Influences of soil properties and leaching on copper toxicity to barley root elongation

The relationships developed between soil properties and phytotoxicity threshold values for copper require validation in a wide range of soils with different properties and climate characteristics before they can be applied for regulatory purposes in countries throughout the world. Seventeen soils, which are representative of the major soil types and properties in China, were spiked with Cu chloride. A subset of the Cu-spiked soils was leached with artificial rain water to compare toxicity with that in unleached soils. Barley root elongation tests were performed under controlled environmental conditions. The concentrations of added Cu causing a 50% inhibitory effect (EC50) ranged from 67 to 1,129 mg/kg in unleached soils and from 88 to 1,255 mg/kg in leached soil. Compared with the unleached toxicity thresholds, the leached EC10 (10% inhibition) and EC50 were higher by an average of 1.43- and 1.15-fold, respectively. Soil leaching significantly (p <or= 0.05) decreased the toxicity of Cu in approximately 35% of the soils. In this study, no single soil property was found to explain over 35% of the variance in (log transformed) EC50. However, stepwise multiple regressions using soil pH, organic carbon (OC) content, and effective cation exchange capacity (eCEC) were found to explain over 80% of the variance in Cu toxicity across soils. The model developed for Chinese soils based on these factors was found to predict significantly (r(2), 0.90) the phytotoxicity of Cu in European soils. These quantitative relationships between Cu toxicity and soil properties are helpful for developing soil-specific guidance on Cu toxicity thresholds.

Bo Li, Yibing Ma, Mike J. McLaughlin, Jason K. Kirby, Gill Cozens and Jifang Liu