Excellent poem, Craig. My only suggestion would be to change 'They work so hard well into the dark' to 'They work so hard, well into dark.' It still makes sense but by dropping the 'the' I feel it flows a little more smoothly there. Apart from that, the rhyming is effortless.
When I read this I think of our local sugarcane workers here. Yes, working in the fields is really hard work and they are paid only around $2 a day. They are our unsung heroes as our sugar industry wouldn't survive without them. Great poem.