estimate metal(loid)s phytoavailability.
• A reliable prediction model of metal(loid)s content in lettuce shoot was obtained.

The influence of soil properties on the phytoavailability of metal(loid)s in a soil–plant system was evaluated. The content of extractable metal(loid)s obtained by using different extraction methods was also compared. To perform this study, a test plant (Lactuca sativa) and rhizosphere soil were sampled at 5 different time points (2, 4, 6, 8 and 10 weeks of plant growth). Four extraction methods (Mehlich 3, DTPA, NH4NO3 and CaCl2) were used. Significant positive correlations between the soil extractable content and lettuce shoot content were obtained for several metal(loid)s. The extraction with NH4NO3 showed the higher number of strong positive correlations indicating the suitability of this method to estimate metal(loid)s phytoavailability. The soil CEC, OM, pH, texture and oxides content significantly influenced the distribution of metal(loid)s between the phytoavailable and non-phytoavailable fractions. A reliable prediction model for Cr, V, Ni, As, Pb, Co, Cd, and Sb phytoavailability was obtained considering the amount of metal(loid) extracted by the NH4NO3 method and the main soil properties. This work shows that the analysis of rhizosphere soil by single extractions methods is a reliable approach to estimate metal(loid)s phytoavailability.

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