Corn yield the past 5-6 years has been mostly influenced by how much excess rain we accumulated.  Then 2020 happened and hot, dry conditions reminded us that during stress soil fertility is number 1 in yield performance and handling stress.  You have to feed the plants and if the soil test indicates only 32,000 plants can be feed in a particular field, you better plant 32,000.
Also, the attached photo of 4 different hybrids planted in a stressed environment in northern Iowa, indicate the imprortance of genetically based root size in a hot, dry weather pattern.  When a plant is trying to scavage limited moisture and fertility, the size of the root matters.  And root size is determined by the male and female inbreds use in creating a particular hybrid.
Those who pay attention to these 2 agronomic items will be better next year if the pattern of hot, and dry persists.  It was amazing to me the consistency of rainfall from 2014 through 2019.  It would not surprise me to see a hotter, dryer pattern in the next few years.