The farmer is out there with his tractor, I guess, turning over the topsoil prior to flooding and transplanting of seedlings. A crow is hopping along behind, guzzling the creepy-crawlies upturned? ‘sunday morning’ would seem to have more to do with the poet’s state of mind than the farmer’s activity. ‘monday morning’ would certainly not work as well. The lazy, natural order of things is felt.
A saying 「権兵衛が種まきゃ烏がほじくる」 (Gonbe ga tane makya, karasu ga hojikuru): In a moment Gonbe (a male farmer’s name) seeds, a craw digs up the ground to eat the crops. – literally meaning an infinite, wasteful effort, but it does absoluely not to suggest a serious problem. Rather, it’s such a light, humorous effort as often made by a child.
Your haiku reminded me an actual this saying-related scene. Yes, peaceful!