Effect of nitrogen on the availability of previous and current applications of copper fertiliser for grain yield of wheat grown in south-west Western Australia

Abstract

Twenty-one field experiments located in different rainfall zones on a range of soils that had been fertilised with copper (Cu) fertiliser 16-23 years previously were used to examine the effect of level of nitrogen (N) fertiliser on the grain yield of wheat. At 1 site (experiment 15), no Cu fertiliser had been applied. The effect of applied N on Cu concentrations in the youngest emerged blade (YEB) and in the grain was also studied. At 20 sites, there was no further response to currently applied Cu fertiliser. The highest level of N fertiliser applied (46-92 kg N/ha) did not induce Cu deficiency in wheat plants. The addition of Cu increased Cu concentration in the YEB and grain, whilst increasing the rate of N fertiliser generally decreased these concentrations of Cu. At 2 sites in the Jerramungup district, the addition of N induced Cu deficiency in wheat, which reduced grain yields. Increasing the rate of N fertiliser reduced Cu concentration in the YEB to deficient levels (< 1.0 mg Cu/kg); Cu concentrations in grain were <0.8 mg/kg. Only 50% of the recommended Cu fertiliser had been applied in previous years at 1 site (experiment 12). At the other site, Cu appears not to have been previously applied, because the ammonium oxalate soil-extractable Cu measured in soil samples collected from the site and adjacent uncleared soil were identical and very low (0.25 mg Cu/kg). At 1 high-yielding site (>3.0 t/ha), the highest level of N (92 kg/ha) reduced Cu concentration to 1.0 mgkg in the YEB and 1.0 mg/kg in the grain without reducing grain yield. It is concluded that high levels of N fertiliser application did not increase the wheat plants' requirement for Cu fertiliser where Cu fertilisers had been applied at the recommended level in the past 23 years. Where Cu fertiliser has been applied at lower-than- recommended levels in previous years, Cu deficiency occurred where high levels of N were applied.