Copper release from chemical root-control baskets in hardwood tree production

The City of Montreal, Canada, evaluated the environmental impact and usefulness of in-ground copper (Cu)-treated baskets in controlling root growth of hardwood trees in nursery culture. Using baskets planted with 5-yr-old Norway maple (Acer platanoides L.) trees, the amount and temporal pattern of Cu release from the basket surface into soil was determined for two copper formulations: Cu metal powder and Cu(OH)2. Release of both Cu formulations from the basket surface decreased exponentially over time, with Cu concentration at the basket surface dropping to 2% of the initial Cu applied by the end of the second field season. Total Cu content increased significantly in the soil around the baskets (from 7 to 28 mg Cu kg(-1) soil) and in the baskets (from 7 to 50-70 mg Cu kg(-1) soil) over the two years of the study. Three levels of phosphorus application (33, 66, and 100% of the regular nursery rate of 465 kg ha(-1) yr(-1)) did not affect release of Cu from the basket surface. The release of Cu metal at 28 and 105 d in the field was significantly increased by inoculation with the symbiotic arbuscular mycorrhizal fungus (AMF) Glomus intraradices Schenck & Smith; however, AMF inoculation had no affect on Cu(OH)2 release. Trees grown in Cu-treated baskets and inoculated with G. intraradices had similar colonization to non-inoculated trees, suggesting that inoculation was not very effective and that AMF inoculum was already present in the root ball of the trees at planting. After two years, copper basket-grown trees had significantly less root colonization than isolated control trees growing in the open field. This strongly suggests that conditions inside the baskets were not favorable to AMF.