Copper deficiency has been recognised for some time in many areas, particularly in the Temora district od southern NSW. Yield responses to applications of Copper in wheat crops where deficiency has been identified have been well documented since the early 2000’s.
The critical soil test value for Copper is 0.3 mg/kg, below this deficiency symptoms are likely to occur. Ideally soil Copper levels should be 0.6 – 0.8 mg/kg. Care should be taken not to raise the Copper level too high, as Copper toxicity may result. An approximate rule of thumb is that applications of 2 kg/ha of Copper will raise the soil Copper level by 0.16 mg/kg.
The situation with Zinc is less clear. Direct responses to Zinc are often only visual, which do not always translate through to yield. Research also indicates that the presence of Zinc has been shown to decrease the incidence and severity of Rhizoctonia, however this has not been confirmed. Other factors that may be a more significant with Rhizoctonia incidence include – the green bridge, the use of Sulfonylurea herbicides, cultivation and seasonal conditions.
There has not been any demonstrated preference for either seed, foliar or fertiliser applied Zinc. For a long term benefit, through increased soil Zinc levels, a fertiliser treatment is preferred.
Copper (Cu) and Zinc (Zn) can be applied either as a seed treatment, fertiliser treatment, or foliar spray. Following are rates and costs of each option:
Activist Zinc (30% Zinc)– seed treatment
- Wheat application rate 4.0 L/tonne
- Applies 72 g/ha Zinc
- Cost $1.80/ha @ 60 kg/ha seed
- Canola application rate 20 L/tonne
- Applies 12 g/ha Zinc
- Cost $0.37/ha @ 2.5 kg/ha seed
- MAP + 1% Zn
- Applies 400 g/ha Zinc @ 40 kg/ha fertiliser
- Cost approximately $40/tonne or $1.60/ha @ 40 kg/ha MAP