The importance of micronutrients, including boron (B), chloride (Cl), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), zinc (Zn) and nickel (Ni), has come under the microscope in recent years. Some researchers say a lack of micronutrients can cause yield loss.
According to Tee Boon Goh, a specialist in soil chemistry and mineralogy at the University of Manitoba, and Rigas Karamanos, a senior agronomist with Koch Fertilizer Canada, ULC, copper is an essential element for wheat growth. Goh and Karamanos are the co-authors of a pamphlet entitled “Does addition of copper increase the macronutrient content of wheat?” recently presented to the Manitoba Agronomists’ Conference at the University of Manitoba in December 2014.
Goh and Karamanos identify copper as essential to wheat because it is involved in a number of plant functions, such as electron transfers, chlorophyll production, protein synthesis and respiration.
Copper deficiency can have severe impacts on wheat yields. “Copper deficiency in wheat produces characteristic symptoms of yellowing and curling of young leaves, pigtailing of leaf tips, limpness or wilting, delay in heading, aborted heads and spikelets, head and stem bending, as well as stem melanosis disease in certain wheat cultivars,” says Goh.
The researchers tested the hypothesis that copper can be applied in an effort to increase macronutrient uptake, and in particular nitrogen uptake, and subsequently high protein in the wheat seed. They took into account 47 experiments that had been conducted on a total of 2,648 separate plots, and examined the impact of copper on protein levels (where measured), or the macronutrient tissue content in each of these 47 previously conducted experiments.
Wheat is sensitive to copper
Goh and Karamanos chose copper as their focus because, while lack of any of the micronutrients will cause yield losses in wheat, the crop is particularly sensitive to copper and manganese, and there is a large volume of research conducted on copper. “It is estimated that there are close to five million acres of deficient or potentially copper deficiency soils in the Prairies,” says Karamanos.
The study, almost exclusively funded by Western Cooperative Fertilizers Ltd. (Westco), showed 18 significant yield responses and 21 non-significant yield responses to the addition of copper to the soil’s macronutrient content.
“Claims that application of copper (either foliar or soil applied) increase nutrient content and in particular protein content are unfounded,” Goh and Karamanos concluded in their report.
“Micronutrients are essential elements; however, unless there is a deficiency in any given micronutrient, they contribute little to improving nutrients that are required in higher quantities, such as nitrogen, phosphorus, potassium and sulphur,” says Karamanos. “As a matter of fact, when soils are deficient in copper, correction of the deficiency resulted in a decrease in macronutrient concentration and protein content, as a result of a simple dilution effect.”
This is not to say that the targeted application of copper is not important in deficient soils.
Goh says that a large body of research in Western Canada clearly shows that targeted application of micronutrients, including chloride, copper, zinc and manganese, based on valid soil test criteria, contributes to significant yield increases.
The key word is “targeted”: non-targeted applications of copper in wheat results in no benefit to the crop. Untargeted copper applications, says Goh, “are a waste of money on expensive material.”
According to Goh and Karamanos, the claim that copper can be applied to increase protein content in wheat is based on crops achieving “better health.” But they say “plant health” is a contested notion with many definitions.
“Although there are numerous studies on the general health definitions and health criteria in human medicine, plant health is not a well-defined and often misused term,” says Goh.
For consumers, Goh says, plant health may refer to crops free of pesticides and other chemicals with high nutritional value, whereas for regulators, it means crops free of heavy metals and toxins, for example. “For the producer, ‘plant health’ means crops achieving their full genetic potential, but even this varies depending on the type of crops. Plant health measures a wide spectrum of perceptions about the ‘fitness’ of a plant for varying objectives of groups of people and the debate is still on,” he says.
“This work addressed the impact of copper on other macronutrients from a plant nutrition perspective and in particular its effect on the nitrogen content, which is the main component of protein for which farmers are compensated,” says Karamanos of the study. “Any extrapolation to a loosely defined ‘plant health’ would be non-scientific at this point and only lead to confusion.”