Effect of compost and biodegradable chelate addition on phytoextraction of copper by Oenothera picensis grown in Cu-contaminated acid soils

Oenothera picensis plants (Fragrant Evening Primrose) grow in the acid soils contaminated by Cu smelting in the coastal region of central Chile. We evaluated the effects of compost, at application rate of 5 kg m−2, and biodegradable chelate MGDA (methylglycinediacetic acid), at application rate of 6 mmol plant−1, on Cu phytoextraction by O. picensis, in field plots. No significant differences were found between treatments regarding aboveground biomass, shoot Cu concentrations and Cu phytoextraction of O. picensis. This lack of effects of the treatments was provoked by the large variability of soil properties, prior to applying of the treatments. The shoot Cu concentration in O. picensis positively and significantly correlated to exchangeable Cu concentration in the soil. Likewise, the aboveground biomass of O. picensis positively and significantly correlated to soil organic matter content. The Cu phytoextraction by O. picensis, in turn, positively and significantly correlated to both variables, i.e. exchangeable Cu concentration and organic matter content. The average Cu phytoextraction was 1.1 mg plant−1, which is equivalent to 90 g ha−1 at planting rate of 8 plants m−2. In the chelate treatment, Cu phytoextraction was 2.6 ± 2.1 mg plant−1, which is equivalent to 212 ± 171 g ha−1 at planting rate of 8 plants m−2.