I think you could make the knucks manly.
I did mine in a maggie DK tweed. Of course they aren't technically washable but i would probably forget that when they get dirty and wash them anyway. (but i don't work in fields either so my dirt and the dirt you are probably dealing with will be a little different! ) i think the ones i did would look very manly if i hadn't used the bright embroidery. i loved that they were knitted from the knuckles down too. if they aren't a surprise you could have him try on the fingers as you go to make sure they are the length you want!