Copper nutrition of subterranean clover (Trifolium subterraneum L. cv. Seaton Park). II. Effects of copper supply on distribution of copper and the diagnosis of copper deficiency by plant analysis

Abstract

The effect of copper supply upon the distribution of copper within Seaton Park subterranean clover was examined from early vegetative growth to plant maturity in one glasshouse experiment, and in a second experiment was assessed at early flowering. The copper content of old leaf blades of copper-adequate plants decreased progressively with senescence of the blades. Copper deficiency delayed senescence and export of copper from the older blades so that both the relative and net changes were substantially smaller than for blades of copper-adequate plants. However, copper concentrations in senesced old leaf blades still reflected copper supply. At full senescence these blades contained appreciable quantities and concentrations of copper which contrasted with the low levels found in senesced leaves of wheat and peanuts in previous studies. Copper concentration in whole plant tops was not satisfactory for diagnosing copper deficiency, since the critical concentration decreased with plant age and during late vegetative development 'Piper-Steenbjerg' curvature developed in the relationship between copper concentration and yield. It is possible that the curvature resulted partly from unusually high concentrations of copper in the old petioles of severely deficient plants. Analysis of copper in young leaf blades provided a sensitive means of diagnosing copper deficiency in subterranean clover. The estimated critical concentration for these blades (3 ¦g/g for maximum growth) did not change with plant age, at least until early flowering. In early growth, the copper concentration of young leaf blades may be used to forecast impending copper deficiency.