Modern science has increased yield for corn by a factor of 8: https://images.app.goo.gl/QfcFrk4nvu7uw6M67. I’m only 35 and it’s doubled in my lifetime.
I bet that we could find good old forgotten varieties put in a vault for decades and then renamed, trademarketed, and rebranded as super new varieties much more productive for example. Only the best of the old varieties survived to out times. Much of the new super-varieties will not perdure when the layers of marketing will wear off.
There is an improvement of course, but not necessarily sustainable in time, or so high as expected.
[0] https://rodaleinstitute.org/why-organic/issues-and-prioritie...
Your other argument isn't especially persuasive, either. Statistically, is vitamin deficiency a serious public health problem in America? Whatever "protein, calcium, phosphorus, iron, riboflavin, and vitamin C" reduction there has been in corn over the last 50 years, it's extremely unlikely to have offset a factor of 8 increase in productivity.
Actually it does. 90 million acres of corn were planted for livestock in 2018 [0] and we know that the nutritional density of corn has declined [1]. So the long term is we just keep yielding higher with lower nutritional value? The main reason we're after higher yields is livestock and mass produced "junk" food which provides what positive value? The sustainability problem aside, how does this benefit us globally and long term?
> Statistically, is vitamin deficiency a serious public health problem in America?
Is it a problem? Yes. [2] In America? Past studies [3] have shown this and I don't think it's a stretch to just look at the health epidemic here which is, generally, systemic from poor overall nutrition. [4]
Sure, the productivity factor is in our "favor", at least by the numbers. But it's very clear that there is negative impact that extends beyond just the yielded nutritional value. It flows down into additional consumption and requirements to fortify nutritionally sparse natural ingredients.
[0] https://www.ers.usda.gov/topics/crops/corn-and-other-feedgra... [1] https://journals.ashs.org/hortsci/view/journals/hortsci/44/1... [2] https://academic.oup.com/jxb/article/55/396/353/489122 [3] https://www.cdc.gov/nutritionreport/pdf/4Page_%202nd%20Nutri... [4] https://www.military.com/daily-news/2017/10/15/too-fat-to-fi...