"Recent analysis of 160 years of crop samples from Rothamsted Research Station near London discovered that levels of essential micronutrients remained consistent in wheat grain from 1844 to the late 1960s, but then began a decline that continues to this day.
The nutrient decline began when traditional long-straw wheat varieties where phased out in favour of higher-yielding semi-dwarf varieties.
As wheat plants have grown smaller since the 1960s, grain nutrient density has continued to decrease." (Thanks D)
Note that Zn is chronically deficient in our dryland calcareous soils.