EXTRACTANTS FOR ASSESSING THE AVAILABILITY OF COPPER TO CHRYSANTHEMUM-MORIFOLIUM CULTIVAR YELLOW MANDALAY GROWING IN SOILLESS MEDIA

Concentrations of copper (Cu) in saturation extracts containing diethylenetriamine-N,N,N',N'',N''-pentaacetic acid (DTPA), and in 2 mM DTPA (1:1.5 by volume) extracts, increased linearly with additions of Cu (as CuSo4·5H2O) to peat, Pinus radiata bark and composted sawdust. It look ∼4 days for extractable Cu levels to stabilize after Cu had been added to the substrates. Chrysanthemum morifolium cultivar 'Yellow Mandalay' had chlorotic leaves and reduced vegetative growth, when grown in media comprised mainly of composted Eucalyptus marginata sawdust, if saturation extracts containing DTPA and 2 mM DTPA (1:1.5 by volume) extracts of the media contained less than ∼1 and 0.25 mg l-1 Cu, respectively. However, under the conditions of this experiment, maximum reproductive growth was possible only if the extracts contained at least ∼ 11.7 and 5.1 mg l-1 Cu, respectively. The results suggest that additions of Cu to soil-less media to be used for growing flowering plants should be higher than when only vegetative growth is needed, and should be in the range 10-20 mg l-1. Critical Cu concentrations in bulked leaves associated with optimum vegetative and reproductive growth were 2.4 and 10.3 mg kg-1, respectively. © 1990.