The residual effectiveness of previously applied copper fertiliser for grain yield of wheat grown on soils of south-west Australia

Abstract

The residual effectiveness of copper (Cu) applied 18 to 21 years previously was estimated for grain yield of wheat. In one field experiment, current levels of Cu fertiliser were applied and its effectiveness was compared to that of the same level of Cu applied previously. The effects of nitrogen (N) fertiliser on the Cu concentration in the youngest emerged blade and in the grain, as well as the effects of N levels on the grain yield of wheat, were also studied.

Where the recommended level of Cu fertiliser had been applied previously, its residual effectiveness depended on the soil type. On the grey sands over clay and gravelly sands over clay, the residual Cu would last approximately 20 years where wheat is grown in rotation with a legume crop (Lupinus augustifolius L.) and where N fertiliser is applied at high levels (92 kg N ha⁻¹). On the yellow brown sandy earths of the Newdegate district, the residual value was in excess of 30 years.

When Cu levels in the soil are marginal, high levels of N applied to wheat crops grown on stubbles of legume crops (high soil N) could suffer from induce Cu deficiency which could reduce grain production.

Critical concentrations of Cu in the youngest emerged blade of less than 1.2 mg Cu kg⁻¹ at Gs50–59 would indicate Cu deficiency. Cu concentrations of less than 1.1–1.2 mg Cu kg⁻¹ in the grain suggest that the wheat crop is marginally supplied with Cu. In both situations, Cu fertiliser needs to be applied before the next crop.