Upper critical level of copper to alfalfa, in ten Chilean soils

A pot-experiment to determine the Cu upper critical level (UCL) in some representative Chilean soils using alfalfa plants as indicators was carried out at La Platina Experimental Station from 1988 to 1989. Those soils having an abundant clay fraction dominated by 2:1 minerals and/or high organic matter contents retained Cu very strongly showing low Cu toxicity and high Cu-UCL. Reversely, those soils having few clay minerals or abundant ones dominated by 1:1 minerals and/or low organic matter contents showed weak Cu retention giving pronounced toxic effects reflected by low Cu-UCL values. Growth depletion was related to increased Cu content in the aerial biomass reflecting an additional Cu uptake by roots and its translocation into the aerial part of the plants; normal plants were associated to normal Cu contents in tissues.