Crops grown is western Canada will require anywhere from 1 - 4.5 g of Zinc/Bushel. Out of 724 Megalab soil samples taken in western Canada between 2010-2016, 24% of those were deficient in Zinc. The number rose to 32% deficient from tissue tests done in the same years.
A variable mobile nutrient within the plant, the availability of zinc in the soil can be reduced both by increasing soil pH and increasing phosphate levels within the soil. Subsequently calcareous soils, limed soils and soils receiving phosphate applications can bring about zinc deficiencies within the crop, even where zinc levels in the soil are sufficient.
Another factor effecting zinc availability in the soil is the level of organic matter. Zinc uptake from the soil requires the presence of natural chelating agents exuded by the plant roots or from decomposing organic matter. Soils low in organic matter can therefore also reduce availability and induce deficiencies.
Because of the variable mobility of zinc within the plant, symptoms can appear in old as well as new leaver, changing from a healthy green to a muddy grey-green usually in the center of the leaf. Spots of dead tissue appear and grow out of the leaf margins and the margins become crinkled.
In severe deficiency situations, the leaves have an oily appearance with the dead patches surrounded by yellow-green areas and the leaves tend to be small. The combined result of these symptoms is a loss of final yield at harvest.
The first priority with any crop is good root development (establishment). What grows above the ground is a reflection of how well the root system below the ground is developed. Early on it is vital to look at nutrients which influence root development, including zinc.
In the natural world of a seed, energy and nutrition for early establishment is provided by the nutrient reserves in the seed up to the point at which lateral roots develop an the young plant can "hunt" for its nutrients from the soil environment.
Seed reserves will vary, as will the soil into which the seeds are planted. It is therefore important to ensure the seed has access to adequate resources of zinc during the early growth stages to give the crop the best possible start.
Zinc can be applied on the seed, with or on the fertilizer (YaraVita PROCOTE) or on the leaf (YaraVita GLYTREL ZnP). For foliar application, once there is sufficient leaf cover to intercept a foliar spray (2 leaf stage onwards) applications should be made as early as possible, up to the point of first node detectable (Zadok's G.S 31). Applications later than this will produce diminishing returns due to the fact that zinc is primarily required for vegetative growth and flowering. The majority of the final yield potential is determined before the onset of stem extension and so it is vital to get the zinc into the crop well in advance of this to maximize this yield potential.
In interview to Real Ag Radio on March 28, 2019, Yara's Crop Manager Markus Braaten talks about the critical role each micronutrient plays in producing the best possible crop.