Wheat (Triticum aestivum) response to micronutrients (Mn, Cu, Zn, B) in Canterbury, New Zealand

Trials were carried Out at 20 sites in 2004-05 and at three sites in 2000-07 to determine if micronutrient application is required to maximise wheat yields in Canterbury, New Zealand. Micronutrients were applied at recommended rates as solid fertiliser (zinc (Zn) and boron (B)), foliar spray (manganese (Mn)), or both (copper (Cu)). Foliar treatments increased Cu and Mn in vegetative tissue, but not in grain. Soil-applied CuSO4 had little or no effect oil plant Cu. Sodium borate (2.3 kg B/ha) increased plant B by an average of 68% at mid-late tillering (Zadoks growth stage 22-29). Zn (4.4 kg/ha as ZnSO4) gave small improvements in plant Zn (generally <20%). In 2004-05, there was no yield response to the treatments, even though about half the sites were below the suggested critical soil thresholds for Cu and Zn. In 2006-07, two sites showed yield responses (LIP to 0.9 t/ha) to Mn, but not to Zn or Cu. The soil EDTA (ethylenediaminetetraacetic acid) test was generally a poor indicator of wheat micronutrient status. The critical tissue Mn concentration to achieve 95% of maximum yield was estimated at 13 mg/kg at car emergence. Our results suggest that wheat crops with >= 12 mg Zn/kg at mid-late tillering or >10 mg Zn/kg at ear emergence do not respond to applied Zn. Crops with >= 2 mg Cu/kg at mid-late tillering were not responsive to Cu.