Copper Deficiency in Cereal and Oilseed Crops in Northern Canadian Prairie Soils 1

Transitional grassland/forest light soils in Saskatchewan are often deficient in Cu. The high cost of micronutrient fertilizers necessitates extreme care in identifying micronutrient deficiencies and selecting effective products and methods of application. Comparison of tissue and grain or seed analysis for spring wheat ( Triticum aestivum L.), canola ( Brassica napus L.), and flax ( Linum usitatissimum L.) vs. DTPA‐extractable soil Cu levels revealed that diagnosis of Cu deficiencies can more accurately be achieved via the latter. The critical DTPA‐extractable Cu levels were 0.40 mg Cu kg −1 of soil for spring wheat and 0.35 mg Cu kg −1 of soil for canola and flax. A series of field experiments comparing different forms of soil and foliar Cu fertilizers were conducted on several transitional grassland/forest soils. Copper oxide applied in the spring was generally ineffective in the year of application but alleviated Cu deficiencies in the following year. Copper‐sulfate (blue stone) and chelated products (polylignosulphonic acid) were effective in the year of application. However, the latter had no residual value at the rates of application used. This, combined with their extremely high current prices, makes them an undesirable Cu fertilizer source for the soils in the study area. Foliar Cu applications of either Cu‐sulfate or Cu‐chelate may be effective, but their performance has been erratic; hence, they should only be considered as an emergency measure for correcting of Cu deficiency.