Q: How do I know if I have copper-deficient soils?
A: Copper is the micronutrient most often found deficient in Western Canada.
In a nutshell, copper deficiency is most often found in deep sandy soils and peat soils, and wheat is the most sensitive crop. Soil tests are a good tool to predict potential copper deficiency. Crops yields are often reduced if soil copper is less than 0.4 to 0.6 parts per million. Copper plays a role in flower fertility, so yields may quickly decline if deficiency occurs.
There are several fertilizer products that can help alleviate copper deficiency. Remember: copper is a micronutrient — a good crop of wheat will remove less than 10 grams of copper per acre. The key is to apply enough copper in an available form so that it is available to the crop during the critical flowering period. Liquid copper at 0.1 to 0.2 pounds per acre applied to the foliage between the sixth and flag leaf of wheat has proven most effective for maximum annual yield response in truly deficient soils. In some cases, it may make sense to also try to build soil reserves of copper — this will require at least one to two pounds of actual copper applied each year. This is far more than crop removal, but high rates are needed to provide uniform distribution of the fertilizer granules, take into consideration low solubility of copper fertilizer and to account for adsorption of copper to the soil.
How do you decide if copper is required? Begin with a soil test of the soil landscape that you think will be most deficient. Then a field response trial with strips of foliar-applied copper on wheat (or other cereal crops) is the best way to confirm the size of crop response.
Lyle Cowell, P. Ag, CCA, is a manager of agronomic services with Nutrien Ag Solutions in northeast Saskatchewan.