The effect of copper supply on vegetative and seed yield of pasture legumes and the field calibration of a tissue test for detecting copper deficiency. I. Subterranean clover (Trifolium subterraneum and Trifolium yanninicum)

Abstract

Three cultivars of subterranean clover (Trifolium subterraneum L. cvv. Woogenellup, Nungarin; Trifolium yanninicum cv. Trikkala) were grown on three copper-deficient soil types at seven rates of copper, applied at sowing, to determine their vegetative and seed yield response to copper fertilizer.On two soil types, symptoms of copper deficiency were apparent where no copper was supplied. On the third, symptoms appeared only in one season, after the site was waterlogged. On the three soil types, the symptoms disappeared when 0.125 kg Cu/ha was applied at sowing. although at this rate vegetative and seed yields were reduced by as much as 44% and 59% respectively.The proposed critical concentration range in youngest open leaf tissue for both diagnosing maximum vegetative dry matter and predicting maximum seed yield is 3.0-4.5 mg Cu/kg for Woogenellup and Nungarin subterranean clover. Trikkala subterranean clover had higher critical concentration ranges for diagnosing maximum vegetative dry matter (4.0-6.0 mg Culkg) and predicting maximum seed yield (4.5-7.0 mg Cu/kg). It was not clear whether this difference was due to a higher internal requirement for copper of Trikkala or overlying environmental conditions affecting the external copper supply at the time of sampling.For whole top tissue (WT), there was no difference in the critical concentration range between the three cultivars for diagnosing maximum vegetative yield (3.0-4.0 mg Cu/kg). However, the critical concentration in WT for predicting maximum seed yield was higher for Trikkala (5.0-6.0 mg Cu/kg) than Woogenellup and Nungarin (3.5-4.5 mg Cu/kg). In the pasture situation, a critical concentration of 5.0-6.0 mg Cu/kg in the WT should be adopted when animal requirement is considered.Seed copper concentration for predicting maximum seed or vegetative yield was not a reliable indicator of copper status of subterranean clover.