For example, you obviously don’t plant alfalfa in a field that is waterlogged every spring.
Source:
https://extension.umaine.edu/publications/2272e/
Concern:
There's a river behind it. Where that field ends, pretty much almost exactly, there's an embankment and it drops immediately to a river that floods basically every year, sometimes quite spectacularly.
And, 'cause this is the Internet and text doesn't convey things very well, I'll also add that I'm in no way calling you wrong.
I'm simply giving you more information in hopes that you can solve the mystery, assuming you're actually curious.
I'm merely pointing this out for your consideration. I don't know and this is (strangely enough) not my domain. Until recently, my only crops were trees and blueberries. They kinda take care of themselves! ;-)
Ok, 2nd guess is clover. A common cover crop for fallow fields.
Hmm...
I didn't notice any flowering - but that doesn't mean it didn't happen.
These also appear to have been (unevenly) planted in rows. They're not consistent spacing - but they line up in rows.
I think clover is seeded with the cast method. Could clover being cast result in fairly (not completely, but definitely not natural) spacing like that? I'd guess the rows are 12" apart - maybe 18" apart.
They also aren't in straight rows - like they drove around in the shape of the field and planted 'em with some sort of planter implement?
I don't plant clover, either. We do have hay fields but, again, Mother Nature takes care of all that for us. Looking into cash crops of alfalfa and clover varieties (as well as to cut down on expenses 'cause we buy some for the horses) is actually on my list of shit to do - but I haven't gotten that far and I'll probably have the employees do the vast majority of research and make the final decision.
shrugs
I suppose I'm not very helpful. Sorry 'bout that.
I did think it was potato, at first. Then, I noticed that it's not in mounds.
Not soybeans then.