I had never heard of them either so of course I Googled.
https://extension.entm.purdue.edu/fi...orn-maggot.php
They seem to be mostly a pest of corn and they look too large to be causing trouble with your carrot or spinach seeds. Many people have trouble with getting spinach seeds to germinate. they can be finicky.
Have you opened your pea seeds and found maggots inside? Why do you think that it's corn maggots?
Things may be different in Arkansas but I live in PA and I garden organically so I have way more organic matter than average in my garden. Average is 4% and I usually have about 10% according to my soil test. I have no germination issues.